The replacement of ethanol by formate reversed the domination in selleckchem favor of the vibrio morphotype and eventually resulted in the isolation

of the extremely natronophilic SRB strain AHT8 described previously as Desulfonatronospira thiodismutans (Sorokin et al., 2008). The curved rods were purified from single colonies on the original medium with ethanol and thiosulfate and the resulting strain was designated AHT5. A similar strain, ASP-p, was obtained from another Kulunda lake enrichment at 2 M Na+ and pH 10 with formate/acetate as an electron donor/carbon source and thiosulfate as an electron acceptor. In that case, the enrichment was dominated by the SRB Desulfonatronovibrio sp., while the curved rods became dominant after the replacement of formate/acetate with pyruvate. According to 16S rRNA gene sequence analysis, both rod-shaped

isolates were very close to each other and to Tindallia magadiensis (99% sequence similarity), which was found previously in the hypersaline soda lake Magadi (Kenya) and described as an obligately heterotrophic haloalkaliphilic acetogen preferentially fermenting amino acids (Kevbrin et al., 1998). DNA–DNA hybridization showed that the novel isolates were nearly identical (around 95% DNA similarity) and belonged to T. magadiensis species (85% DNA hybridization HKI-272 mouse value with the type strain). However, despite this

close relation, anaerobic respiration has not been demonstrated previously in the genus Tindallia, except for the ability to reduce ferric iron, which was not coupled to growth in T. magadiensis and Tindallia texcoconensis (Kevbrin et al., 1998; Alazard et al., 2007). Examination of the type species T. magadiensis confirmed the absence of growth by thiosulfate respiration in this organism. There were two ecologically important differences of Tindallia sp. strains AHT5 and ASP-p from the previously described acetogenic Tindallia tuclazepam species. First, they both grew lithoautotrophically with H2 and formate. Second, they were capable of true anaerobic respiration with H2, formate, pyruvate, lactate and glycerol as electron donors using thiosulfate, sulfur or fumarate as an electron acceptor (Table 1). Interestingly, formate was detected as a product of anaerobic H2 metabolism instead of acetate, which is expected for an acetogen. It might be speculated that formate in this case is a product of reversed formate lyase reaction, but the significance of its formation is not clear and needs further investigation. Recently, a possibility of anaerobic growth by the opposite reaction (conversion of formate to H2) has been demonstrated for a thermophilic archaeon (Kim et al., 2010) and for syntrophic cultures of acetogens and methanogens (Dolfing et al., 2008).