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Identification of Associations between Bacterioplankton and Photosynthetic Picoeukaryotes in Coastal Waters.

Farnelid HM, Turk-Kubo KA, Zehr JP - Front Microbiol (2016)

Bottom Line: Photosynthetic picoeukaryotes are significant contributors to marine primary productivity.The results show that diverse bacterial phylotypes are found in association with photosynthetic picoeukaryotes.Taxonomic identification of these associations is a prerequisite for further characterizing and to elucidate their metabolic pathways and ecological functions.

View Article: PubMed Central - PubMed

Affiliation: Ocean Sciences Department, University of California at Santa CruzSanta Cruz, CA, USA; Centre for Ecology and Evolution in Microbial Model Systems, Linnaeus UniversityKalmar, Sweden.

ABSTRACT
Photosynthetic picoeukaryotes are significant contributors to marine primary productivity. Associations between marine bacterioplankton and picoeukaryotes frequently occur and can have large biogeochemical impacts. We used flow cytometry to sort cells from seawater to identify non-eukaryotic phylotypes that are associated with photosynthetic picoeukaryotes. Samples were collected at the Santa Cruz wharf on Monterey Bay, CA, USA during summer and fall, 2014. The phylogeny of associated microbes was assessed through 16S rRNA gene amplicon clone and Illumina MiSeq libraries. The most frequently detected bacterioplankton phyla within the photosynthetic picoeukaryote sorts were Proteobacteria (Alphaproteobacteria and Gammaproteobacteria) and Bacteroidetes. Intriguingly, the presence of free-living bacterial genera in the photosynthetic picoeukaryote sorts could suggest that some of the photosynthetic picoeukaryotes were mixotrophs. However, the occurrence of bacterial sequences, which were not prevalent in the corresponding bulk seawater samples, indicates that there was also a selection for specific OTUs in association with photosynthetic picoeukaryotes suggesting specific functional associations. The results show that diverse bacterial phylotypes are found in association with photosynthetic picoeukaryotes. Taxonomic identification of these associations is a prerequisite for further characterizing and to elucidate their metabolic pathways and ecological functions.

No MeSH data available.


Contributions of the most frequently occurring eukaryotic phyla among chloroplast sequences detected in each of the sorted photosynthetic picoeukaryote samples (1,000 P1 cells, triplicate samples) and the corresponding seawater samples (0.2–10 μm) for each sampling date. The percentage of chloroplast sequences within each library is indicated to the right of each bar.
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Figure 4: Contributions of the most frequently occurring eukaryotic phyla among chloroplast sequences detected in each of the sorted photosynthetic picoeukaryote samples (1,000 P1 cells, triplicate samples) and the corresponding seawater samples (0.2–10 μm) for each sampling date. The percentage of chloroplast sequences within each library is indicated to the right of each bar.

Mentions: 16S rRNA gene amplicons from triplicate samples of 1,000 photosynthetic picoeukaryote cell sorts (P1) and the corresponding bulk seawater samples from five sampling occasions were sequenced (Table 3). The composition of OTUs among the triplicate sorts were more similar to each other compared to samples from a different day but the adjacent sampling dates October 15, October 22, and October 29 showed high Bray–Curtis similarity (>80%; Figure 3A). Most of the sequences in the photosynthetic picoeukaryote sort samples were plastid (Figure 4). A large cluster of OTUs were 96–100% identical to Micromonas pusilla and these sequences were most frequently detected in all sorted samples (accounting for between 75–96% of chloroplast sequences). Micromonas, a marine prasinophyte within the order Mamiellales, are known to be diverse and globally distributed (Guillou et al., 2004; Worden et al., 2009). Bathycoccus prasinos and Ostreococcus tauri OTUs were also detected in all samples. Notably, at lower relative abundances in the summer sample compared to the fall samples (Figure 4). In comparison to the sorted samples, the chloroplast sequences from bulk seawater were more diverse and not solely dominated by Chlorophyta. For example, in the bulk seawater samples, Haptophytes and Stramenopiles were present at high relative abundances (18–24%) while these phyla composed <10% in all of the sorted samples. The photosynthetic picoeukaryote populations were sorted based on chlorophyll a content and size. Thereby larger eukaryotes (∼ >3 μm beads) as well as heterotrophic picoeukaryotes would be excluded unless they had attached or ingested chlorophyll a containing cells. Thus, a difference in composition and a greater diversity of eukaryotic cells was expected in the bulk seawater samples compared to the sorted samples (Figures 3A and 4).


