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  • 1
    Publication Date: 2022-05-25
    Description: Author Posting. © Inter-Research, 2013. This article is posted here by permission of Inter-Research for personal use, not for redistribution. The definitive version was published in Aquatic Microbial Ecology 71 (2013):141-153, doi:10.3354/ame01674.
    Description: Over the last few decades, molecular methods have vastly improved our ability to study the diversity of microbial communities. In molecular diversity surveys, the function of protists is often inferred from phylogeny. Yet these surveys are unable to distinguish between different trophic modes among closely related taxa. Here we present results from a culture-independent study linking bacterivory to the diversity of pelagic protists from 3 depths of a stratified mesotrophic lake. Bacteria were labeled with bromodeoxyuridine (BrdU) and added to lakewater samples; after incubation, total DNA was extracted from filtered samples. Part of the DNA extract was subjected to immunoprecipitation with anti-BrdU antibodies, and then both whole DNA and BrdU-labeled samples were analyzed using 454-pyrosequencing of the v9 region of 18S small subunit rRNA gene amplicons. The results show that a different community of protists exists at each depth, with limited overlap of taxonomic composition between depths. The community of BrdU-labeled protists, deemed putative bacterivores, is largely a subset of the community found in the whole DNA samples. Many of these BrdU-labeled taxa are poorly represented in GenBank and thus are probably rarely isolated and/or uncultured species. Several of the taxa identified as bacterivores are also phototrophs, highlighting the important role of mixotrophy among eukaryotic microbes. Definitive identity of functional traits among taxa requires careful experimentation, yet this method allows a first-pass assay of the trophic role of microbial eukaryotes from environmental samples.
    Description: This work was funded in part by NSF grants OPP-0838847 and OPP-0838955.
    Keywords: Molecular methods ; Microbial community ; Mixotrophy ; Bromodeoxyuridine ; Culture-independent ; Eukaryotic microbes ; Pyrosequencing ; Lake microbes
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 2
    Publication Date: 2022-05-25
    Description: Author Posting. © The Author(s), 2011. 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 FEMS Microbiology Ecology 82 (2012): 242–253, doi:10.1111/j.1574-6941.2011.01253.x.
    Description: Mixotrophy, the combination of phototrophy and heterotrophy within the same individual, is widespread in oceanic systems. Yet, neither the presence nor ecological impact of mixotrophs has been identified in an Arctic marine environment. We quantified nano- and picoplankton during early autumn in the Beaufort Sea and Canada Basin and determined relative rates of bacterivory by heterotrophs and mixotrophs. Results confirmed previous reports of low microbial biomass for Arctic communities in autumn. The impact of bacterivory was relatively low, ranging from 0.6 x 103 to 42.8 x 103 bacteria mL-1 day-1, but it was often dominated by pico- or nano-mixotrophs. From 1-7% of the photosynthetic picoeukaryotes were bacterivorous, while mixotrophic nanoplankton abundance comprised 1-22% of the heterotrophic and 2-32% of the phototrophic nanoplankton abundance, respectively. The estimated daily grazing impact was usually 〈 5% of the bacterial standing stock, but impacts as high as 25% occurred. Analysis of denaturing gradient gel electrophoresis band patterns indicated that communities from different depths at the same site were appreciably different, and that there was a shift in community diversity at the midpoint of the cruise. Sequence information from DGGE bands reflected microbes related to ones from other Arctic studies, particularly from the Beaufort Sea.
    Description: Funding for participation in the 2008 cruise was provided by the Woods Hole Oceanographic Institution Arctic Research Initiative, with additional support from National Science Foundation Grants OPP-0838847 (RWS) and OPP-0838955 (RJG).
    Keywords: Arctic Ocean ; DGGE ; Mixotrophy ; Phytoflagellates ; Picoeukaryotes
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
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  • 3
    Publication Date: 2022-05-25
    Description: © The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Frontiers in Marine Science 5 (2018): 13, doi:10.3389/fmars.2018.00013.
