Characterization of a novel thiosulfate dehydrogenase from a marine acidophilic sulfur-oxidizing bacterium,Acidithiobacillus thiooxidans strain SH

A marine acidophilic sulfur-oxidizing bacterium, Acidithiobacillus thiooxidans strain SH, was isolated to develop a bioleaching process for NaCl-containing sulfide minerals. Because the sulfur moiety of sulfide minerals is metabolized to sulfate via thiosulfate as an intermediate, we purified and characterized the thiosulfate dehydrogenase (TSD) from strain SH. The enzyme had an apparent molecular mass of 44 kDa and was purified 71-fold from the solubilized membrane fraction. Tetrathionate was the product of the TSD-oxidized thiosulfate and ferricyanide or ubiquinone was the electron acceptor. Maximum enzyme activity was observed at pH 4.0, 40 °C, and 200 mM NaCl. To our knowledge, this is the first report of NaCl-stimulated TSD activity. TSD was structurally different from the previously reported thiosulfate-oxidizing enzymes. In addition, TSD activity was strongly inhibited by 2-heptyl-4-hydroxy-quinoline N-oxide, suggesting that the TSD is a novel thiosulfate:quinone reductase.     

Roseinatronobacter thiooxidans Gen. Nov., sp. Nov., a new alkaliphilic aerobic bacteriochlorophyll-alpha-containing bacteria from a soda lake

Several samples of microbial mat obtained from soda lakes of the Kunkurskaya steppe (Chita oblast) abundantly populated by purple bacteria were screened for the presence of heterotrophic alkaliphiles capable of oxidizing sulfur compounds to sulfate. This capacity was found in only one pigmented strain, ALG 1, isolated on medium with acetate and thiosulfate at pH 10. The strain was found to be a strictly aerobic and obligately heterotrophic alkaliphile. Growth on medium with acetate was possible within a narrow pH range from 8.5 to 10.4. The strain formed a reddish orange carotenoid and bacteriochlorophyll a. Pigments were synthesized only at high concentrations of nitrogen-containing organic compounds (peptone or yeast extract). The production of bacteriochlorophyll a was maximal under microaerobic conditions in darkness. Strain ALG 1 could oxidize sulfide, thiosulfate, sulfite, and elemental sulfur to sulfate. In heterotrophically growing culture (pH 10), thiosulfate was not oxidized until the late logarithmic phase. The sulfur-oxidizing activity was maximal at the most alkaline pH values. The notable increase in the efficiency of organic carbon utilization observed in the presence of thiosulfate suggested that the bacterium was a sulfur-oxidizing lithoheterotroph. The phylogenetic analysis of the 16S rRNA gene showed strain ALG 1 to be a member of the alpha-3 subgroup of proteobacteria and to constitute a distinct branch located between nonsulfur purple bacteria Rhodobacter and Rhodovulum. Based on the unique phenotypic properties and the results of phylogenetic analysis, the alkaliphilic isolate ALG 1 was assigned to a new genus and species Roseinatronobacter thiooxidans with the type strain DSZM-13087.     

Isolation, characterization, and in situ detection of a novel chemolithoautotrophic sulfur-oxidizing bacterium in wastewater biofilms growing under microaerophilic conditions

We successfully isolated a novel aerobic chemolithotrophic sulfur-oxidizing bacterium, designated strain SO07, from wastewater biofilms growing under microaerophilic conditions. For isolation, the use of elemental sulfur (S(0)), which is the most abundant sulfur pool in the wastewater biofilms, as the electron donor was an effective measure to establish an enrichment culture of strain SO07 and further isolation. 16S rRNA gene sequence analysis revealed that newly isolated strain SO07 was affiliated with members of the genus Halothiobacillus, but it was only distantly related to previously isolated species (89% identity). Strain SO07 oxidized elemental sulfur, thiosulfate, and sulfide to sulfate under oxic conditions. Strain SO07 could not grow on nitrate. Organic carbons, including acetate, propionate, and formate, could not serve as carbon and energy sources. Unlike other aerobic sulfur-oxidizing bacteria, this bacterium was sensitive to NaCl; growth in medium containing more than 150 mM was negligible. In situ hybridization combined with confocal laser scanning microscopy revealed that a number of rod-shaped cells hybridized with a probe specific for strain SO07 were mainly present in the oxic biofilm strata (ca. 0 to 100 micro m) and that they often coexisted with sulfate-reducing bacteria in this zone. These results demonstrated that strain SO07 was one of the important sulfur-oxidizing populations involved in the sulfur cycle occurring in the wastewater biofilm and was primarily responsible for the oxidation of H(2)S and S(0) to SO(4)(2-) under oxic conditions.     

