Polish Journal of Microbiology 2014, Vol. 63, No 2, 245–247 SHORT COMMUNICATION * Corresponding author: D.P. Kelly, School of Life Sciences, University of Warwick, Coventry CV4 7AL, UK; e-mail: D.P.Kelly@ warwick.ac.uk hermithiobacillus tepidarius is an obligately aero- bic, moderately thermophilic, neutrophilic, obligately chemolithotrophic proteobacterium, initially classified as a strain of the betaproteobacterial genus hiobacillus on the basis of its morphology and biochemistry (Wood and Kelly, 1985, 1986). It was subsequently redefined as the type species of the genus hermithiobacillus (Kelly and Wood, 2000), and the type (and only) genus of the family hermithiobacillaceae. his family was created using the proteobacterial phylogeny based on 16S ribo- somal RNA gene sequencing employed for the 2 nd  edi- tion of Bergey’s Manual of Systematic Bacteriology (Gar- rity, Bell and Lilburn, 2005; Kelly and Wood, 2014a). It became Family II of the order Acidithiobacillales in the Gammaproteobacteria (Garrity, Bell and Lilburn, 2005). he earliest study of 16S rRNA relationships among sulfur-oxidizing chemolithotrophs, using a par- tial sequence for hermithiobacillus tepidarius, placed it midway between hiobacillus neapolitanus and the extremely acidiphilic hiobacillus thiooxidans in terms of evolutionary distances (Lane et al., 1992)). he adop- tion of 16S rRNA gene sequence analysis as a major phylogenetic tool led to the reclassification of numer- ous species of hiobacillus into a range of new genera, including hermithiobacillus, or assignment to existing genera such as hiomonas, Paracoccus and Acidiphilium (Kelly and Wood, 2000, 2005, 2014a, b; Kelly, Wood and Stackebrandt, 2005). While T. tepidarius was physi- ologically more like neutrophilic species of hiobacil- lus, Halothiobacillus, and hiomicrospira, or even the thermophile hermothrix, its 16S rRNA gene sequence shared only 85% identity with that of hiobacillus thioparus, 82–85% with Halothiobacllus neapolitanus, H. halophilus, and H. kellyi, 79% with hiomicrospira crunogena, and 74–79% with hermothrix thiopara and Tx. azorensis, unequivocally excluding it from those genera. he least distant phylogenetic relatives of hermithiobacillus tepidarius are Acidithiobacillus spe- cies (comprising Family I, the Acidithiobacillaceae, of the Acidithiobacillales), with 90–91% 16S rRNA gene sequence identity to At. thiooxidans and At. ferrooxidans. On the basis of nearest-neighbour 16S rRNA relation- ship, the parent order for hermithiobacillus was the Acidithiobacillales, but it difered from these acidophiles in being thermophilic and neutrophilic, with only Acidi- thiobacillus caldus also being moderately thermophilic (Kelly and Wood, 2014b). It is not uncommon to find diferences among 16s rRNA gene sequences of spe- cies of the same genus or family: for example, the range among Halothiobacillus species is 91–99% identity, but Definitive Assignment by Multigenome Analysis of the Gammaproteobacterial Genus hermithiobacillus to the Class Acidithiobacillia COREY M. HUDSON 1 , KELLY P. WILLIAMS 1 and DONOVAN P. KELLY 2, * 1 Systems Biology Department, Sandia National Laboratories, Livermore, CA 94551, USA 2 School of Life Sciences, University of Warwick, Coventry CV4 7AL, UK Submitted 13 March 2014, accepted 14 April 2014 Abstract he class Acidithiobacillia was established using multiprotein phylogenetic analysis of all the available genomes of the genus Acidithiobacillus (comprising Family I, the Acidithiobacillaceae, of the Acidithiobacillales, the order created for Bergey’s Manual of Systematic Bacteriology), and for representative genomes of all available bacterial orders. he Acidithiobacillales contain a second family, the hermithiobacillaceae, represented by hermithiobacillus tepidarius, and created on the basis of nearest neighbour 16S ribosomal RNA gene sequence similarities. his could not be included in the original multiprotein analysis as no genome sequence for hermithiobacillus was available. he publica- tion of the genome sequence of hermithiobacillus tepidarius in 2013 has enabled phylogenetic assessment of this organism by comparative multigenome analysis. his shows definitively that hermithiobacillus is a member of the class Acidithiobacillia, distinct from the Acidi- thiobacillus genus, and confirms it to represent a second family within the Acidithiobacillia. Key words: hermithiobacillus, Acidithiobacillus, Acidithiobacillia, multigenome phylogeny; multiprotein analysis