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This study determined effects of full-fatted (C046, 41% crude protein) and lipid extracted (LEA, 39% crude protein) microalgae Desmodesmus sp. on growth performance, gut health, and excreta hydrothermal liquefaction of broiler chickens. Two experiments were conducted by feeding day-old Cornish male chicks: 1) a corn-soybean meal basal diet (control) 2) control +5% C046, or 3) control +5% LEA for 2 weeks. Growth performance was measured weekly in both experiments. Blood, liver, and duodenum samples of chickens were collected for biochemical analyses, and excreta samples were collected for hydrothermal liquefaction (300 °C, 60 min) at the end of Experiment 2. Compared with the control, supplemental dietary C046 and LEA enhanced average daily gain (13% to 40%, p < 0.05) in both experiments, and improved feed efficiency (15% and 11%, p < 0.01) in Experiment 2. The C046 and LEA diets enhanced the duodenum (19% to –2 fold, p < 0.05), but decreased the liver (17 to 78%, p < 0.05) mRNA abundances of interleukins-1, 6 and 8 and (or) tumor necrosis factor-α, respectively, compared with the controls. Meanwhile, the two types of biomass enhanced the protein amounts of claudin-1 in the duodenum (5–34%, p < 0.05) than the controls. Hydrothermal liquefaction of the excreta derived from the three diets showed no major differences in total bio-crude oil (average of 23%), hydrochar yield (average of 12%), or elemental compositions. However, the heating values of the resultant two bio-crude oils from the microalgae-fed chicken excreta (average of 34 MJ/kg) were 16% greater than those from the control chickens (29 MJ/kg). In conclusion, supplementing the full- and de-fatted Desmodesmus sp. microalgal biomass in the starter diets for broiler chickens produced largely similar improvements of growth performance, gut health, and excreta-derived oil quality.
Sun T, Wang K, Wyman B, Sudibyo H, Liu G, Beal C, Manning S, Johnson ZI, Aydemir TB, Tester JW, Lei XG (2021). Supplemental dietary full-fatted and defatted Desmodesmus sp. exerted similar effects on growth performance, gut health, and excreta hydrothermal liquefaction of broiler chicks. Algal Research 54: 102205. https://doi.org/10.1016/j.algal.2021.102205
The database on ocean primary productivity comprises over two decades (1985–2008) of data that the authors have participated in collecting, using the assimilation of inorganic 14C through photosynthesis, in incubations carried out in situ. The dataset is perhaps unique in that it uses, overwhelmingly, consistent methodology while covering a wide geographic range. Ancillary data are included. Using the database, it is hoped that investigators can test for the relationships among the environmental drivers for ocean productivity, the meaning of the 14C method in terms of phytoplankton physiology and the dynamics in the water column, and as a resource for further development of productivity algorithms using satellite ocean color imagery.
Marra JF, Barber RT, Barber E, Bidigare RR, Chamberlin WS, Goericke R, Hargreaves BR, Hiscock M, Iturriaga R, Johnson ZI, Kiefer DA, Kinkade C, Knudson C, Lance V, Langdon C, Lee Z-P, Perry MJ, Smith WO, Vaillancourt R, Zoffoli L (2020). A database of ocean primary productivity from the 14C method. Limnology and Oceanography Letters. https://doi.org/10.1002/lol2.10175
While disappointingly not algae related….unless it is….Lauren was a winner at the 2020 DUML pumpkin carving competition. Well done!
Xie N, Hunt DE, Johnson ZI, He Y, Wang G (2020). Annual Partitioning Patterns of Labyrinthulomycetes Reveal Their Multifaceted Role in Marine Microbial Food Webs. Appl Environ Microbiol: AEM.01652-01620. https://doi.org/10.1128/aem.01652-20
Heterotrophic microbes play a key role in remineralizing organic material in the coastal ocean. While there is a significant body of literature examining heterotrophic bacterioplankton and phytoplankton communities, much less is known about the diversity, dynamics, and ecology of eukaryotic heterotrophs. Here we focus on the Labyrinthulomycetes, a fungus-like protistan group whose biomass can exceed that of the bacterioplankton in coastal waters. We examined their diversity and community structure in a weekly temperate coastal ocean time series. Their seasonal community patterns were related to temperature, insolation, dissolved inorganic carbon, fungal abundance, ammonia, chlorophyll a, pH, and other environmental variables. Similar to the bacterioplankton, annual community patterns of the Labyrinthulomycetes were dominated by a few persistent taxa with summer or winter preferences. However, like the patterns of fungi at this site, the majority of the Labyrinthulomycetes phylotypes occurred mostly as short, reoccurring, season-specific blooms. Furthermore, some of specific phylotypes of Labyrinthulomycetes displayed time-lagged correlations or co-occurrences with bacterial, algal, or fungal phylotypes, suggesting their potentially multifaceted involvement in the marine food webs. Overall, this study reports niche partitioning between closely-related Labyrinthulomycetes and identifies distinct ecotypes and temporal patterns compared to bacterioplankton and fungi.
Economical production of algal commodities (food, feed, and fuels) requires reusing cultivation water to reduce operating costs. While some algae strains show growth inhibition in reused water, other strains appear unaffected. Reusing water to grow different strains (i.e., crop rotation) could potentially improve overall biomass production compared to water reuse with the same strain by reducing accumulation of strain-specific waste products, limiting carryover of population-specific pathogens such as viruses, and introducing bacteria that degrade residual organic matter. Here, batch culture experiments tested the effects of reused cultivation water from the self-inhibiting diatom Staurosira sp. C323 on the diatom Navicula sp. SFP and green alga Chlorella sp. D046, as well as their microbiomes. Navicula sp. and Chlorella sp. grew well in Staurosira sp. reused water, indicating that previously observed self-inhibition was likely specific to this Staurosira strain. While algal microbiomes were not significantly different between controls and reused water treatments, specific bacteria taxa were differentially abundant in reused treatments, suggesting that some taxa responded to compounds remaining in the reused water. Results suggest that algae growth responses in reused water may depend largely on strain-specific factors, and that crop rotation can support biomass production.