Identification of Associations between Bacterioplankton and Photosynthetic Picoeukaryotes in Coastal Waters.

Farnelid HM, Turk-Kubo KA, Zehr JP - Front Microbiol (2016)

Contributions of the most frequently occurring eukaryotic phyla among chloroplast sequences detected in each of the sorted photosynthetic picoeukaryote samples (1,000 P1 cells, triplicate samples) and the corresponding seawater samples (0.2–10 μm) for each sampling date. The percentage of chloroplast sequences within each library is indicated to the right of each bar.
© Copyright Policy
Related In: Results  -  Collection

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Figure 4: Contributions of the most frequently occurring eukaryotic phyla among chloroplast sequences detected in each of the sorted photosynthetic picoeukaryote samples (1,000 P1 cells, triplicate samples) and the corresponding seawater samples (0.2–10 μm) for each sampling date. The percentage of chloroplast sequences within each library is indicated to the right of each bar.
Mentions: 16S rRNA gene amplicons from triplicate samples of 1,000 photosynthetic picoeukaryote cell sorts (P1) and the corresponding bulk seawater samples from five sampling occasions were sequenced (Table 3). The composition of OTUs among the triplicate sorts were more similar to each other compared to samples from a different day but the adjacent sampling dates October 15, October 22, and October 29 showed high Bray–Curtis similarity (>80%; Figure 3A). Most of the sequences in the photosynthetic picoeukaryote sort samples were plastid (Figure 4). A large cluster of OTUs were 96–100% identical to Micromonas pusilla and these sequences were most frequently detected in all sorted samples (accounting for between 75–96% of chloroplast sequences). Micromonas, a marine prasinophyte within the order Mamiellales, are known to be diverse and globally distributed (Guillou et al., 2004; Worden et al., 2009). Bathycoccus prasinos and Ostreococcus tauri OTUs were also detected in all samples. Notably, at lower relative abundances in the summer sample compared to the fall samples (Figure 4). In comparison to the sorted samples, the chloroplast sequences from bulk seawater were more diverse and not solely dominated by Chlorophyta. For example, in the bulk seawater samples, Haptophytes and Stramenopiles were present at high relative abundances (18–24%) while these phyla composed <10% in all of the sorted samples. The photosynthetic picoeukaryote populations were sorted based on chlorophyll a content and size. Thereby larger eukaryotes (∼ >3 μm beads) as well as heterotrophic picoeukaryotes would be excluded unless they had attached or ingested chlorophyll a containing cells. Thus, a difference in composition and a greater diversity of eukaryotic cells was expected in the bulk seawater samples compared to the sorted samples (Figures 3A and 4).

Bottom Line: Photosynthetic picoeukaryotes are significant contributors to marine primary productivity.The results show that diverse bacterial phylotypes are found in association with photosynthetic picoeukaryotes.Taxonomic identification of these associations is a prerequisite for further characterizing and to elucidate their metabolic pathways and ecological functions.

View Article: PubMed Central - PubMed

Affiliation: Ocean Sciences Department, University of California at Santa CruzSanta Cruz, CA, USA; Centre for Ecology and Evolution in Microbial Model Systems, Linnaeus UniversityKalmar, Sweden.

ABSTRACT
Photosynthetic picoeukaryotes are significant contributors to marine primary productivity. Associations between marine bacterioplankton and picoeukaryotes frequently occur and can have large biogeochemical impacts. We used flow cytometry to sort cells from seawater to identify non-eukaryotic phylotypes that are associated with photosynthetic picoeukaryotes. Samples were collected at the Santa Cruz wharf on Monterey Bay, CA, USA during summer and fall, 2014. The phylogeny of associated microbes was assessed through 16S rRNA gene amplicon clone and Illumina MiSeq libraries. The most frequently detected bacterioplankton phyla within the photosynthetic picoeukaryote sorts were Proteobacteria (Alphaproteobacteria and Gammaproteobacteria) and Bacteroidetes. Intriguingly, the presence of free-living bacterial genera in the photosynthetic picoeukaryote sorts could suggest that some of the photosynthetic picoeukaryotes were mixotrophs. However, the occurrence of bacterial sequences, which were not prevalent in the corresponding bulk seawater samples, indicates that there was also a selection for specific OTUs in association with photosynthetic picoeukaryotes suggesting specific functional associations. The results show that diverse bacterial phylotypes are found in association with photosynthetic picoeukaryotes. Taxonomic identification of these associations is a prerequisite for further characterizing and to elucidate their metabolic pathways and ecological functions.

No MeSH data available.