| Abstract |
- Bacterioplankton of the SAR11 clade are the most abundant microorganisms in marine systems,
usually representing 25% or more of the total bacterial cells in seawater worldwide. SAR11 is divided
into subclades with distinct spatiotemporal distributions (ecotypes), some of which appear to be
specific to deep water. Here we examine the genomic basis for deep ocean distribution of one SAR11
bathytype (depth-specific ecotype), subclade Ic. Four single-cell Ic genomes, with estimated
completeness of 55%–86%, were isolated from 770 m at station ALOHA and compared with eight
SAR11 surface genomes and metagenomic datasets. Subclade Ic genomes dominated metagenomic
fragment recruitment below the euphotic zone. They had similar COG distributions, high local
synteny and shared a large number (69%) of orthologous clusters with SAR11 surface genomes, yet
were distinct at the 16S rRNA gene and amino-acid level, and formed a separate, monophyletic
group in phylogenetic trees. Subclade Ic genomes were enriched in genes associated with
membrane/cell wall/envelope biosynthesis and showed evidence of unique phage defenses.
The majority of subclade Ic-specfic genes were hypothetical, and some were highly abundant in
deep ocean metagenomic data, potentially masking mechanisms for niche differentiation. However,
the evidence suggests these organisms have a similar metabolism to their surface counterparts, and
that subclade Ic adaptations to the deep ocean do not involve large variations in gene content, but
rather more subtle differences previously observed deep ocean genomic data, like preferential
amino-acid substitutions, larger coding regions among SAR11 clade orthologs, larger intergenic
regions and larger estimated average genome size.
- Keywords: Metagenomics, Bathytype, Deep ocean, SAR11, Ecotype, Single-cell genomics
- Keywords: Metagenomics, Bathytype, Deep ocean, SAR11, Ecotype, Single-cell genomics
- Keywords: Metagenomics, Bathytype, Deep ocean, SAR11, Ecotype, Single-cell genomics
- Keywords: Metagenomics, Bathytype, Deep ocean, SAR11, Ecotype, Single-cell genomics
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