Loftus SE, Hunt DE, Johnson ZI (2020). Reused cultivation water from a self-inhibiting alga does not inhibit other algae but alters their microbiomes. Algal Research 51: 102067. DOI: 10.1016/j.algal.2020.102067
Ambient conditions shape microbiome responses to both short- and long-duration environment changes through processes including physiological acclimation, compositional shifts, and evolution. Thus, we predict that microbial communities inhabiting locations with larger diel, episodic, and annual variability in temperature and pH should be less sensitive to shifts in these climate-change factors. To test this hypothesis, we compared responses of surface ocean microbes from more variable (nearshore) and more constant (offshore) sites to short-term factorial warming (+3 °C) and/or acidification (pH −0.3). In all cases, warming alone significantly altered microbial community composition, while acidification had a minor influence. Compared with nearshore microbes, warmed offshore microbiomes exhibited larger changes in community composition, phylotype abundances, respiration rates, and metatranscriptomes, suggesting increased sensitivity of microbes from the less-variable environment. Moreover, while warming increased respiration rates, offshore metatranscriptomes yielded evidence of thermal stress responses in protein synthesis, heat shock proteins, and regulation. Future oceans with warmer waters may enhance overall metabolic and biogeochemical rates, but they will host altered microbial communities, especially in relatively thermally stable regions of the oceans.
Wang Z, Tsementzi D, Williams TC, Juarez DL, Blinebry SK, Garcia NS, Sienkiewicz BK, Konstantinidis KT, Johnson ZI, Hunt DE (2020). Environmental stability impacts the differential sensitivity of marine microbiomes to increases in temperature and acidity. The ISME Journal. https://doi.org/10.1038/s41396-020-00748-2
A substantial body of research now exists demonstrating sensitivities of marine organisms to ocean acidification (OA) in laboratory settings. However, corresponding in situ observations of marine species or ecosystem changes that can be unequivocally attributed to anthropogenic OA are limited. Challenges remain in detecting and attributing OA effects in nature, in part because multiple environmental changes are co-occurring with OA, all of which have the potential to influence marine ecosystem responses. Furthermore, the change in ocean pH since the industrial revolution is small relative to the natural variability within many systems, making it difficult to detect, and in some cases, has yet to cross physiological thresholds. The small number of studies that clearly document OA impacts in nature cannot be interpreted as a lack of larger-scale attributable impacts at the present time or in the future but highlights the need for innovative research approaches and analyses. We summarize the general findings in four relatively well-studied marine groups (seagrasses, pteropods, oysters, and coral reefs) and integrate overarching themes to highlight the challenges involved in detecting and attributing the effects of OA in natural environments. We then discuss four potential strategies to better evaluate and attribute OA impacts on species and ecosystems. First, we highlight the need for work quantifying the anthropogenic input of CO2 in coastal and open-ocean waters to understand how this increase in CO2 interacts with other physical and chemical factors to drive organismal conditions. Second, understanding OA-induced changes in population-level demography, potentially increased sensitivities in certain life stages, and how these effects scale to ecosystem-level processes (e.g. community metabolism) will improve our ability to attribute impacts to OA among co-varying parameters. Third, there is a great need to understand the potential modulation of OA impacts through the interplay of ecology and evolution (eco–evo dynamics). Lastly, further research efforts designed to detect, quantify, and project the effects of OA on marine organisms and ecosystems utilizing a comparative approach with long-term data sets will also provide critical information for informing the management of marine ecosystems.
Doo SS, Kealoha A, Andersson A, Cohen AL, Hicks TL, Johnson ZI, Long MH, McElhany P, Mollica N, Shamberger KEF, Silbiger NJ, Takeshita Y, Busch DS (2020). The challenges of detecting and attributing ocean acidification impacts on marine ecosystems. ICES Journal of Marine Science. https://doi.org/10.1093/icesjms/fsaa094
Coastal acidification in southeastern U.S. estuaries and coastal waters is influenced by biological activity, run-off from the land, and increasing carbon dioxide in the atmosphere. Acidification can negatively impact coastal resources such as shellfish, finfish, and coral reefs, and the communities that rely on them. Organismal responses for species located in the U.S. Southeast document large negative impacts of acidification, especially in larval stages. For example, the toxicity of pesticides increases under acidified conditions and the combination of acidification and low oxygen has profoundly negative influences on genes regulating oxygen consumption. In corals, the rate of calcification decreases with acidification and processes such as wound recovery, reproduction, and recruitment are negatively impacted. Minimizing the changes in global ocean chemistry will ultimately depend on the reduction of carbon dioxide emissions, but adaptation to these changes and mitigation of the local stressors that exacerbate global acidification can be addressed locally. The evolution of our knowledge of acidification, from basic understanding of the problem to the emergence of applied research and monitoring, has been facilitated by the development of regional Coastal Acidification Networks (CANs) across the United States. This synthesis is a product of the Southeast Coastal and Ocean Acidification Network (SOCAN). SOCAN was established to better understand acidification in the coastal waters of the U.S. Southeast and to foster communication among scientists, resource managers, businesses, and governments in the region. Here we review acidification issues in the U.S. Southeast, including the regional mechanisms of acidification and their potential impacts on biological resources and coastal communities. We recommend research and monitoring priorities and discuss the role SOCAN has in advancing acidification research and mitigation of and adaptation to these changes.
Hall ER, Wickes L, Burnett LE, Scott GI, Hernandez D, Yates KK, Barbero L, Reimer JJ, Baalousha M, Mintz J, Cai W-J, Craig JK, DeVoe MR, Fisher WS, Hathaway TK, Jewett EB, Johnson Z, Keener P, Mordecai RS, Noakes S, Phillips C, Sandifer PA, Schnetzer A, Styron J (2020). Acidification in the U.S. Southeast: Causes, Potential Consequences and the Role of the Southeast Ocean and Coastal Acidification Network. Frontiers in Marine Science 7. https://doi.org/10.3389/fmars.2020.00548
The Pivers Island Coastal Observatory turned 10-years old today! What started out as an undergraduate summer project focused on nearshore ocean acidification, has blossomed into a comprehensive microbial and biogeochemical time-series with more than 1000 time points (and still going) and with extensions to the open ocean. We look forward to another decade of contributions to microbial oceanography using PICO as a sentinel of local and global change.
Microalgae hold great promise as environmentally sustainable sources of food, animal feed, and fuel. However, large amounts of water are used during microalgae cultivation and this negatively impacts economic viability and environmental sustainability. Reusing cultivation water can reduce the direct impacts of water usage and also reduce nutrient requirements and algal wastewater treatment. However, studies have shown that algae growth in reused water can be compromised, unaffected, or sometimes enhanced compared to controls. This review examines recent studies on water reuse to qualitatively understand these varied effects. Growth inhibitors and stimulators in reused water and their underlying mechanisms are discussed, as well as recent pre-treatment technologies and factors affecting the quality of reused water, such as microalgae taxa, culture conditions, and harvesting methods, are considered. A scheme is proposed for water reuse and harvesting methods based on the desired algal end products. Taking these findings together, here we provide recommendations for further research directions as well as new insights into designing and integrating a cultivation strategy with a harvesting platform to reuse water for more efficient microalgae cultivation.
