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  • 1
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    Microbial communities in the nepheloid layers and hypoxic zones of the Canary Current upwelling system (2018)
    In:  EPIC3MicrobiologyOpen, pp. e705, ISSN: 20458827
    Details
    Publication Date: 2018-10-29
    Description: Eastern boundary upwelling systems (EBUSs) are among the most productive marine environments in the world. The Canary Current upwelling system off the coast of Mauritania and Morocco is the second most productive of the four EBUS, where nutrient-rich waters fuel perennial phytoplankton blooms, evident by high chlorophyll a concentrations off Cape Blanc, Mauritania. High primary production leads to eutrophic waters in the surface layers, whereas sinking phytoplankton debris and horizontally dispersed particles form nepheloid layers (NLs) and hypoxic waters at depth. We used Catalyzed Reporter Deposition Fluorescence In Situ Hybridization (CARD-FISH) in combination with fatty acid (measured as methyl ester; FAME) profiles to investigate the bacterial and archaeal community composition along transects from neritic to pelagic waters within the “giant Cape Blanc filament” in two consecutive years (2010 and 2011), and to evaluate the usage of FAME data for microbial community studies. We also report the first fatty acid profile of Pelagibacterales strain HTCC7211 which was used as a reference profile for the SAR11 clade. Unexpectedly, the reference profile contained low concentrations of long chain fatty acids 18:1 cis11, 18:1 cis11 11methyl, and 19:0 cyclo11–12 fatty acids, the main compounds in other Alphaproteobacteria. Members of the free-living SAR11 clade were found at increased relative abundance in the hypoxic waters in both years. In contrast, the depth profiles of Gammaproteobacteria (including Alteromonas and Pseudoalteromonas), Bacteroidetes, Roseobacter, and Synechococcus showed high abundances of these groups in layers where particle abundance was high, suggesting that particle attachment or association is an important mechanisms of dispersal for these groups. Collectively, our results highlight the influence of NLs, horizontal particle transport, and low oxygen on the structure and dispersal of microbial communities in upwelling systems.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 2
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    Microbial production and consumption of marine dissolved organic matter (2013)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-05-25
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2013
    Description: Marine phytoplankton are the principal producers of oceanic dissolved organic matter (DOM), the organic substrate responsible for secondary production by heterotrophic microbes in the sea. Despite the importance of DOM in marine food webs, details regarding how marine microbes cycle DOM are limited, and few definitive connections have been made between specific producers and consumers. Consumption is thought to depend on the source of the DOM as well as the identity of the consumer; however, it remains unclear how phytoplankton diversity and DOM composition are related, and the metabolic pathways involved in the turnover of DOM by different microbial taxa are largely unknown. The motivation for this thesis is to examine the role of microbial diversity in determining the composition, lability, and physiological consumption of marine DOM. The chemical composition of DOM produced by marine phytoplankton was investigated at the molecular level using mass spectrometry. Results demonstrate that individual phytoplankton strains release a unique suite of organic compounds. Connections between DOM composition and the phylogenetic identity of the producing organism were identified on multiple levels, revealing a direct relationship between phytoplankton diversity and DOM composition. Phytoplankton-derived DOM was also employed in growth assays with oligotrophic bacterioplankton strains to examine effects on heterotrophic growth dynamics. Reproducible responses ranged from suppressed to enhanced growth rates and cell yields, and depended both on the identity of the heterotroph and the source of the DOM. Novel relationships between specific bacterioplankton types and DOM from known biological sources were found, and targets for additional studies on reactive DOM components were identified. The physiology of DOM consumption by a marine Oceanospirillales strain was studied using a combined transcriptomic and untargeted metabolomic approach. The transcriptional response of this bacterium to Prochlorococcus-derived DOM revealed an increase in anabolic processes related to metabolism of carboxylic acids and glucosides, increased gene expression related to proteorhodopsin-based phototrophy, and decreased gene expression related to motility. Putative identification of compounds present in Prochlorococcus-derived DOM supported these responses. Collectively, these findings highlight the potential for linking detailed chemical analyses of labile DOM from a known biological source with bacterioplankton diversity and physiology.
    Description: Financial support for this work was provided by the National Science Foundation Center for Microbial Oceanography: Research and Education (award #EF0424599 and #DBI0424599) including generous contributions from the EDventures program, the Gordon and Betty Moore Foundation (grant #1711), and a student research grant from the Coastal Ocean Institute at the Woods Hole Oceanographic Institution.