Roseinatronobacter thiooxidans gen. nov., sp. nov., a new alkaliphilic aerobic bacteriochlorophylla—containing bacterium isolated from a soda lake

Several samples of microbial mat obtained from soda lakes of the Kunkurskaya steppe (Chita region) abundantly populated by purple bacteria were screened for the presence of heterotrophic alkaliphiles capable of oxidizing sulfur compounds to sulfate. This capacity was found in only one pigmented strain, ALG 1, isolated on medium with acetate and thiosulfate at pH 10. The strain was found to be a strictly aerobic and obligately heterotrophic alkaliphile. Growth on medium with acetate was possible within a narrow pH range from 8.5 to 10.4. The strain formed a reddish orange carotenoid and bacteriochlorophylla. Pigments were synthesized only at high concentrations of nitrogen-containing organic compounds (peptone or yeast extract). The production of bacteriochlorophylla was maximal under microaerobic conditions in darkness. Strain ALG 1 could oxidize sulfide, thiosulfate, sulfite, and elemental sulfur to sulfate. In heterotrophically growing culture (pH 10), thiosulfate was not oxidized until the late logarithmic phase. The sulfur-oxidizing activity was maximal at the most alkaline pH values. The notable increase in the efficiency of organic carbon utilization observed in the presence of thiosulfate suggested that the bacterium was a sulfur-oxidizing lithoheterotroph. The phylogenetic analysis of the 16S rRNA gene showed strain ALG 1 to be a member of the α-3 subgroup of Proteobacteria and to constitute a distinct branch located between nonsulfur purple bacteriaRhodobacter andRhodovulum. Based on the unique phenotypic properties and the results of phylogenetic analysis, the alkaliphilic isolate ALG 1 was assigned to a new genus and speciesRoseinatronobacter thiooxidans with the type strain DSM-13087     

Isolation of an extremely acidophilic and highly efficient strain Acidithiobacillus sp. for chalcopyrite bioleaching

An extremely acidophilic sulfur-oxidizing bacterium was isolated from an industrial-scale bioheap of the Zijinshan copper mine and was named ZJJN. A tuft of flagella and a layer of thick capsule outside the cell envelope were clearly observed under transmission electron microscopy (TEM), which might be closely related to the extremely acid-proof capacity of ZJJN cells in the bioleaching system; 16S ribosomal RNA (rRNA) phylogeny showed that the isolated strain was highly homologous to the genera of Acidithiobacillus. The optimum temperature of ZJJN was determined at 30?°C and pH at 1.0. It was capable of growth at even pH 0. Strain ZJJN can utilize reduced sulfur as an energy source but not with organics or ferrous ion. Strain ZJJN was sensitive to all antibiotics with different concentrations; when it showed a certain resistance to different concentrations of Cu²⁺. In the mixed strains of ZJJN and A. ferrooxidans system (initial pH 1.0), the copper-leaching efficiency was up to 60.1?%, which was far higher than other systems. Scanning electron microscopy (SEM) analysis showed that less jarosite precipitation was produced in the most efficient system. The extremely acidophilic strain ZJJN would be of great potential in the application of chalcopyrite bioleaching.     

Effects of inhibitors and NaCl on the oxidation of reduced inorganic sulfur compounds by a marine acidophilic, sulfur-oxidizing bacterium, Acidithiobacillus thiooxidans strain SH

The effect of NaCl and the pathways of the oxidation of reduced inorganic sulfur compounds were studied using resting cells and cell-free extracts of Acidithiobacillus thiooxidans strain SH. This isolate specifically requires NaCl for growth. The oxidation of sulfur and sulfite by resting cells was strongly inhibited by 2-heptyl-4-hydroxyquinoline-N-oxide. Carbonylcyanide m-chlorophenyl-hydrazone and monensin were also relatively strong inhibitors. Thiosulfate-oxidizing activity was not inhibited by these uncouplers. Valinomycin did not inhibit the oxidation of sulfur compounds. NaCl stimulated the sulfur- and sulfite-oxidizing activities in resting cells but not in cell-free extracts. The tetrathionate-oxidizing activity in resting cells was slightly stimulated by NaCl, whereas it did not influence the thiosulfate-oxidizing activity. Sulfide oxidation was biphasic, suggesting the formation of intermediate sulfur. The initial phase of sulfide oxidation was not affected by NaCl, whereas the subsequent oxidation of sulfur in the second phase was Na⁺-dependent. A model is proposed for the role of NaCl in the metabolism of reduced sulfur compounds in A. thiooxidans strain SH.     

