An isolate of an acidophilic archaeon, strain Y T , was obtained from a bioleaching pilot plant. The organism oxidizes ferrous iron as the sole energy source and fixes inorganic carbon as the sole carbon source. The optimal pH for growth is 17, although growth is observed in the range pH 13 to 22. The cells are pleomorphic and without a cell wall. 16S rRNA gene sequence analysis showed this strain to cluster phylogenetically within the order ' Thermoplasmales ' sensu Woese, although with only 899 and 872 % sequence identity, respectively, to its closest relatives, Picrophilus oshimae and Thermoplasma acidophilum. Other principal differences from described species of the ' Thermoplasmales ' are autotrophy (strain Y T is obligately autotrophic), the absence of lipid components typical of the ' Thermoplasmales ' (no detectable tetraethers) and a lower temperature range for growth (growth of strain Y T occurs between 15 and 45 SC). None of the sugars, amino acids, organic acids or other organic compounds tested was utilized as a carbon source. On the basis of the information described above, the name Ferroplasma acidiphilum gen. nov., sp. nov. is proposed for strain Y T within a new family, the Ferroplasmaceae fam. nov. Strain Y T is the type and only strain of F. acidiphilum. This is the first report of an autotrophic, ferrous-ironoxidizing, cell-wall-lacking archaeon.

Polyphasic genotypic analysis of 25 Acidithiobacillus ferrooxidans strains isolated from ores and ore concentrates collected in different regions of the world showed considerable strain heterogeneity. Restriction patterns of the chromosomal DNA of these strains obtained by PFGE were specific for each strain. According to the degree of DNA relatedness, 17 of the 23 strains studied were divided into four genomovars. Six independent, considerably divergent strains could not be assigned to any of the genomovars. A comparison of nearly complete nucleotide sequences of the 16S rDNA of five representatives of the genomovars (including the type strain of A. ferrooxidans, ATCC 23270 T ) with those of species of the genus Acidithiobacillus available from GenBank showed that most of the A. ferrooxidans strains, together with the type strain and some other strains of the species Acidithiobacillus thiooxidans, comprised a monophyletic cluster. Within this major cluster, A. ferrooxidans strains fell into four phylogenetic groups that were equidistant from the phylogenetic group of A. thiooxidans strains. In general, the distribution of strains among the phylogenetic groups correlated with their distribution among the genomovars, except that the representatives of two different genomovars fell into one phylogenetic group. Thus, at least two levels of phylogenetic heterogeneity for A. ferrooxidans have been found. The phylogenetic heterogeneity of A. ferrooxidans strains, which are phenotypically indistinguishable, suggests the occurrence of microevolutionary processes in different econiches. This should be taken into account in the biohydrometallurgical applications of A. ferrooxidans strains.

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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...

Microbial population performing biooxidation of flotation concentrate of gold bearing sulfide ore containing pyrite, arsenopyrite, and pyrrhotite was studied using cultural and molecular biological (metagenomics sequencing of V3-V4 fragments of 16S rRNA gene) approaches. The biooxidation of the concentrate was conducted at temperatures from 38 to 42°C. Strains of Acidithiobacillus thiooxidans, Acidiphilium multivorum, Leptospirillum ferriphilum, Sulfobacillus thermotolerans, Ferroplasma acidarmanus, and Ferroplasma acidiphilum were isolated from the samples of the pulp from biooxidation reactors. It was shown that optimum temperatures of isolated strains were from 38 to 40°C. Metagenomic analysis demonstrated predominance of the genera Acidiferrobacter, Acidithiobacillus, Acidiphilum, Leptospirillum, and Ferroplasma. According to results of molecular biological analysis, share of the genus Acidithiobacillus was of 0 to 25%, share of the genus Acidiferrobacter was of 7 to 56%, share of the genus Acidiphilum was of 0.03 to 36%, share of the genus Leptospirillum was of 0.7 to 7%, whereas share of the archaea of the genus Ferroplasma was of 33 to 94%. Thus, it was shown that representatives of the genus Ferroplasma can play significant role in bioleach process. Representatives of the genus Acidiferrobacter were previously detected in acid mine drainages, acid soils as well as in bioleach heaps and reactors, whereas data on predominance of the genus in tank bioleach processes have not been presented in the literature. In the present study, strains of the genus Acidiferrobacter were not isolated despite application of the nutrient media recommended for Acidiferrobacter and their properties were not studied. Nevertheless, results of the present study suggest that representatives of the genus Acidiferrobacter have a great impact on industrial bioleach processes.