    Description: Identifying putative mixotrophic protist species in the environment is important for understanding their behavior, with the recovery of these species in culture essential for determining the triggers of feeding, grazing rates, and overall impact on bacterial standing stocks. In this project, mixotroph abundances determined using tracer ingestion in water and sea ice samples collected in the Ross Sea, Antarctica during the summer of 2011 were compared with data from the spring (Ross Sea) and fall (Arctic) to examine the impacts of bacterivory/mixotrophy. Mixotrophic nanoplankton (MNAN) were usually less abundant than heterotrophs, but consumed more of the bacterial standing stock per day due to relatively higher ingestion rates (1–7 bacteria mixotroph−1 h−1 vs. 0.1–4 bacteria heterotroph−1 h−1). Yet, even with these high rates observed in the Antarctic summer, mixotrophs appeared to have a smaller contribution to bacterivory than in the Antarctic spring. Additionally, putative mixotroph taxa were identified through incubation experiments accomplished with bromodeoxyuridine-labeled bacteria as food, immunoprecipitation (IP) of labeled DNA, and amplification and high throughput sequencing of the eukaryotic ribosomal V9 region. Putative mixotroph OTUs were identified in the IP samples by taxonomic similarity to known phototroph taxa. OTUs that had increased abundance in IP samples compared to the non-IP samples from both surface and chlorophyll maximum (CM) depths were considered to represent active mixotrophy and include ones taxonomically similar to Dictyocha, Gymnodinium, Pentapharsodinium, and Symbiodinium. These OTUs represent target taxa for isolation and laboratory experiments on triggers for mixotrophy, to be combined with qPCR to estimate their abundance, seasonal distribution and potential impact.
    Description: This work was supported by National Science Foundation Grants OPP-0838955 (RG) and OPP-0838847 (RS).
    Keywords: Protist ; Diversity ; Mixotrophy ; Ross Sea ; Amplicon sequencing
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 4
    Publication Date: 2022-05-25
    Description: Author Posting. © Inter-Research, 2009. This article is posted here by permission of Inter-Research for personal use, not for redistribution. The definitive version was published in Aquatic Microbial Ecology 54 (2009): 269-277, doi:10.3354/ame01276.
    Description: Mixotrophic nanoflagellates (MNF) were quantified in plankton and sea ice of the Ross Sea, Antarctica, during austral spring. Tracer experiments using fluorescently labeled bacteria (FLB) were conducted to enumerate MNF and determine their contribution to total chloroplastidic and total bacterivorous nanoflagellates. Absolute abundances of MNF were typically 〈200 ml–1 in plankton assemblages south of the Polar Front, but they comprised 8 to 42% and 3 to 25% of bacterivorous nanoflagellates in the water column and ice cores, respectively. Moreover, they represented up to 10% of all chloroplastidic nanoflagellates in the water column when the prymnesiophyte Phaeocystis antarctica was blooming (up to 23% if P. antarctica, which did not ingest FLB, was excluded from calculations). In ice cores, MNF comprised 5 to 10% of chloroplastidic nanoflagellates. The highest proportions of MNF were found in some surface water samples and in plankton assemblages beneath ice, suggesting a potentially large effect as bacterial grazers in those locations. This study is the first to report abundances and distributions of mixotrophic flagellates in the Southern Ocean. The presence of MNF in every ice and water sample examined suggests that mixotrophy is an important alternative dietary strategy in this region.
    Description: This work was supported by NSF grant OPP-0125833 to D.A.C. and R.J.G.
    Keywords: Ross Sea ; Antarctica ; Mixotrophy ; Mixotrophic nanoflagellates ; Bacterivory ; Plankton ; Sea ice ; Fluorescently labeled bacteria
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 5
    Publication Date: 2022-05-25
    Description: © The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Frontiers in Marine Science 5 (2018): 273, doi:10.3389/fmars.2018.00273.
    Description: Mixotrophic flagellates can comprise significant proportions of plankton biomass in marine ecosystems. Despite the growing recognition of the importance of this ecological strategy, and the identification of major environmental factors controlling phagotrophic behavior (light and nutrients), the physiological and molecular mechanisms underlying mixotrophic behavior are still unclear. In this study, we performed RNA-Seq transcriptomic analysis for two mixotrophic prasinophytes, Micromonas polaris and Pyramimonas tychotreta, under dissolved nutrient regimes that altered their ingestion of bacteria prey. Though the strains examined were polar isolates, both belong to genera with widespread distribution. Our aim was to characterize the transcriptomes of these two non-model phytoflagellates, identify transcripts consistent with phagotrophic activity and assess their differential expression in response to nutrient stress. De novo assembly of the transcriptomes yielded large numbers of novel coding transcripts with no known match within public databases. A summary of the transcripts by Gene Ontology terms showed many expected expression patterns, including genes involved in photosynthetic pathways and enzymes implicated in nutrient uptake pathways. Searches of KEGG databases identified several genes associated with intra-cellular digestive pathways actively transcribed in both prasinophytes. Differential expression analysis showed a larger response in P. tychotreta, where 23,373 genes were up-regulated and 1,752 were down-regulated in the low nutrient treatment when phagotrophy was enhanced. In contrast, in M. polaris, low nutrient treatments resulted in up-regulation of 314 transcripts while down-regulating 371. With respect to phagotrophic-related expression, 37 genes were co-expressed in both P. tychotreta and M. polaris, and although the response was less pronounced in M. polaris, it is consistent with differences in observed ingestion behavior. This study presents the first genomic data for Pyramimonas tychotreta, and also contributes to the limited available data for Micromonas polaris. Furthermore, it provides insight into the presence of genes associated with phagocytosis within the Prasinophyceae and contributes to the understanding of potential target genes required for the construction of a complete model of gene regulation of phagocytic behavior in algae.
