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FEMS Microbiol Ecol. 2016 Dec;92(12). pii: fiw199. Epub 2016 Sep 21.

Genomic insights into metabolic versatility of a lithotrophic sulfur-oxidizing diazotrophic Alphaproteobacterium Azospirillum thiophilum.

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Department of Cell Biochemistry and Cell Physiology, Voronezh State University, Voronezh 394018, Russia.
All-Russian Collection of Microorganisms (VKM), G.K. Skryabin Institute of Biochemistry and Physiology of Microorganisms, Russian Academy of Sciences, Pushchino 142290, Moscow Region, Russia.
Federal State Institution "Federal Research Centre "Fundamentals of Biotechnology" of the Russian Academy of Sciences" Moscow 117312, Russia.
Institute of Cell Biophysics, Russian Academy of Sciences, Institutskaya street 3, Pushchino 142290, Moscow, Russia.
Department of Cell Biochemistry and Cell Physiology, Voronezh State University, Voronezh 394018, Russia


Diazotrophic Alphaproteobacteria of the genus Azospirillum are usually organotrophs, although some strains of Azospirillum lipoferum are capable of hydrogen-dependent autotrophic growth. Azospirillum thiophilum strain was isolated from a mineral sulfide spring, a biotope highly unusual for azospirilla. Here, the metabolic pathways utilized by A. thiophilum were revealed based on comprehensive analysis of its genomic organization, together with physiological and biochemical approaches. The A. thiophilum genome contained all the genes encoding the enzymes of carbon metabolism via glycolysis, tricarboxylic acid cycle and glyoxylate cycle. Genes for a complete set of enzymes responsible for autotrophic growth, with an active Calvin-Benson-Bassham cycle, were also revealed, and activity of the key enzymes was determined. Microaerobic chemolithoautotrophic growth of A. thiophilum was detected in the presence of thiosulfate and molecular hydrogen, being in line with the discovery of the genes encoding the two enzymes involved in dissimilatory thiosulfate oxidation, the Sox-complex and thiosulfate dehydrogenase and Ni-Fe hydrogenases. Azospirillum thiophilum utilizes methanol and formate, producing CO2 that can further be metabolized via the Calvin cycle. Finally, it is capable of anaerobic respiration, using tetrathionate as a terminal electron acceptor. Such metabolic versatility is of great importance for adaptation of A. thiophilum to constantly changing physicochemical environment.


Azospirillum thiophilum; autotrophy; complete genome; genome analysis; metabolic reconstruction; metabolic versatility; methylotrophic growth

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