Thioalkalivibrio sulfidiphilus sp. nov., a haloalkaliphilic, sulfur-oxidizing gammaproteobacterium from alkaline habitats

Abstract

A moderately salt-tolerant and obligately alkaliphilic, chemolithoautotrophic sulfur-oxidizing bacterium, strain HL-EbGr7T, was isolated from a full-scale bioreactor removing H2S from biogas under oxygen-limited conditions. Another strain, ALJ17, closely related to HL-EbGr7T, was isolated from a Kenyan soda lake. Cells of the isolates were relatively long, slender rods, motile by a polar flagellum. Although both strains were obligately aerobic, micro-oxic conditions were preferred, especially at the beginning of growth. Chemolithoautotrophic growth was observed with sulfide and thiosulfate in a pH range of 8.0–10.5 (optimum at pH 10.0) and a salinity range of 0.2–1.5 M total Na+ (optimum at 0.4 M). The genome sequence of strain HL-EbGr7T demonstrated the presence of genes encoding the reverse Dsr pathway and a truncated Sox pathway for sulfur oxidation and enzymes of the Calvin–Benson cycle of autotrophic CO2 assimilation with ribulose-bisphosphate carboxylase/oxygenase (RuBisCO) type I. The dominant cellular fatty acids were C18 : 1ω7, C16 : 0 and C19 : 0 cyclo. Based on 16S rRNA gene sequencing, the two strains belonged to a single phylotype within the genus Thioalkalivibrio in the Gammaproteobacteria . Despite being related most closely to Thioalkalivibrio denitrificans , the isolates were unable to grow by denitrification. On the basis of phenotypic and phylogenetic analysis, the novel isolates are proposed to represent a novel species, Thioalkalivibrio sulfidiphilus sp. nov., with the type strain HL-EbGr7T ( = NCCB 100376T  = UNIQEM U246T).