Lu Z, Loftus S, Sha J, Wang W, Park MS, Zhang X, Johnson ZI, Hu Q (2020). Water reuse for sustainable microalgae cultivation: Current knowledge and future directions. Resources, Conservation and Recycling 161: 104975. https://doi.org/10.1016/j.resconrec.2020.104975
The Pivers Island Coastal Observatory (PICO) sampled its 1000th time point today. The time-series, was started in 2010 by a Duke undergraduate (Christina C.) interested in the temporal variability of ocean acidification. Ten years later, the time-series has generated a rich, publically available dataset to examine the physical, chemical and biological variability associated with regular processes (e.g. seasons and tides) and episodic events (e.g. hurricanes). Over 50 trainees, undergraduates, graduate students, PIs and other scientists have been part of the sampling. Fittingly, today’s sampling was carried out by Sara Blinebry who has sampled PICO the most over the course of the ten years. Congratulations to all and looking forward to another 1000 time-points!
Keep up! 🙂
The Duke Marine Lab’s Biological Oceanography 2020 class was held aboard the new Duke University research vessel R/V Shearwater. The 77′ power catamaran is a all purpose research vessel with a cruising speed of >20 knots and better than 1000 miles radius. The research vessel had three crew along with the ten members for the inaugural at-sea class. The adventure started in Miami, FL and cruised around Florida visiting Key West, Dry Tortugas and Fort Myers among other locations before returning to Miami via the gulf stream. With a fully functional CTD equipped rosette, along with on-board sampling capabilities, the class carried out numerous onsite depth profiles and underway samplings to characterize biological variability (and its chemical and physical drivers) in this region of the Atlantic Ocean. A trove of data was brought home where everyone had a chance to analyze and interpret as part of broader oceanographic processes. In spite of (or perhaps because of) the close-quarters, everyone had an amazing time and earned their ranks as the pioneering research and educational expedition aboard this amazing vessel. We greatly look forward to more adventures in the future.
Led by Sara, Courtney and Jess, the marine microbe group tree was the ‘crowd favorite’ at this year’s Gingerbread Festival Crab Pot Christmas Tree decorating contest. The tree, themed Sparkling Science in the Deep Blue Sea, was loaded with ornaments that highlight the various types of marine science research and education that occur at the Duke Marine Lab. Perhaps the highlight of the decorations was the moving bubble/water stream that encircled the tree. Further adding to the excitement was the the tree was transported to the venue via boat. Congratulations to Team Microbe!
The decarbonization of agriculture faces many challenges and has received a level of attention insufficient to abate the worst effects of climate change and ensure a sustainable bioeconomy. Agricultural emissions are caused both by fossil-intensive fertilizer use and land-use change, which in turn are driven in part by increasing demand for dietary protein. To address this challenge, we present a synergistic system in which organic waste-derived biogas (a mixture of methane and carbon dioxide) is converted to dietary protein and ammonia fertilizer. This system produces low-carbon fertilizer inputs alongside high-quality protein, addressing the primary drivers of agricultural emissions. If the proposed system were implemented across the United States utilizing readily available organic waste from municipal wastewater, landfills, animal manure, and commercial operations, we estimate 30% of dietary protein intake and 127% of ammonia usage could be displaced while reducing land use, water consumption, and greenhouse gas emissions.
Sagues WJ, Assis CA, Hah P, Sanchez DL, Johnson Z, Acharya M, Jameel H, Park S (2019). Decarbonizing Agriculture through the Conversion of Animal Manure to Dietary Protein and Ammonia Fertilizer. Bioresource Technology: 122493. DOI/10.1016/j.biortech.2019.122493
The marine microbe group held a going away part for Ningdong (Daniel) Xie, a visiting Chinese scholar from Tianjin University, China. While here, Daniel studied marine protists, focusing on Labyrinthulomycetes and Fungi, in our coastal waters. Using the PICO time-series and PICO-LOVE transect he found surprising patterns in the abundance and diversity of these important organisms. Some of the papers he published are here (with more to come!) We’ll miss you!
Xie N, Sen B, Song Z , Zhao Y , Chen Z , Shi W , Zhang Y , Zhang J , Johnson ZI and Wang G (2018), High phylogenetic diversity and abundance pattern of Labyrinthulomycete protists in the coastal waters of the Bohai Sea. Environmental Microbiology. DOI:10.1111/1462-2920.14341
Duan Y, Xie N, Song Z, Ward CS, Yung C-M, Hunt DE, Johnson ZI, Wang G (2018). High-resolution Time-series Reveals Seasonal Patterns of Planktonic Fungi at a Temperate Coastal Ocean Site (Beaufort, North Carolina, USA). Applied & Environmental Microbiology. DOI:10.1128/aem.00967-18
He Y, Sen B, Shang J, He Y, Xie N, Zhang Y, Johnson ZI and Wang G. (2017) Seasonal influence of scallop culture on nutrient flux, bacterial pathogens and bacterioplankton diversity across estuaries off the Bohai Sea Coast of Northern China. Marine Pollution Bulletin. DOI: 10.1016/j.marpolbul.2017.07.062
Liu Y, Singh P, Liang Y, Li J, Xie N, Song Z, Daroch M, Leng K, Johnson ZI, Wang G (2017). Abundance and Molecular Diversity of Thraustochytrids in Coastal Waters of Southern China FEMS Microbiol Ecology. DOI: 10.1093/femsec/fix070
The Johnson Lab hosted several presentations and demonstrations as part of DUML Open House 2019. The exhibits focused on the diversity and role of algae / phytoplankton in the coastal ocean as well as the biotechnological applications of algae for sustainable food, feed and fuels. Hundreds of visitors were able to see first hand how algae is grown and to view both cultured and natural plankton samples. Lots of fun!
Read more about the DUML 2019 Open House here in an article by recent Johnson Lab PhD Sarah Loftus.