Isolation, Characterization, and In Situ Detection of a Novel Chemolithoautotrophic Sulfur-Oxidizing Bacterium in Wastewater Biofilms Growing under Microaerophilic Conditions

We successfully isolated a novel aerobic chemolithotrophic sulfur-oxidizing bacterium, designated strain SO07, from wastewater biofilms growing under microaerophilic conditions. For isolation, the use of elemental sulfur (S⁰), which is the most abundant sulfur pool in the wastewater biofilms, as the electron donor was an effective measure to establish an enrichment culture of strain SO07 and further isolation. 16S rRNA gene sequence analysis revealed that newly isolated strain SO07 was affiliated with members of the genus Halothiobacillus, but it was only distantly related to previously isolated species (89% identity). Strain SO07 oxidized elemental sulfur, thiosulfate, and sulfide to sulfate under oxic conditions. Strain SO07 could not grow on nitrate. Organic carbons, including acetate, propionate, and formate, could not serve as carbon and energy sources. Unlike other aerobic sulfur-oxidizing bacteria, this bacterium was sensitive to NaCl; growth in medium containing more than 150 mM was negligible. In situ hybridization combined with confocal laser scanning microscopy revealed that a number of rod-shaped cells hybridized with a probe specific for strain SO07 were mainly present in the oxic biofilm strata (ca. 0 to 100 μm) and that they often coexisted with sulfate-reducing bacteria in this zone. These results demonstrated that strain SO07 was one of the important sulfur-oxidizing populations involved in the sulfur cycle occurring in the wastewater biofilm and was primarily responsible for the oxidation of H₂S and S⁰ to SO₄²⁻ under oxic conditions.     

Characterization of tetrathionate hydrolase from the marine acidophilic sulfur-oxidizing bacterium,Acidithiobacillus thiooxidans strain SH

Tetrathionate hydrolase (4THase), a key enzyme of the S₄-intermediate (S4I) pathway, was partially purified from marine acidophilic bacterium, Acidithiobacillus thiooxidans strain SH, and the gene encoding this enzyme (SH-tth) was identified. SH-Tth is a homodimer with a molecular mass of 97 ± 3 kDa, and contains a subunit 52 kDa in size. Enzyme activity was stimulated in the presence of 1 M NaCl, and showed the maximum at pH 3.0. Although 4THases from A. thiooxidans and the closely related Acidithiobacillus caldus strain have been reported to be periplasmic enzymes, SH-Tth seems to be localized on the outer membrane of the cell, and acts as a peripheral protein. Furthermore, both 4THase activity and SH-Tth proteins were detected in sulfur-grown cells of strain SH. These results suggested that SH-Tth is involved in elemental sulfur-oxidation, which is distinct from sulfur-oxidation in other sulfur-oxidizing strains such as A. thiooxidans and A. caldus.     

Isolation and characterization of a sulfur-oxidizing chemolithotroph growing on crude oil under anaerobic conditions

