title: Substrate-level phosphorylation is the primary source of energy conservation during anaerobic respiration of Shewanella oneidensis strain MR-1.
abstract: It is well established that respiratory organisms use proton motive force to produce ATP via F-type ATP synthase aerobically and that this process may reverse during anaerobiosis to produce proton motive force. Here, we show that Shewanella oneidensis strain MR-1, a nonfermentative, facultative anaerobe known to respire exogenous electron acceptors, generates ATP primarily from substrate-level phosphorylation under anaerobic conditions. Mutant strains lacking ackA (SO2915) and pta (SO2916), genes required for acetate production and a significant portion of substrate-level ATP produced anaerobically, were tested for growth. These mutant strains were unable to grow anaerobically with lactate and fumarate as the electron acceptor, consistent with substrate-level phosphorylation yielding a significant amount of ATP. Mutant strains lacking ackA and pta were also shown to grow slowly using N-acetylglucosamine as the carbon source and fumarate as the electron acceptor, consistent with some ATP generation deriving from the Entner-Doudoroff pathway with this substrate. A deletion strain lacking the sole F-type ATP synthase (SO4746 to SO4754) demonstrated enhanced growth on N-acetylglucosamine and a minor defect with lactate under anaerobic conditions. ATP synthase mutants grown anaerobically on lactate while expressing proteorhodopsin, a light-dependent proton pump, exhibited restored growth when exposed to light, consistent with a proton-pumping role for ATP synthase under anaerobic conditions. Although S. oneidensis requires external electron acceptors to balance redox reactions and is not fermentative, we find that substrate-level phosphorylation is its primary anaerobic energy conservation strategy. Phenotypic characterization of an ackA deletion in Shewanella sp. strain MR-4 and genomic analysis of other sequenced strains suggest that this strategy is a common feature of Shewanella.
authors.affiliation: BioTechnology Institute, University of Minnesota, 140 Gortner Lab, 1479 Gortner Ave., St. Paul, MN 55108, USA.
authors.forename: Kristopher A
authors.initials: KA
authors.lastname: Hunt
authors.forename: Jeffrey M
authors.initials: JM
authors.lastname: Flynn
authors.forename: Belén
authors.initials: B
authors.lastname: Naranjo
authors.forename: Indraneel D
authors.initials: ID
authors.lastname: Shikhare
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Gralnick
mesh_terms: D000693:Anaerobiosis; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D005816:Genetic Complementation Test; D008954:Models, Biological; D009154:Mutation; D010766:Phosphorylation; D020592:Shewanella / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins
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