Taxonomic Comments

The family Halothiobacillaceae has been newly created to include the single genus Halothiobacillus, and the characteristics of the family are currently those given in the Genus Halothiobacillus chapter.

The four currently recognized and validly published species are physiologically and morphologically similar, and exhibit a relatively wide spread of mol% G + C content of their DNA. Their distinctive physiological properties and biochemical requirements distinguish them all other species. Analysis of nearly complete 16S rDNA sequences from all four species showed them to form a single phylogenetic cluster (Kelly et al., 1998; Kelly and Wood, 2000; Sievert et al., 2000).

Pairwise comparisons of the relative identities of their 16S rDNA sequences using BLASTN and BLAST2 (http://www.ncbi. showed the type species, H. neapolitanus, to share 91.092.9% identity with the other three; H. kellyi showed 93.4% identity to both H. halophilus and H. hydrothermalis; and H. halophilus and H. hydrothermalis shared 98.6% identity. For comparison, 16S rDNA from Albchromatium vinosum ATCC 17899 (M26629) showed only 86.7% and 88.0% identity to H. neapolitanus and H. halophilus. Several other strains of Halothiobacillus have been identified by 16S rDNA sequencing (strains MS02, RA13, W5 and WJ18), and additional species are likely to be defined and validly published in due course.

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