Recent studies have focused on linking marine microbial communities with environmental factors, yet relatively little is known about the drivers of microbial community patterns across the complex gradients from the nearshore to open ocean. Here, we examine microbial dynamics in 15 five‐station transects beginning at the estuarine Piver’s Island Coastal Observatory (PICO) time‐series site and continuing 87 km across the continental shelf to the oligotrophic waters of the Sargasso Sea. 16S rRNA gene libraries reveal strong clustering by sampling site with distinct nearshore, continental shelf, and offshore oceanic communities. Water temperature and distance from shore (which serves as a proxy for gradients in factors such as productivity, terrestrial input, and nutrients) both most influence community composition. However, at the phylotype level, modeling shows the distribution of some taxa is linked to temperature, others to distance from shore and some by both factors, highlighting that taxa with distinct environmental preferences underlie apparent clustering by station. Thus, continental margins contain microbial communities that are distinct from those of either the nearshore or offshore environments and contain mixtures of phylotypes with nearshore or offshore preferences rather than those unique to the shelf environment.
Wang Z, Juarez DL, Pan J-F, Blinebry SK, Gronniger J, Clark JS, Johnson ZI, Hunt DE Microbial communities across nearshore to offshore coastal transects are primarily shaped by distance and temperature. Environ Microbiol. DOI: 10.1111/1462-2920.14734
The Pivers Island Coastal Observatory (PICO) weekly (and sometimes more) time-series turned nine today. Started in 2010 as an undergraduate independent student project focusing on ocean acidification, the coastal time-series has matured into a long term coastal sentinel, observing seasonal, yearly and interannual changes in the physics, chemistry and biology of the coastal marine environment with weekly sampling. Additional offshore longitudinal sampling (PICO-LOVE) provides spatial context. Data is available through BCO-DMO. Happy Birthday and hooray for PICO!
Drs. Lu and Johnson both presented at IABBB 2019 meeting in Boulder CO.
Implementation of UV-based advanced oxidation processes in algal medium reuse
Z. Lu, W. Wang, J. Sha, X. Zhang, P. Sun, Q. Hu
Algae show great potential as sustainable feedstock for numerous bioproducts. However, large volume of water consumption during algal biomass production make the culture media recycling is a necessity due to economic and environmental concern. To avoid the negative effect of enriched organic matters in the harvested culture media, pre-treatment prior to medium replenishment and reuse is required. In this study, degradation of algenitic organic matters (AOM) in the culture media by UV-based photolysis processes (i.e., direct UV, UV/peroxydisulfate (PDS), UV/H2O2 and UV/NH2Cl) was explored. The results showed that UV, UV/ PDS, UV/H2O2 and UV/NH2Cl caused a decrease of SUVA for 29.9%, 35.4%, 40.45% and 22.6%, respectively, though the organic matter was almost not mineralized. Fluorescence excitation-emission matrix combined with parallel factor analysis indicated that UV/ PDS and UV/H2O2 degraded 47.26%-56.31% of the fluvic-like and humic-like fractions in AOM. Powder activated carbon absorption and growth evaluation for the AOPs-treated media indicated that UV/ PDS and UV/H2O2 processes not only could remove the growth inhibitors in the media, but also were beneficial to the algae growth. These results suggested that UV/PDS and UV/H2O2 could effectively degradation the hydrophobic components in AOM and converted the growth inhibition fraction of AOM in the recycled media into nutrient source for algal growth. Unlike the general application of UV-based AOP in the wastewater treatment, this study provided an innovative idea about how to pre-treat AOM in the media recycling: utilization rather than removal, which was a more sustainable and environment-friendly technology.
Algae production from the Marine Algae Industrialization Consortium (MAGIC)
Duke University, USA
Introduction: The Marine Algae Industrialization Consortium (MAGIC) is a group of academic and private institutions that together seek to advance the large scale use of marine algae for the sustainable production of food, feed and fuel. Our team is an integrated pipeline from algae strain selection to production, separation, product assessment and economic and life cycle analyses. Here we present results and interpretation from the outdoor cultivation and harvesting of several top candidate strains. Methods: Numerous taxonomically diverse strains of marine microalgae were grown in outdoor raceway ponds across an annual cycle to investigate factors that lead to enhanced production and recovery of algae biomass for downstream applications. These marine microalgae were grown in a hybrid PBR – raceway pond system that experienced natural environmental variability and thus the range of values recovered represent a real world assessment of production. Results: We show that there is a dramatic variability in the productivity across taxa, environmental conditions, and pond operational parameters with some combinations leading to substantial improvements over ‘standard’ conditions in overall biomass yields. Discussion: These results demonstrate the variability across strains/conditions and the importance of using industrially relevant conditions when design testing infrastructure and operational conditions. The best combinations suggest areas that may be further optimized for future increases in algae productivity. Finally, the biomass generated has excellent biochemical characteristics that support an improved economic assessment of the use of marine algae for the sustainable production of fuel, feed and food.
Reusing growth medium (water supplemented with nutrients) for microalgae cultivation is required for economical and environmentally sustainable production of algae bioproducts (fuels, feed, and food). However, reused medium often contains microbes and dissolved organic matter that may affect algae growth. While the accumulation of dissolved organic carbon (DOC) in reused medium has been demonstrated, it is unclear whether DOC concentrations affect algae growth or subsequent rates of algal DOC release. To address these questions, lab-scale experiments were conducted with three marine microalgae strains, Navicula sp. SFP, Staurosira sp. C323, and Chlorella sp. D046, grown in medium reused up to four times. Navicula sp. and Chlorella sp. grew similarly in reused medium as in fresh medium, while Staurosira sp. became completely inhibited in reused medium. Across the three algae, there was no broad trend between initial DOC concentration in reused medium and algae growth response. Navicula sp. released less DOC overall in reused medium than in fresh medium, but DOC release rates did not decrease proportionally with increased DOC concentrations. Net DOC accumulation was much lower than gross DOC released by Navicula sp. and Staurosira sp., indicating the majority of released DOC was degraded. Additionally, biodegradation experiments with reused media showed no further net decrease in DOC, suggesting the accumulated DOC was recalcitrant to the associated bacteria. Overall, these results suggest that taxa-specific factors may be responsible for algae growth response in reused medium, and that DOC release and accumulation are insensitive to prior cultivation rounds. Choosing an algae strain that is uninhibited by accumulated DOC is therefore critical to ensure successful water reuse in the algae industry.
Loftus SE, Johnson ZI (2019). Reused Cultivation Water Accumulates Dissolved Organic Carbon and Uniquely Influences Different Marine Microalgae. Frontiers in Bioengineering and Biotechnology 7. http://doi.org/10.3389/fbioe.2019.00101
PhD student Sarah Loftus attended the 2019 ASLO Aquatic Sciences Meeting in San Juan, Puerto Rico. ASLO’s mission is to “foster a diverse, international scientific community that creates, integrates and communicates knowledge across the full spectrum of aquatic sciences, advances public awareness and education about aquatic resources and research, and promotes scientific stewardship of aquatic resources for the public interest.” Loftus presented her PhD research in the special session on Phytoplankton-Bacteria Interactions, with a talk titled “Effects of DOC pools on phytoplankton growth and bacteria communities.” She was also selected to participate in ASLO’s Journalist for a Day program, which involves writing an article about research presented at the conference. Articles from this program will be published in the August issue of the Limnology & Oceanography Bulletin.
