Alkaliphilic sulfur-oxidizing bacteria were isolated from an alkaliphilic microbial consortium used to treat H2S at pH>9 in a laboratory scale biofilter. Nineteen isolates were obtained. These isolates could be grouped based on their colonial morphology on a solid medium containing thiosulfate as sole energy source. Half of the isolates presented yellow colonies (group I). This yellowish colonial morphology is typically found in the genus Thioalkalivibrio. For the rest of the isolates, the colonies were white (group II) or transparent (group III). The isolates of each group were characterized by ribosomal intergenic spacer analysis and restriction analysis of their 16S rRNA genes. One of the yellow isolates presented 85% of homology with Thioalkalivibrio jannaschii by partial sequencing of its 16S rRNA gene. The genus Thioalkalivibrio comprises extremely haloalkaliphilic sulfur-oxidizing bacteria that have been proposed as suitable biocatalysts for natural gas desulfurization.