Comparative analysis of 16S rRNA gene sequences, DNA–DNA hybridization data and phenotypic properties revealed that ‘Sulfobacillus thermosulfidooxidans subsp. thermotolerans’ strain K1 is not a member of the genus Sulfobacillus. Phylogenetically, strain K1 is closely related to unclassified strains of the genus Alicyclobacillus: the 16S rRNA gene sequence of strain K1 is similar to that of Alicyclobacillus sp. AGC-2 (99·6 %), Alicyclobacillus sp. 5C (98·9 %) and Alicyclobacillus sp. CLG (98·6 %) and bacterium GSM (99·1 %). The 16S rRNA gene sequence similarity values for strain K1 and species of the genus Alicyclobacillus with validly published names were in the range 92·1–94·6 %, and for S. thermosulfidooxidans VKM B-1269T the value was 87·7 %. Sulfobacillus disulfidooxidans SD-11T was also phylogenetically related to strain K1 (92·6 % sequence similarity) and thus belonged to the genus Alicyclobacillus. Chemotaxonomic data, such as the major cell-membrane lipid components of strains K1 and SD-11T (ω-alicyclic fatty acids) and the major isoprenoid quinone (menaquinone MK-7) of strain K1, supported the affiliation of strains K1 and SD-11T to the genus Alicyclobacillus. Physiological and molecular biological tests allowed genotypic and phenotypic differentiation of strains K1 and SD-11T from the nine Alicyclobacillus species with validly published names. The G+C content of the DNA of strain K1 was 48·7±0·6 mol%; that of strain SD-11T was 53±1 mol%. DNA–DNA reassociation studies showed low relatedness (22 %) between strains K1 and SD-11T, and even lower relatedness (3–5 %) between these strains and Alicyclobacillus acidocaldarius subsp. acidocaldarius ATCC 27009T, DSM 446T. DNA reassociation of strains K1 and SD-11T with Alicyclobacillus cycloheptanicus DSM 4006T gave values of 15 and 21, respectively. Based on the phenotypic and phylogenetic characteristics of strains K1 and SD-11T, Alicyclobacillus tolerans sp. nov. (type strain, K1T=VKM B-2304T=DSM 16297T) and Alicyclobacillus disulfidooxidans comb. nov. (type strain, SD-11T=ATCC 51911T=DSM 12064T) are proposed.

A thermotolerant, Gram-positive, aerobic, endospore-forming, acidophilic bacterium (strain Kr1 T )was isolated from the pulp of a gold-containing sulfide concentrate processed at 40 6C in a gold-recovery plant (Siberia

The first complete genome of the biotechnologically important species Sulfobacillus thermotolerans has been sequenced. Its 3 317 203-bp chromosome contains an 83 269-bp plasmid-like region, which carries heavy metal resistance determinants and the rusticyanin gene. Plasmid-mediated metal resistance is unusual for acidophilic chemolithotrophs. Moreover, most of their plasmids are cryptic and do not contribute to the phenotype of the host cells. A polyphosphate-based mechanism of metal resistance, which has been previously unknown in the genus Sulfobacillus or other Gram-positive chemolithotrophs, potentially operates in two Sulfobacillus species. The methylcitrate cycle typical for pathogens and identified in the genus Sulfobacillus for the first time can fulfill the energy and/or protective function in S. thermotolerans Kr1 and two other Sulfobacillus species, which have incomplete glyoxylate cycles. It is notable that the TCA cycle, disrupted in all Sulfobacillus isolates under optimal growth conditions, proved to be complete in the cells enduring temperature stress. An efficient antioxidant defense system gives S. thermotolerans another competitive advantage in the microbial communities inhabiting acidic metal-rich environments. The genomic comparisons revealed 80 unique genes in the strain Kr1, including those involved in lactose/galactose catabolism. The results provide new insights into metabolism and resistance mechanisms in the Sulfobacillus genus and other acidophiles.

The communities of acidophilic chem olithotrophic microorganisms (ACM) are formed in sulfide ore deposits, mine waters, pyrite coals, the wastes of ore mining and processing industry in differ ent geographical and climatic zones, as well as in the pulps of reactors for the technologies of bacterialchemical oxidation of sulfide ore concentrates, i.e., in the presence of sulfide minerals and their oxidation products, elemental sulfur, reduced sulfur com pounds, and ferrous iron. As a result of their activity, the medium is acidified, sometimes to pH 0.5 or less, and the concentrations of heavy metals and toxic ele ments (copper, zinc, nickel, cobalt, arsenic, etc.) increase. These microorganisms therefore belong to extreme chemolithotrophic acidophiles. They include representatives of bacteria (both gram negative and gram positive) and archaea.Tables 1-3 present the best studied and most fre quently occurring ACM, the substrates they oxidize, and the ranges and optimal values of pH and tempera ture for their growth . It can be seen that some microorganisms can oxidize all inorganic substrates mentioned above, e.g., gram negative bacteria of the genus Acidithiobacillus (At. ferrooxidans, At. fer rivorans), gram positive bacteria of the genus Sulfoba cillus (S. thermosulfidooxidans, S. thermotolerans, S. benefaciens), and the archaeon Acidianus (Ac.) bri erleyi. Ferrous iron, elemental sulfur and sulfide min erals are used as energy sources by Metallosphaera sedula and M. prunae. Other microorganisms can obtain energy by oxidizing only ferrous iron or pyrite: Leptospirillum ferrooxidans, L. ferriphilum, and Ferro plasma acidiphilum. Most of the microorganisms (At. thiooxidans, At. caldus, and archaea) use elemen tal sulfur and reduced sulfur compounds as an energy substrate. The pH optima for the growth of these microorganisms are different, but all of them are in the range of acidic values. ACM live in a broad tempera ture range of 4 to 90°С. They include mesophiles with the optimal temperature for growth and oxidation of the energy substrate in the range of 28-35°С, moder ate thermophiles with the temperature optimum at 40 to 55°С, and thermophiles with the temperature opti mum above 60°С. The latter include mainly archaea. For instance, Ac. infernus has a temperature optimum for growth at 90°С [20].Abstract-The main representatives of acidophilic chemolithotrophs oxidizing sulfide minerals, ferrous iron, elemental sulfur, and reduced sulfur compounds and forming microbial communities in the natural and technogenic ecosystems with low pH values and high concentrations of heavy metal ions are listed. The spe cies and strain diversity of the communities and environmental factors affecting their composition (temper ature, pH value, energy substrate, mineralogical composition of sulfide ore concentrates, the presence of organic substances, and level of aeration) are analyzed. Involvement of mobile genetic elements (IS elements and plasmids) in the structural changes of the chromosomal DNA in the course of switching m...

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