    Keywords: Seawater ; Organic compound content ; Marine phytoplankton ; Kilo Moana (Ship) C-MORE BLOOMER Cruise ; Ka`imikai-o-Kanaloa (Ship) Cruise
    Repository Name: Woods Hole Open Access Server
    Type: Thesis
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  • 3
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    Closely related phytoplankton species produce similar suites of dissolved organic matter (2014)
    Frontiers Media
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    Publication Date: 2022-05-26
    Description: © The Author(s), 2014. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Frontiers in Microbiology 5 (2014): 111, doi:10.3389/fmicb.2014.00111.
    Description: Production of dissolved organic matter (DOM) by marine phytoplankton supplies the majority of organic substrate consumed by heterotrophic bacterioplankton in the sea. This production and subsequent consumption converts a vast quantity of carbon, nitrogen, and phosphorus between organic and inorganic forms, directly impacting global cycles of these biologically important elements. Details regarding the chemical composition of DOM produced by marine phytoplankton are sparse, and while often assumed, it is not currently known if phylogenetically distinct groups of marine phytoplankton release characteristic suites of DOM. To investigate the relationship between specific phytoplankton groups and the DOM they release, hydrophobic phytoplankton-derived dissolved organic matter (DOMP) from eight axenic strains was analyzed using high-performance liquid chromatography coupled to mass spectrometry (HPLC-MS). Identification of DOM features derived from Prochlorococcus, Synechococcus, Thalassiosira, and Phaeodactylum revealed DOMP to be complex and highly strain dependent. Connections between DOMP features and the phylogenetic relatedness of these strains were identified on multiple levels of phylogenetic distance, suggesting that marine phytoplankton produce DOM that in part reflects its phylogenetic origin. Chemical information regarding the size and polarity ranges of features from defined biological sources was also obtained. Our findings reveal DOMP composition to be partially conserved among related phytoplankton species, and implicate marine DOM as a potential factor influencing microbial diversity in the sea by acting as a link between autotrophic and heterotrophic microbial community structures.
    Description: This research was supported by grants to Daniel J. Repeta and Sallie W. Chisholm from the Gordon and Betty Moore Foundation and funding to Daniel J. Repeta, Edward F. DeLong, and Sallie W. Chisholm from the National Science Foundation Science and Technology Center Award 0424599.
    Repository Name: Woods Hole Open Access Server
    Type: Article
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    Format: application/vnd.ms-excel
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  • 4
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    Bacterial quorum-sensing signal arrests phytoplankton cell division and impacts virus-induced mortality (2021)
    American Society for Microbiology
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    Publication Date: 2022-05-27
    Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Pollara, S. B., Becker, J. W., Nunn, B. L., Boiteau, R., Repeta, D., Mudge, M. C., Downing, G., Chase, D., Harvey, E. L., & Whalen, K. E. Bacterial quorum-sensing signal arrests phytoplankton cell division and impacts virus-induced mortality. Msphere, 6(3), (2021): e00009-21, https://doi.org/10.1128/mSphere.00009-21.
    Description: Interactions between phytoplankton and heterotrophic bacteria fundamentally shape marine ecosystems by controlling primary production, structuring marine food webs, mediating carbon export, and influencing global climate. Phytoplankton-bacterium interactions are facilitated by secreted compounds; however, linking these chemical signals, their mechanisms of action, and their resultant ecological consequences remains a fundamental challenge. The bacterial quorum-sensing signal 2-heptyl-4-quinolone (HHQ) induces immediate, yet reversible, cellular stasis (no cell division or mortality) in the coccolithophore Emiliania huxleyi; however, the mechanism responsible remains unknown. Using transcriptomic and proteomic approaches in combination with diagnostic biochemical and fluorescent cell-based assays, we show that HHQ exposure leads to prolonged S-phase arrest in phytoplankton coincident with the accumulation of DNA damage and a lack of repair despite the induction of the DNA damage response (DDR). While this effect is reversible, HHQ-exposed phytoplankton were also protected from viral mortality, ascribing a new role of quorum-sensing signals in regulating multitrophic interactions. Furthermore, our data demonstrate that in situ measurements of HHQ coincide with areas of enhanced micro- and nanoplankton biomass. Our results suggest bacterial communication signals as emerging players that may be one of the contributing factors that help structure complex microbial communities throughout the ocean.
