Taxonomic Comments

This genus was created to accommodate the obligately acidophilic Thiobacillus species that were shown by 16S rRNA gene sequence analysis to fall into the Gammaproteobacteria (McDonald et al., 1997; Kelly and Wood, 2000).

The assignment of T. albertis to the new genus as Acidithiobacillus albertensis is very tentative. The 16S rRNA gene sequence, required for placement in a family in the Proteobacteria, is not yet available. Its relatively high mol% G + C value (61.5) and the possession of a tuft of flagella and a glycocalyx could indicate significant differences from the other three species included here. Unfortunately, the original isolate may have been lost from culture (B.M. Goebel, personal communication).

Since the first description of Thiobacillus ferrooxidans (Temple and Colmer, 1951), numerous organisms from mineral leaching environments have been described as strains of T. ferrooxidans, because they were extremely acidophilic, obligately chemolith-oautotrophic with ferrous iron as an energy substrate, and could degrade pyrite and various other sulfide minerals. It became clear that selective culture for organisms exhibiting this growth phe-notype actually resulted in the isolation of morphologically and genomically diverse strains (Harrison, 1982; Kelly and Harrison, 1989; Kondrat'eva and Karavaiko, 1997; Goebel et al., 2000). Eight different DNA homology groups of isolates described as T. ferrooxidans were identified by Harrison (Harrison, 1982; Kelly and Harrison, 1989). One of these groups was subsequently identified as Leptospirillum, and DNA-DNA hybridization values between the group containing the type strain (ATCC 23270) and the other six groups ranged from 0-19% to 58-73%. Using PCR-based techniques to assess this genomic variability, similarity coefficients between various isolates ranged from nearly 0 to >98% (Novo et al., 1996), and while several culture collection isolates were very closely related to the type strain (ATCC 23270T), one

TABLE BXII.y.16. Basic characteristics of species of the genus Acidithiobacillus


1. A. thiooxidans

2. A. albertensis

3. A. caldus

4. A. ferrooxidans

Mol% G + C

0 0

Post a comment