Two new species of microaerophilic sulfur spirilla, Spirillum winogradskii sp. nov. and Spirillum kriegii sp. nov.

Abstract

New microaerophilic sulfur-oxidizing spirilla were isolated from hydrogen sulfide sludge of wastewater treatment plants. Strains D-427 and D-430 have spiral cells that are highly motile due to bipolar flagellum bundles covered with mucous sheaths. Under a phase-contrast microscope, these bundles are visible as single polar flagella. Spheroplasts are formed in the stationary growth phase. Both strains are obligate organotrophs able to oxidize a number of reduced sulfur compounds. The oxidation of sulfide and polysulfide leads to the formation of intracellular globules of elemental sulfur; thiosulfate oxidation results in tetrathionate accumulation in the medium. The cells are unable to utilize reduced sulfur compounds in the energy metabolism; their oxidation is caused by a chemical interaction with H2O2 and O2, synthesized in the electron transport chain. Both strains are obligate microaerophiles with an optimal oxygen concentration in the gas phase of 2 and 0.8% for strains D-427 and D-430, respectively. The strains utilize a limited number of organic acids as growth substrates, mainly tricarboxylic-acid-cycle intermediates. The DNA G+C content is 38.0 mol % (T(m)) for strain D-427 and 38.9 mol % for strain D-430. Phylogenetic analysis, based on the comparison of 16S rRNA gene sequences, revealed that the new isolates of sulfur spirilla are the most closely related to Spirillum volutans, the type species of the genus (97.4% similarity). They were assigned to the genus Spirillum within the class Beta-proteobacteria as two new species, S. winogradskii sp. nov. (D-427T = DSM 12756T) and S. kriegii sp. nov. (B-430T = BKM B-2372T). The emended description of the genus Spirillum is provided.