Subsurface chlorophyll maximum layers (SCMLs) are nearly ubiquitous in stratified water columns and exist at horizontal scales ranging from the submesoscale to the extent of oligotrophic gyres. These layers of heightened chlorophyll and/or phytoplankton concentrations are generally thought to be a consequence of a balance between light energy from above and a limiting nutrient flux from below, typically nitrate (NO3). Here we present multiple lines of evidence demonstrating that iron (Fe) limits or with light colimits phytoplankton communities in SCMLs along a primary productivity gradient from coastal to oligotrophic offshore waters in the southern California Current ecosystem. SCML phytoplankton responded markedly to added Fe or Fe/light in experimental incubations and transcripts of diatom and picoeukaryote Fe stress genes were strikingly abundant in SCML metatranscriptomes. Using a biogeochemical proxy with data from a 40-y time series, we find that diatoms growing in California Current SCMLs are persistently Fe deficient during the spring and summer growing season. We also find that the spatial extent of Fe deficiency within California Current SCMLs has significantly increased over the last 25 y in line with a regional climate index. Finally, we show that diatom Fe deficiency may be common in the subsurface of major upwelling zones worldwide. Our results have important implications for our understanding of the biogeochemical consequences of marine SCML formation and maintenance.
Hogle SL, Dupont CL, Hopkinson BM, King AL, Buck KN, Roe KL, Stuart RK, Allen AE, Mann EL, Johnson ZI, Barbeau KA (2018). Pervasive iron limitation at subsurface chlorophyll maxima of the California Current. Proc Natl Acad Sci U S A: 201813192. DOI: 10.1073/pnas.1813192115
Salmonid feeds can be formulated with high quality microalgae to maintain sustainability in the aquaculture industry. But, the suitability of different microalgae species as potential feed ingredients needs to be documented to enable ready acceptance by the farming industry. The aim of the present study is to investigate the potential of the microalga Scenedesmus sp. as a major ingredient in low fishmeal feeds of Atlantic salmon. Three feeds were formulated with Scenedesmus/fishmeal, at inclusion levels of 0/10, 10/5 and 20/2.5% (CT, SCE 10 and SCE 20, respectively); to investigate the effect of the ingredient on the weight gain, growth rate, feed conversion ratio, nutrient retention and chemical composition and nutrient digestibility in Atlantic salmon. In addition, the physical characteristics of feeds were investigated to assess the impact of the alga-incorporation on the quality of the feeds. Fish (initial average weight of 229 g) in 6 replicate tanks were fed one of the experimental feeds for 65 days. The results showed that fish fed SCE 20 had significantly lower weight gain, specific growth rate, thermal growth coefficient and feed conversion ratio than the CT group, which did not receive the microalga. Furthermore, the condition factor and protein efficiency ratio of the microalga-fed groups were lower than the CT group. Hepatosomatic and viscerosomatic indices of the groups did not differ significantly. Ash and protein content of whole fish fed SCE 20 were significantly higher, but dry matter, lipid, and energy of this group were lower than either the CT or the SCE 10 group. Retention of lipid and energy of all groups differed significantly, while that of protein was significantly different in the Scenedesmus-fed groups. Compared to the CT feed, digestibility of dry matter, protein, and energy in the algal feeds were significantly reduced. The highest fat leakage observed for the feed devoid of the alga and the hardness of the SCE 20 feed points to the better physical stability of the alga-containing feeds. Higher contents of n-3 fatty acids and PUFAs were found in the whole body of fish fed SCE 10. In conclusion, Scenedesmus sp. can be incorporated in low fishmeal diets for Atlantic salmon, at inclusion levels below 10%.
Gong Y, Bandara T, Huntley M, Johnson ZI, Dias J, Dahle D, Sørensen M, Kiron V (2018). Microalgae Scenedesmus sp. as a potential ingredient in low fishmeal diets for Atlantic salmon (Salmo salar L.). Aquaculture. DOI: 10.1016/j.aquaculture.2018.11.049
The Second State of the Carbon Cycle Report (SOCCR2) was released by the U.S. Global Change Research Program (USGCRP) via https://carbon2018.globalchange.gov on Friday, November 23, 2018. With over 200 contributing experts including PI Johnson, this interagency Highly Influential Scientific Assessment was led by the Carbon Cycle Interagency Working Group (CCIWG) and U.S. Carbon Cycle Science Program under USGCRP auspices. SOCCR2 is an authoritative decadal assessment of carbon cycle science across North America, developed by over 200 experts from the U.S., Canadian and Mexican governments, national laboratories, universities, private sector, and research institutions. SOCCR2 is a Sustained Assessment Product of the U.S. Global Change Research Program.
USGCRP, 2018: Second State of the Carbon Cycle Report (SOCCR2): A Sustained Assessment Report. [Cavallaro, N., G. Shrestha, R. Birdsey, M. A. Mayes, R. G. Najjar, S. C. Reed, P. Romero-Lankao, and Z. Zhu (eds.)]. U.S. Global Change Research Program, Washington, DC, USA, 878 pp., https://doi.org/10.7930/SOCCR2.2018.
Peggy Mullin, visiting UNC student who is working with the Johnson Lab on modeling outdoor large scale algae growth, successfully defended her undergraduate honor’s thesis. The thesis, “Development of a laboratory metric to predict large scale algae productivity” uses small scale, rapid laboratory measurements in conjunction with environmental data and mathematical modeling to predict outdoor algae production. This work is an important step towards the broader implementation of the use of marine algae for the sustainable production of food, feed and fuel. Congratulations Peggy!
PhD graduate student Sarah Loftus was the top prize winner of the biology section at the Algae Biomass Summit. The Summit is the algae industry’s premier event, where leading producers of algae products go to network with industry suppliers and technology providers, where project developers converse with utility executives, and where researchers and technology developers rub elbows with venture capitalists. Ms. Loftus presented on recycled water use for industrial applications of algae. Congratulations!