Molecular approaches have shown that a group of bacteria (called cluster 1 bacteria) affiliated with the epsilon subclass of the class Proteobacteria constituted major populations in underground crude-oil storage cavities. In order to unveil their physiology and ecological niche, this study isolated bacterial strains (exemplified by strain YK-1) affiliated with the cluster 1 bacteria from an oil storage cavity at Kuji in Iwate, Japan. 16S rRNA gene sequence analysis indicated that its closest relative was Thiomicrospira denitrificans (90% identity). Growth experiments under anaerobic conditions showed that strain YK-1 was a sulfur-oxidizing obligate chemolithotroph utilizing sulfide, elemental sulfur, thiosulfate, and hydrogen as electron donors and nitrate as an electron acceptor. Oxygen also supported its growth only under microaerobic conditions. Strain YK-1 could not grow on nitrite, and nitrite was the final product of nitrate reduction. Neither sugars, organic acids (including acetate), nor hydrocarbons could serve as carbon and energy sources. A typical stoichiometry of its energy metabolism followed an equation: S(2-) + 4NO(3)(-) --> SO(4)(2-) + 4NO(2)(-) (Delta G(0) = -534 kJ mol(-1)). In a difference from other anaerobic sulfur-oxidizing bacteria, this bacterium was sensitive to NaCl; growth in medium containing more than 1% NaCl was negligible. When YK-1 was grown anaerobically in a sulfur-depleted inorganic medium overlaid with crude oil, sulfate was produced, corresponding to its growth. On the contrary, YK-1 could not utilize crude oil as a carbon source. These results suggest that the cluster 1 bacteria yielded energy for growth in oil storage cavities by oxidizing petroleum sulfur compounds. Based on its physiology, ecological interactions with other members of the groundwater community are discussed.     

Denitrification at extremely high pH values by the alkaliphilic, obligately chemolithoautotrophic, sulfur-oxidizing bacterium Thioalkalivibrio denitrificans strain ALJD

Thioalkalivibrio denitrificans is the first example of an alkaliphilic, obligately autotrophic, sulfur-oxidizing bacterium able to grow anaerobically by denitrification. It was isolated from a Kenyan soda lake with thiosulfate as electron donor and N2O as electron acceptor at pH 10. The bacterium can use nitrite and N2O, but not nitrate, as electron acceptors during anaerobic growth on reduced sulfur compounds. Nitrate is only utilized as nitrogen source. In batch culture at pH 10, rapid growth was observed on N2O as electron acceptor and thiosulfate as electron donor. Growth on nitrite was only possible after prolonged adaptation of the culture to increasing nitrite concentrations. In aerobic thiosulfate-limited chemostats, Thioalkalivibrio denitrificans strain ALJD was able to grow between pH values of 7.5 and 10.5 with an optimum at pH 9.0. Growth of the organism in continuous culture on N2O was more stable and faster than in aerobic cultures. The pH limit for growth on N2O was 10.6. In nitrite-limited chemostat culture, growth was possible on thiosulfate at pH 10. Despite the observed inhibition of N2O reduction by sulfide, the bacterium was able to grow in sulfide-limited continuous culture with N2O as electron acceptor at pH 10. The highest anaerobic growth rate with N2O in continuous culture at pH 10 was observed with polysulfide (S8(2-)) as electron donor. Polysulfide was also the best substrate for oxygen-respiring cells. Washed cells at pH 10 oxidized polysulfide to sulfate via elemental sulfur in the presence of N2O or O2. In the absence of the electron acceptors, elemental sulfur was slowly reduced which resulted in regeneration of polysulfide. Cells of strain ALJD grown under anoxic conditions contained a soluble cd1-like cytochrome and a cytochrome-aa3-like component in the membranes.     

Desulfotomaculum geothermicum sp. nov., a thermophilic,fatty acid-degrading,sulfate-reducing bacterium isolated with H2 from geothermal ground water

A strictly anaerobic, thermophilic, fatty acids-degrading, sporulating sulfate-reducing bacterium was isolated from geothermal ground water. The organism stained Gram-negative and formed gas vacuoles during sporulation. Lactate, ethanol, fructose and saturated fatty acids up to C₁₈ served as electron donors and carbon sources with sulfate as external electron acceptor. Benzoate was not used. Stoichiometric measurements revealed a complete oxidation of part of butyrate although growth with acetate as only electron donor was not observed. The rest of butyrate was oxidized to acetate. The strain grew chemolithoautotrophically with hydrogen plus sulfate as energy source and carbon dioxide as carbon source without requirement of additional organic carbon like acetate. The strain contained a c-type cytochrome and presumably a sulfite reductase P582. Optimum temperature, pH and NaCl concentration for growth were 54°C, pH 7.3–7.5 and 25 to 35 g NaCl/l. The G+C content of DNA was 50.4 mol %. Strain BSD is proposed as a new species of the spore-forming sulfate-reducing genus Desulfotomaculum, D. geothermicum.     

