title: One carbon metabolism in SAR11 pelagic marine bacteria.
abstract: The SAR11 Alphaproteobacteria are the most abundant heterotrophs in the oceans and are believed to play a major role in mineralizing marine dissolved organic carbon. Their genomes are among the smallest known for free-living heterotrophic cells, raising questions about how they successfully utilize complex organic matter with a limited metabolic repertoire. Here we show that conserved genes in SAR11 subgroup Ia (Candidatus Pelagibacter ubique) genomes encode pathways for the oxidation of a variety of one-carbon compounds and methyl functional groups from methylated compounds. These pathways were predicted to produce energy by tetrahydrofolate (THF)-mediated oxidation, but not to support the net assimilation of biomass from C1 compounds. Measurements of cellular ATP content and the oxidation of (14)C-labeled compounds to (14)CO(2) indicated that methanol, formaldehyde, methylamine, and methyl groups from glycine betaine (GBT), trimethylamine (TMA), trimethylamine N-oxide (TMAO), and dimethylsulfoniopropionate (DMSP) were oxidized by axenic cultures of the SAR11 strain Ca. P. ubique HTCC1062. Analyses of metagenomic data showed that genes for C1 metabolism occur at a high frequency in natural SAR11 populations. In short term incubations, natural communities of Sargasso Sea microbial plankton expressed a potential for the oxidation of (14)C-labeled formate, formaldehyde, methanol and TMAO that was similar to cultured SAR11 cells and, like cultured SAR11 cells, incorporated a much larger percentage of pyruvate and glucose (27-35%) than of C1 compounds (2-6%) into biomass. Collectively, these genomic, cellular and environmental data show a surprising capacity for demethylation and C1 oxidation in SAR11 cultures and in natural microbial communities dominated by SAR11, and support the conclusion that C1 oxidation might be a significant conduit by which dissolved organic carbon is recycled to CO(2) in the upper ocean.
authors: Department of Microbiology, Oregon State University, Corvallis, Oregon, United States of America.
authors: Jing
authors: J
authors: Sun
authors: Laura
authors: L
authors: Steindler
authors: J Cameron
authors: JC
authors: Thrash
authors: Kimberly H
authors: KH
authors: Halsey
authors: Daniel P
authors: DP
authors: Smith
authors: Amy E
authors: AE
authors: Carter
authors: Zachary C
authors: ZC
authors: Landry
authors: Stephen J
authors: SJ
authors: Giovannoni
mesh_terms: D020561:Alphaproteobacteria / Q000378:metabolism*; D059001:Aquatic Organisms / Q000378:metabolism*; D002244:Carbon / Q000378:metabolism*; D002245:Carbon Dioxide; D008745:Methylation; D010100:Oxygen / Q000378:metabolism; D014871:Water Microbiology
chemical_list: D002245:Carbon Dioxide; D002244:Carbon; D010100:Oxygen