Recycled algae cultivation water steadily accumulates dissolved organic carbon
Summary: Reusing cultivation water is required for economical and environmentally sustainable production of algal biofuels and co-products. However, recycled water contains compounds released by algae that can affect their growth. Previous studies have measured dissolved organic carbon (DOC) accumulation in recycled water, yet none have determined if recycled water affects DOC release or if DOC concentrations predict growth success in recycled water. Here, lab-scale water recycling experiments showed that different algae responded uniquely to recycled growth medium, but growth responses did not correlate with DOC concentration. DOC release rates were lower on average in recycled medium, although there was no trend of decreasing release rates across multiple water reuses. Accumulated DOC in recycled water was also not degraded, so at least a portion may be recalcitrant (i.e., non-biodegradable). Results can inform algae selection and cultivation decisions to maximize both the quality of recycled water and the carbon retained in algae biomass.
There is a growing awareness of the ecological and biogeochemical importance of fungi in coastal marine systems, while highly diverse fungi have been discovered in these marine systems, still little is known about their seasonality and associated drivers in coastal waters. Here, we examined fungal communities over three years of weekly samples at a dynamic, temperate coastal site (Piver’s Island Coastal Observatory (PICO), Beaufort NC USA). Fungal 18S rRNA gene abundance, OTU richness and Shannon’s diversity exhibited prominent seasonality. Fungi 18S rRNA gene copies peak in abundance during the summer and fall, with positive correlations with chlorophyll a, SiO4 and oxygen saturation. Diversity (measured using Internal Transcribed Spacer: ITS libraries) was highest during winter and lowest during summer; it was linked to temperature, pH, chlorophyll a, insolation, salinity, and DIC. Fungal community ITS libraries were dominated throughout the year by Ascomycota with contributions from Basidiomycota, Chytridiomycota and Mucoromycotina, with seasonal patterns linked to water temperature, light, and the carbonate system. Network analysis revealed that while co-occurrence and exclusion existed within fungal network, exclusion dominated the fungi and phytoplankton network, in contrast with reported pathogenic and nutritional interactions between marine phytoplankton and fungi. Compared with the seasonality of bacterial community in the same samples, the timing, extent and associated environmental variables for fungi community are unique. These results highlighted the fungal seasonal dynamics in coastal water and improve our understanding of the ecology of planktonic fungi.ImportanceCoastal fungal dynamics were long assumed to be due to terrestrial inputs; here, a high-resolution time-series, reveals strong, repeating annual patterns linked to in situ environmental conditions, arguing for a resident coastal fungal community shaped by environmental factors. These seasonal patterns do, however, differ from those observed in the bacterioplankton at the same site: e.g., fungal diversity peaks in winter whereas bacterial diversity maxima occur in the spring and fall. While dynamics of these communities are linked to water temperature and insolation, fungi are also influenced by the carbonate system (pH and DIC). As both fungi and heterotrophic bacteria are thought to be key organic material metabolizers, differences in their environmental drivers may offer clues as to which group dominates secondary production at this dynamic site. Overall, this study suggests the unique ecological roles of mycoplankton and their potentially broad niche complementarities to other microbial groups in the coastal ocean.
Duan Y, Xie N, Song Z, Ward CS, Yung C-M, Hunt DE, Johnson ZI, Wang G (2018). High-resolution Time-series Reveals Seasonal Patterns of Planktonic Fungi at a Temperate Coastal Ocean Site (Beaufort, North Carolina, USA). Appl Environ Microbiol. http://doi.org/10.1128/aem.00967-18
The unicellular Labyrinthulomycete protists have long been considered to play a significant role in ocean carbon cycling. However, their distribution and biogeochemical function remain poorly understood. We present a large‐scale study of their spatiotemporal abundance and diversity in the coastal waters of Bohai Sea using flow cytometry and high‐throughput sequencing. These protists display niche preferences and episodic higher biomass than that of bacterioplankton with much phylogenetic diversity (> 4000 OTUs) ever reported. They were ubiquitous with a typical abundance range of 100–1000 cells ml−1 and biomass range of 0.06–574.59 μg C L−1. The observed spatiotemporal abundance variations support the current ‘left‐over scavengers’ nutritional model and highlight these protists as a significant component of the marine microbial loop. The higher average abundance and phylogenetic diversity in the nearshore compared with those in the offshore reveal their predominant role in the terrigenous matter decomposition. Furthermore, the differential relationship of the protist genera to environmental conditions together with their co‐occurrence network suggests their unique substrate preferences and niche partitioning. With few subnetworks and possible keystone species, their network topology indicates community resilience and high connectance level of few operational taxonomic units (OTUs). We demonstrate the significant contribution of these protists to the secondary production and nutrient cycling in the coastal waters. As secondary producers, their role will become more important with increasingly coastal eutrophication.
Xie N, Sen B, Song Z , Zhao Y , Chen Z , Shi W , Zhang Y , Zhang J , Johnson ZI and Wang G (2018), High phylogenetic diversity and abundance pattern of Labyrinthulomycete protists in the coastal waters of the Bohai Sea. Environmental Microbiology . DOI:10.1111/1462-2920.14341
The annual Duke Marine Lab Open House had exceptional attendance this year as it coincided with alumni weekend and a visit from Duke University President Vincent Price. Johnson Lab members hosted two stations at Open House on the sunny July afternoon. One station showcased the open raceway ponds, a feature of the DOE-funded large-scale algae cultivation project. Visitors were even invited to enter a rubber duck race, cheering for their small plastic toy as it rounded the bend of the raceway pond. Another station taught visitors about the diversity and lifestyles of the algae we research in lab. President Price even peered into a microscope to watch Tetraselmis cells whip around using their tail-like flagella. More photos from the weekend can be viewed on Duke’s Nicholas School news page.
First year PhD student Laura Givens receive an IBIEM Graduate Trainee award. IBIEM (Integrative Bioinformatics for Investigating and Engineering Microbiomes) is an interdisciplinary graduate training program between Duke University and North Carolina A&T State University which brings together scientists from various fields with an interest in microbiome research. IBIEM trainees participate in the Boot Camp, Collaborative Science Practica, and an Interactive seminar Course and other informal interactions to be exposed to multiple levels of interdisciplinary experiences to enable them to address issues of quantitative biology in the context of varying industrial sectors. Congratulations Laura!
The Pivers Island Coastal Observatory (PICO) weekly (and sometimes more) time-series turned eight today. Started in 2010 as an undergraduate independent student project focusing on ocean acidification, the coastal time-series has matured into a long term coastal sentinel, observing seasonal, yearly and interannual changes in the physics, chemistry and biology of the coastal marine environment with weekly sampling. Additional offshore longitudinal sampling (PICO-LOVE) provides spatial context. Data is available through BCO-DMO. Happy Birthday and hooray for PICO!