Nickel Inhibition of the Growth of a Sulfur-oxidizing Bacterium Isolated from Corroded Concrete

A sulfur-oxidizing bacterium strain NB1-3 isolated from corroded concrete was a Gram negative, non-spore-forming, and rod-shaped bacterium (0.5–1.0x 1.5–2.0μm) with a polar flagellum. Strain NB1-3 had its optimum temperature and pH for growth at 30°C and 3.0–4.0, respectively. Strain NB1-3 had enzyme activities that oxidized elemental sulfur, thiosulfate, tetrathionate, and sulfide and the activity to incorporate ¹⁴CO₂ into the cells. The mean G+C content of the DNA was 52.9 mol%. These results indicate that strain NB1-3 is Thiobacillus thiooxidans. Since nickel has been known to protect concrete from corrosion, the effect of Ni on the growth of strain NB1-3 was studied. The cell growth on tiosulfate-, elemental sulfur-, or tetrathionate-medium was completely inhibited by 0.1% metal nickel or 5mM NiSO₄. Both cellular activities of elemental sulfur oxidation and CO₂ incorporation were strongly inhibited by 5mM NiSO₄. The amounts of Ni in cells with or without nickel treatment were 1.7 and 160.0 nmol/mg protein, respectively. These results indicate that nickel binds to strain NB1-3 cells and inhibits enzymes involved in sulfur oxidation of this bacterium, and as a result, inhibits cell growth.     

一株嗜酸硫氧化菌的分离

从江西德兴分离得到一株嗜酸硫氧化杆菌DX-2,采用双层固体培养基进行分离纯化,对分离菌株进行了形态、生理生化特性研究及16SrRNA序列分析.该菌株为革兰氏阴性细菌,短杆状,菌体大小（0.4～0.5）μm×（1～2）μm,化能自养,可利用硫磺和硫代硫酸盐为能源生长,不能利用亚铁进行生长.以16SrRNA序列同源性为基础构建了相关种属在内的系统发育树,结果表明,DX-2与喜温硫杆菌（Acidithiobacillus caldus）处于同一进化树分支中,相似性达99%以上.考察了不同重金属离子对DX-2的生长的影响.     

Effect of Salts on Growth and Pectinase Production by Halotolerant Yeast, <Emphasis Type="Italic">Debaryomyces nepalensis</Emphasis> NCYC 3413

In this study, Debaryomyces nepalensis NCYC 3413 isolated from rotten apple was studied for its halotolerance and its growth was compared with that of Saccharomyces cerevisiae in high salt medium. The specific growth rate of D. nepalensis was not affected by KCl even up to a concentration of 1 M, whereas NaCl and LiCl affected the growth of D. nepalensis. Among all tested salts, LiCl showed maximum inhibition on growth. At all conditions, halotolerance of D. nepalensis was much higher than that of S. cerevisiae. D. nepalensis showed maximum viability (80–100%) when grown in KCl, which was higher than with NaCl and LiCl. Pectinase production by D. nepalensis was noted at all high salt concentrations, namely, 2 M NaCl, 2 M KCl, and 0.5 M LiCl, and the maximum specific activity was observed when the strain was grown in 2 M NaCl.     

A hydrocarbon-oxidizing acidophilic thermotolerant bacterial association from sulfur blocks

A stable bacterial association isolated from a sulfur block sample of the Astrakhan gas processing complex was able to utilize n-alkanes as the sole carbon and energy source at low pH. Hydrocarbon-dependent growth occurred at pH 1.6–5.5 (optimum at pH 2.5) and 20–50°C (optimum at 30–35°C). Analysis of the 16S rRNA gene fragments isolated from the total DNA of the enrichment by PCR-DGGE revealed the nucleotide sequences most closely related to extreme acidophilic chemolithotrophs Acidithiobacillus thiooxidans and Sulfobacillus sp. (98–99% similarity) and the sequences exhibiting high similarity to those of slowly growing actinobacteria Mycobacterium europaeum and M. parascrofulaceum (98%). Capacity of any of these organisms for hydrocarbon oxidation has not been reported previously. The taxonomic position of the 16S rRNA gene fragments from the enrichment culture suggests that this bacterial association is a unique microbial community, in which development of acidophilic hydrocarbon-oxidizing bacteria is mediated by a localized pH decrease in the sulfur blocks resulting from elemental sulfur oxidation due to massive development of chemolithotrophic sulfur-oxidizing bacteria.     