    Description: Funding for this work was supported by an NSF grant (OCE-1657808) awarded to K.E.W. and E.L.H. K.E.W. was also supported by a faculty research grant from Haverford College as well as funding from the Koshland Integrated Natural Science Center and Green Fund at Haverford College. E.L.H. was also supported by a Sloan Foundation research fellowship. B.L.N. was supported by an NSF grant (OCE-1633939). M.C.M. was supported by an NIH training grant (T32 HG000035). Mass spectrometry was partially supported by the University of Washington Proteomics Resource (UWPR95794). D.R. was supported by funding through the Gordon and Betty Moore Foundation (grant 6000), a Simons Collaboration for Ocean Processes and Ecology grant (329108), and an NSF grant (OCE-1736280). R.B. was supported by an NSF graduate research fellowship and an NSF grant (OCE-1829761).
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 5
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    Quantitative transcriptomics reveals the growth- and nutrient-dependent response of a streamlined marine methylotroph to methanol and naturally occurring dissolved organic matter (2017)
    American Society for Microbiology
    Details
    Publication Date: 2022-05-26
    Description: © The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in mBio 7 (2016): e01279-16, doi:10.1128/mBio.01279-16.
    Description: The members of the OM43 clade of Betaproteobacteria are abundant coastal methylotrophs with a range of carbon-utilizing capabilities. However, their underlying transcriptional and metabolic responses to shifting conditions or different carbon substrates remain poorly understood. We examined the transcriptional dynamics of OM43 isolate NB0046 subjected to various inorganic nutrient, vitamin, and carbon substrate regimes over different growth phases to (i) develop a quantitative model of its mRNA content; (ii) identify transcriptional markers of physiological activity, nutritional state, and carbon and energy utilization; and (iii) identify pathways involved in methanol or naturally occurring dissolved organic matter (DOM) metabolism. Quantitative transcriptomics, achieved through addition of internal RNA standards, allowed for analyses on a transcripts-per-cell scale. This streamlined bacterium exhibited substantial shifts in total mRNA content (ranging from 1,800 to 17 transcripts cell−1 in the exponential and deep stationary phases, respectively) and gene-specific transcript abundances (〉1,000-fold increases in some cases), depending on the growth phase and nutrient conditions. Carbon metabolism genes exhibited substantial dynamics, including those for ribulose monophosphate, tricarboxylic acid (TCA), and proteorhodopsin, as well as methanol dehydrogenase (xoxF), which, while always the most abundant transcript, increased from 5 to 120 transcripts cell−1 when cultures were nutrient and vitamin amended. In the DOM treatment, upregulation of TCA cycle, methylcitrate cycle, vitamin, and organic phosphorus genes suggested a metabolic route for this complex mixture of carbon substrates. The genome-wide inventory of transcript abundances produced here provides insight into a streamlined marine bacterium’s regulation of carbon metabolism and energy flow, providing benchmarks for evaluating the activity of OM43 populations in situ.
    Description: National Science Foundation (NSF); Simons Foundation; Gordon E. and Betty I. Moore Foundation
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 6
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    Distinct dissolved organic matter sources induce rapid transcriptional responses in coexisting populations of Prochlorococcus, Pelagibacter and the OM60 clade (2014)
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © The Author(s), 2013. This is the author's version of the work. It is posted here by permission of John Wiley & Sons for personal use, not for redistribution. The definitive version was published in Environmental Microbiology 16 (2014): 2815-2830, doi:10.1111/1462-2920.12254.
    Description: A considerable fraction of the Earth's organic carbon exists in dissolved form in seawater. To investigate the roles of planktonic marine microbes in the biogeochemical cycling of this dissolved organic matter (DOM), we performed controlled seawater incubation experiments and followed the responses of an oligotrophic surface water microbial assemblage to perturbations with DOM derived from an axenic culture of Prochlorococcus, or high-molecular weight DOM concentrated from nearby surface waters. The rapid transcriptional responses of both Prochlorococcus and Pelagibacter populations suggested the utilization of organic nitrogen compounds common to both DOM treatments. Along with these responses, both populations demonstrated decreases in gene transcripts associated with nitrogen stress, including those involved in ammonium acquisition. In contrast, responses from low abundance organisms of the NOR5/OM60 gammaproteobacteria were observed later in the experiment, and included elevated levels of gene transcripts associated with polysaccharide uptake and oxidation. In total, these results suggest that numerically dominant oligotrophic microbes rapidly acquire nitrogen from commonly available organic sources, and also point to an important role for carbohydrates found within the DOM pool for sustaining the less abundant microorganisms in these oligotrophic systems.
    Description: This work was supported by a National Science Foundation Science and Technology Center Award EF0424599 (E.F.D and D.M.K.), grants to D.M.K., D.J.R and E.F.D from the Gordon and Betty Moore Foundation, a gift from the Agouron Institute (to E.F.D.) and a fellowship (202180) to A.K.S. from the Canadian Institutes of Health Research (CIHR).
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
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