Abstract
The marine roseobacter-clade affiliated cluster (RCA) represents one of the most abundant groups of bacterioplankton in the global oceans, particularly in temperate and sub-polar regions. They play a key role in the biogeochemical cycling of various elements and are important players in oceanic climate-active trace gas metabolism. In contrast to copiotrophic roseobacter counterparts such as Ruegeria pomeroyi DSS-3 and Phaeobacter sp. MED193, RCA bacteria are truly pelagic and have smaller genomes. We have previously shown that RCA bacteria do not appear to encode the PlcP-mediated lipid remodeling pathway, whereby marine heterotrophic bacteria remodel their membrane lipid composition in response to phosphorus (P) stress by substituting membrane glycerophospholipids with alternative glycolipids or betaine lipids. In this study, we report lipidomic analysis of six RCA isolates. In addition to the commonly found glycerophospholipids such as phosphatidylglycerol (PG) and phosphatidylethanolamine (PE), RCA bacteria synthesize a relatively uncommon phospholipid, acylphosphatidylglycerol, which is not found in copiotrophic roseobacters. Instead, like the abundant SAR11 clade, RCA bacteria upregulate ornithine lipid biosynthesis in response to P stress, suggesting a key role of this aminolipid in the adaptation of marine heterotrophs to oceanic nutrient limitation.
Highlights
The marine roseobacter group of Alphaproteobacteria comprises an ecologically important group of marine bacteria involved in the biogeochemical cycling of carbon, nitrogen, and sulfur (Buchan et al, 2014; Luo and Moran, 2014)
In contrast to the aforementioned strains, some marine roseobacters are truly pelagic with small genomes, which are known to be numerically abundant in marine surface waters, along with several other bacterial groups, notably the SAR11 clade (Giebel et al, 2011; Luo and Moran, 2014, 2015; Giovannoni, 2017; Sun et al, 2017)
Genome sequence and comparative genomics studies have previously shown that each roseobacter-clade affiliated cluster (RCA) strain has a unique requirement for vitamins (Voget et al, 2015; Zhang et al, 2019)
Summary
The marine roseobacter group of Alphaproteobacteria comprises an ecologically important group of marine bacteria involved in the biogeochemical cycling of carbon, nitrogen, and sulfur (Buchan et al, 2014; Luo and Moran, 2014). In contrast to the aforementioned strains, some marine roseobacters are truly pelagic with small genomes, which are known to be numerically abundant in marine surface waters, along with several other bacterial groups, notably the SAR11 clade (Giebel et al, 2011; Luo and Moran, 2014, 2015; Giovannoni, 2017; Sun et al, 2017). Three single-cell amplified genomes (SAGs) belonging to the RCA were recently reported, none of which encodes the PlcP enzyme (Sun et al, 2017) This prompted us to characterize the intact membrane lipids in this ecologically important group of pelagic marine bacteria
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