    Description: The Owlsnest Super-Computing Cluster at Temple University is funded by a National Science Foundation Grant CNS-09-58854. The CUNY HPCC is operated by the College of Staten Island and funded, in part, by grants from the City of New York, State of New York, CUNY Research Foundation, and National Science Foundation Grants CNS-0958379, CNS-0855217, and ACI 1126113. Support for this work was also supplied by National Science Foundation grants PLR-1341362 (RG), PLR-1603538 (RS), and PLR-1603833 (RG).
    Keywords: Mixotrophy ; Pyramimonas ; Micromonas ; RNA-Seq ; Transcriptomics ; Phagotrophy
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 6
    Publication Date: 2022-09-22
    Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Grattepanche, J.-D., Jeffrey, W., Gast, R., & Sanders, R. Diversity of microbial eukaryotes along the West Antarctic Peninsula in austral spring. Frontiers in Microbiology, 13, (2022): 844856, https://doi.org/10.3389/fmicb.2022.844856.
    Description: During a cruise from October to November 2019, along the West Antarctic Peninsula, between 64.32 and 68.37°S, we assessed the diversity and composition of the active microbial eukaryotic community within three size fractions: micro- (〉 20 μm), nano- (20–5 μm), and pico-size fractions (5–0.2 μm). The communities and the environmental parameters displayed latitudinal gradients, and we observed a strong similarity in the microbial eukaryotic communities as well as the environmental parameters between the sub-surface and the deep chlorophyll maximum (DCM) depths. Chlorophyll concentrations were low, and the mixed layer was shallow for most of the 17 stations sampled. The richness of the microplankton was higher in Marguerite Bay (our southernmost stations), compared to more northern stations, while the diversity for the nano- and pico-plankton was relatively stable across latitude. The microplankton communities were dominated by autotrophs, mostly diatoms, while mixotrophs (phototrophs-consuming bacteria and kleptoplastidic ciliates, mostly alveolates, and cryptophytes) were the most abundant and active members of the nano- and picoplankton communities. While phototrophy was the dominant trophic mode, heterotrophy (mixotrophy, phagotrophy, and parasitism) tended to increase southward. The samples from Marguerite Bay showed a distinct community with a high diversity of nanoplankton predators, including spirotrich ciliates, and dinoflagellates, while cryptophytes were observed elsewhere. Some lineages were significantly related—either positively or negatively—to ice coverage (e.g., positive for Pelagophyceae, negative for Spirotrichea) and temperature (e.g., positive for Cryptophyceae, negative for Spirotrichea). This suggests that climate changes will have a strong impact on the microbial eukaryotic community.
    Description: This work was supported by the National Science Foundation (Grant Nos. ANT 1744767 to RS, ANT 1744663 to RG, and ANT 1744638 to WJ). This research was based, in part, upon sequencing conducted using the Rhode Island Genomics and Sequencing Center, which was supported in part by the National Science Foundation (MRI Grant No. DBI-0215393 and EPSCoR Grant Nos. 0554548 and EPS-1004057), the US Department of Agriculture (Grant Nos. 2002-34438-12688 and 2003-34438-13111), and the University of Rhode Island. This research includes calculations carried out on Temple University HPC resources supported in part by the National Science Foundation through major research instrumentation (Grant No. 1625061) and by the US Army Research Laboratory under (Contract No. W911NF-16-2-0189).
    Keywords: picoplankton ; nanoplankton ; microplankton ; Antarctic protists ; high-throughput sequencing ; RNA community
    Repository Name: Woods Hole Open Access Server
    Type: Article
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