Volunteers from over a dozen regional institutions welcomed over 160 middle school girls to the event this Saturday. GEST’s mission is to provide hands-on STEM opportunities and female STEM role models to girls in eastern NC. PhD students Courtney Swink and Sarah Loftus were on the GEST planning team, which organized this collaborative outreach event in which girls rotated through different STEM activities and a panel discussion. Courtney Swink led one of the twelve STEM activities. She explained the concept of algae cultivation for biofuels and other products, had girls set up their own algae cultures, and described the outdoor cultivation ponds with a tour.
Ph.D. student Courtney traveled to Washington, D.C. to volunteer at the USA Science & Engineering Festival on Saturday, April 6th. This free 2 day event was held at the Walter E. Washington Convention Center and had over 3,000 exhibitors and 350,000 visitors! The mission of this festival is to stimulate interest in the nation’s youth in science, technology, engineering and math (STEM) related fields.
As a student member of ASLO (Association for the Sciences of Limnology and Oceanography), Courtney participated as a volunteer for the CASS (Consortium of Aquatic Science Societies) booth which shared activities and information about aquatic sciences for all age levels. Students were taught about the different morphologic adaptations of all types of plankton and asked to build their own plankton models to “race” to see who’s creation would sink the slowest. Students also learned about turbidity and how to use a secchi disk. The CASS booth alone interacted with ~3,300 young students, parents and teachers! Many students left the booth with a better understanding of what plankton look like and why they are important in the environment.
Second year PhD student Courtney Swink was awarded a NSF Graduate Research Fellowship Program Fellowship. Her selection as an NSF Graduate Fellowship awardee is a significant accomplishment and was based on her demonstrated potential to contribute to strengthening the vitality of the U.S. science and engineering enterprise. Courtney is researching microbial communities associated with large, industrial scale marine microalgae ponds.
Bioenergy Carbon Capture and Storage (BECCS) has been proposed to reduce atmospheric CO2 concentrations, but concerns remain about competition for arable land and freshwater. The synergistic integration of algae production, which does not require arable land or freshwater, with BECCS (called “ABECCS”) can reduce CO2 emissions without competing with agriculture. This study presents a techno-economic and life-cycle assessment for co-locating a 121-ha algae facility with a 2,680-ha eucalyptus forest for BECCS. The eucalyptus biomass fuels combined heat and power generation (CHP) with subsequent amine based carbon capture and storage (CCS). A portion of the captured CO2 is used for growing algae and the remainder is sequestered. Biomass combustion supplies CO2, heat, and electricity, thus increasing the range of sites suitable for algae cultivation. Economic, energetic, and environmental impacts are considered. The system yields as much protein as soybeans while generating 61.5 TJ of electricity and sequestering 29,600 t of CO2 per year. More energy is generated than consumed and the freshwater footprint is roughly equal to that for soybeans. Financial break-even is achieved for product value combinations ranging from 1) algal biomass sold for $1,780/t without a carbon credit to 2) algal biomass sold for $100/t with a carbon credit of $396/t. Sensitivity analysis shows significant reductions to the cost of carbon sequestration are possible. The ABECCS system represents a unique technology for negative emissions without reducing protein production or increasing water demand, and should therefore be included in the suite of technologies being considered to address global sustainability.
Happy holidays from the Johnson Lab! Hope plankton brings you something good this year. (Plankton converts to coal in ~300 million years.)
Microbial science at Duke is taking a major step forward with the launch of the Duke Microbiome Center (DMC), which is intended to address growing scientific interest in the roles microbial communities play in human health, the environment and biotechnology. The new center expands on the mission of the five-year-old Duke Center for Genomics of Microbial Systems (GeMS) by going beyond genomic analysis of microorganisms. See related article at Duke Today.
Marine aggregates play a critical role in the biological pump, both as a dominant component of carbon flux and as hotspots for organic matter remineralization by microbial communities. In this study, we used laboratory experiments to investigate how aggregate thin layers, such as those commonly found in the coastal ocean, affect the distribution of bacteria and their activity. Diatom aggregates were added to a stratified water column, forming layers within which both microbial concentration and extracellular enzyme activity were substantially increased relative to background levels. Importantly, this enhancement of bacterial concentration and activity persisted long after the marine snow aggregates settled through the tank—that is, 10 times longer than the duration of the aggregate layer at the density interface. Thus, these small-scale microbial interactions within aggregate layers leave behind considerable “carbon processing footprints” in the water column that may affect biogeochemical cycles at much larger temporal and spatial scales.
Prairie JC, Ziervogel K, Camassa R, McLaughlin RM, White BL, Johnson ZI, Arnosti C Ephemeral aggregate layers in the water column leave lasting footprints in the carbon cycle. Limnology and Oceanography Letters. DOI: 10.1002/lol2.10053
Prochlorococcus, the smallest and most abundant phytoplankter in the ocean, is highly sensitive to hydrogen peroxide (HOOH), and co-occurring heterotrophs such as Alteromonas facilitate the growth of Prochlorococcus by scavenging HOOH. Temperature is also a major influence on Prochlorococcus abundance and distribution in the ocean, and studies in other photosynthetic organisms have shown that HOOH and temperature extremes can act together as synergistic stressors. To address potential synergistic effects of temperature and HOOH on Prochlorococcus growth, high- and low-temperature adapted representative strains were cultured at ecologically relevant concentrations under a range of HOOH concentrations and temperatures. Higher concentrations of HOOH severely diminished the permissive temperature range for growth of both Prochlorococcus strains. At the permissive temperatures, the growth rates of both Prochlorococcus strains decreased as a function of HOOH, and cold temperature increased susceptibility of photosystem II to HOOH-mediated damage. Serving as a proxy for the natural community, co-cultured heterotrophic bacteria increased the Prochlorococcus growth rate under these temperatures, and expanded the permissive range of temperature for growth. These studies indicate that in the ocean, the cross-protective function of the microbial community may confer a fitness increase for Prochlorococcus at its temperature extremes, especially near the ocean surface where oxidative stress is highest. This interaction may play a substantial role in defining the realized thermal niche and habitat range of Prochlorococcus with respect to latitude.
Ma L, Calfee BC, Morris JJ, Johnson ZI, Zinser ER (2017). Degradation of hydrogen peroxide at the ocean/’s surface: the influence of the microbial community on the realized thermal niche of Prochlorococcus. ISME J. http://doi.org/10.1038/ismej.2017.182
Associate Professor Zackary Johnson presented on the trends and patterns of coastal and ocean acidification in coastal North Carolina at the Southeastern Ocean and Coastal Acidification Network NC Stakeholder meeting. The presentation was titled, ‘Variability of the carbonate system (including acidity) in a dynamic coastal NC system’. Ocean and coastal acidification are changing the chemistry of seawater with potential effects for economically important marine life and coastal communities. Runoff pollution, land-use change, and a vibrant shellfish industry render North Carolina among the most socioeconomically vulnerable states to future acidification impacts, but an understanding of these changes can provide the tools necessary for coastal industries and ecosystems to mitigate and adapt to these changes.
Dr. Zhiying “Bruce” Lu joined the Johnson Lab as a postdoctoral research associate and funded by the China Research Council. Dr. Lu’s research focuses on using recycled medium (used water) for growing microalgae as a source of food and fuel. At the Johnson Lab he will work as part of the MAGIC team, to cultivate algae at large scale for sustainable food and fuel production.
Five large scale ponds, three ~1000L and two ~4500L , have been installed and are growing microalgae as part of the Marine Algae Industrialization Consortium (MAGIC). The ponds will grow ~10 strains of microalgae to compare their growth characteristics, algae biochemical signatures, and product suitability across a range of potential applications.
The North Pacific Ocean (between approximately 0°N and 50°N) contains the largest continuous ecosystem on Earth. This region plays a vital role in the cycling of globally important nutrients as well as carbon. Although the microbial communities in this region have been assessed, the dynamics of viruses (abundances and production rates) remains understudied. To address this gap, scientific cruises during the winter and summer seasons (2013) covered the North Pacific basin to determine factors that may drive virus abundances and production rates. Along with information on virus particle abundance and production, we collected a spectrum of oceanographic metrics as well as information on microbial diversity. The data suggest that both biotic and abiotic factors affect the distribution of virus particles. Factors influencing virus dynamics did not vary greatly between seasons, although the abundance of viruses was almost an order of magnitude greater in the summer. When considered in the context of microbial community structure, our observations suggest that members of the bacterial phyla Proteobacteria, Planctomycetes, and Bacteroidetes were correlated to both virus abundances and virus production rates: these phyla have been shown to be enriched in particle associated communities. The findings suggest that environmental factors influence virus community functions (e.g., virion particle degradation) and that particle-associated communities may be important drivers of virus activity.
Gainer PJ, Pound HL, Larkin AA, LeCleir GR, DeBruyn JM, Zinser ER, Johnson ZI, Wilhelm SW (2017). Contrasting seasonal drivers of virus abundance and production in the North Pacific Ocean. PLOS ONE 12: e0184371. DOI: 10.1371/journal.pone.0184371
In this study, we investigated the environmental impacts of scallop culture on two coastal estuaries adjacent the Bohai Sea including developing a quantitative PCR assay to assess the abundance of the bacterial pathogens Escherichia coli and Vibrio parahaemolyticus. Scallop culture resulted in a significant reduction of nitrogen, Chlorophyll a, and phosphorous levels in seawater during summer. The abundance of bacteria including V. parahaemolyticus varied significantly across estuaries and breeding seasons and was influenced by nitrate as well as nutrient ratios (Si/DIN, N/P). Bacterioplankton diversity varied across the two estuaries and seasons, and was dominated by Proteobacteria, Cyanobacteria, Actinobacteria, Bacteroidetes. Overall, this study suggests a significant influence of scallop culture on the ecology of adjacent estuaries and offers a sensitive tool for monitoring scallop contamination.
He Y, Sen B, Shang J, He Y, Xie N, Zhang Y, Johnson ZI and Wang G. (2017) Seasonal influence of scallop culture on nutrient flux, bacterial pathogens and bacterioplankton diversity across estuaries off the Bohai Sea Coast of Northern China. Marine Pollution Bulletin. DOI: 10.1016/j.marpolbul.2017.07.062
In spite of challenging weather, the Duke Marine Lab hosted about 500 visitors for it’s 2017 Open House extravaganza. The Marine Microbe Group presented 3 exhibits including examples of ocean acidification, phytoplankton/algae in the coastal ocean and a demonstrating the large scale of production of microalgae for food and fuel. Lots of good questions and participation and looking forward to showing off even more next year.
The Duke Marine Lab joined the Beaufort NC July 4th parade to promote it’s upcoming open house. Lead by REU student Ford Fishman, the R/V Richard Barber was paraded through the streets to cheering residents and visitors alike!
ZIJ presented on the diversity and activity of Prochlorococcus at the OCB2017 summer meeting at WHOI in Woods Hole, MA. The presentation, “Ribosomal RNA and DNA (23S) of Prochlorococcus reveal variable activity and abundance relationships across taxonomic ranks” was based on a study with lead author and former student Alyse Larkin, now at UCI. The work highlights how the fine taxonomic scale of Prochlorococcus has unexpected patterns in activity and suggests population ecological differentiation, regulation and biogeochemistry that are still poorly understood for this keystone microbe.
Abstract: Phytoplankton communities in oligotrophic temperate and tropical oceans are numerically dominated by Prochlorococcus sp., a genetically diverse and biogeochemically important marine cyanobacterium. The phylogenetic clades and subgroups of Prochlorococcus exhibit niche partitioning based on light, temperature and other resources in the ocean, but it is unknown how these clades/ecotypes differ in their in situ activity across large spatiotemporal environmental gradients. Here using relative 23S rRNA:rDNA ratios as a proxy for specific activity, we examine high light (HL) adapted Prochlorococcus across environmental gradients in the surface North Pacific Ocean to (1) determine the coupling between activity and abundance across taxonomic ranks and (2) examine the specific activity among closely related operational taxonomic units (OTUs). We show that activity and abundance are highly correlated for all 97% similarity OTUs of Prochlorococcus across all sites in the surface ocean. However, finer molecular scale resolution (oligotyping) shows significantly more variability in rRNA:rDNA ratios and reveals differing trends among closely related OTUs including different patterns between high and low abundance oligotypes. These results suggest that HL Prochlorococcus populations respond quickly to (a)biotic changes and the mechanisms that lead to uncoupling between activity and abundance (e.g. density dependent processes) are less important for this community at course molecule scales. These findings also suggest that relative Prochlorococcus population abundances at a given location can serve as a proxy for activity, providing an important tool for ecosystem model development. However, uncoupling at fine molecular scales suggests population differentiation and mechanisms of regulation that are still poorly understood, but important for understanding their relative role to biogeochemical cycles.
Alyse Larkin & Zackary Johnson OCB217