Effect of cultivation conditions on the growth and activities of sulfur metabolism enzymes and carboxylases of Sulfobacillus thermosulfidooxidans subsp. asporogenes strain 41

The moderately thermophilic acidophilic bacterium Sulfobacillus thermosulfidooxidans subsp. asporogenes strain 41 is capable of utilizing sulfides of gold-arsenic concentrate and elemental sulfur as a source of energy. The growth in the presence of S0 under auto- or mixotrophic conditions was less stable compared with the media containing iron monoxide. The enzymes involved in oxidation of sulfur inorganic compounds--thiosulfate-oxidizing enzyme, tetrathionate hydrolase, rhodonase, adenylyl sulfate reductase, sulfite oxidase, and sulfur oxygenase--were discovered in the cells of Sulfobacillus grown in the mineral medium containing 0.02% yeast extract and either sulfur or iron monoxide and thiosulfate. Cell-free extracts of the cultures grown in the medium with sulfur under auto- or mixotrophic conditions displayed activity of the key enzyme of the Calvin cycle--ribulose bisphosphate carboxylase--and several other enzymes involved in heterotrophic fixation of carbonic acid. Activities of carboxylases depended on the composition of cultivation media.     

嗜酸硫氧化细菌消解元素硫的研究进展

浸矿酸性环境下,金属硫化矿在Fe3+作用下,经过硫代硫酸盐途径或多聚硫化氢途径而分解的过程中导致大量元素硫的累积,进而可能在金属硫化矿表面形成疏水元素硫层,阻碍金属离子的进一步浸出。酸性环境下,惰性元素硫的消解必须借助嗜酸硫氧化细菌来实现。该消解过程包括嗜酸硫氧化细菌对元素硫的吸附、转运以及氧化转化等过程。本文对近年来嗜酸硫氧化细菌消解元素硫过程的相关研究进行了全面评述,认为有关嗜酸硫氧化细菌消解元素硫的分子机制的清晰阐述还有待人们通过对消解过程的各个环节的分子机制进行大量研究来实现。     

Acidophilic haloarchaeal strains are isolated from various solar salts

Haloarchaeal strains require high concentrations of NaCl for their growth, with optimum concentrations of 10–30%. They display a wide variety of morphology and physiology including pH range for growth. Many strains grow at neutral to slightly alkaline pH, and some only at alkaline pH. However, no strain has been reported to grow only in acidic pH conditions within the family Halobacteriaceae. In this study, we isolated many halophiles capable of growth in a 20% NaCl medium adjusted to pH 4.5 from 28 commercially available salts. They showed growth at pH 4.0 to 6.5, depending slightly on the magnesium content. The most acidophilic strain MH1-52-1 isolated from an imported solar salt (pH of saturated solution was 9.0) was non-pigmented and extremely halophilic. It was only capable of growing at pH 4.2–4.8 with an optimum at pH 4.4 in a medium with 0.1% magnesium chloride, and at pH 4.0–6.0 (optimum at pH 4.0) in a medium with 5.0% magnesium. The 16S rRNA and DNA-dependent RNA polymerase subunit B' gene sequences demonstrated clearly that the strain MH1-52-1 represents a new genus in the family Halobacteriaceae.     

Isolation of a strain of <Emphasis Type="Italic">Acidithiobacillus caldus</Emphasis> and its role in bioleaching of chalcopyrite

A moderately thermophilic and acidophilic sulfur-oxidizing bacterium named S₂, was isolated from coal heap drainage. The bacterium was motile, Gram-negative, rod-shaped, measured 0.4 to 0.6 by 1 to 2 μm, and grew optimally at 42–45°C and an initial pH of 2.5. The strain S₂ grew autotrophically by using elemental sulfur, sodium thiosulfate and potassium tetrathionate as energy sources. The strain did not use organic matter and inorganic minerals including ferrous sulfate, pyrite and chalcopyrite as energy sources. The morphological, biochemical, physiological characterization and analysis based on 16S rRNA gene sequence indicated that the strain S₂ is most closely related to Acidithiobacillus caldus (>99% similarity in gene sequence). The combination of the strain S₂ with Leptospirillum ferriphilum or Acidithiobacillus ferrooxidans in chalcopyrite bioleaching improved the copper-leaching efficiency. Scanning electron microscope (SEM) analysis revealed that the chalcopyrite surface in a mixed culture of Leptospirillum ferriphilum and Acidithiobacillus caldus was heavily etched. The energy dispersive X-ray (EDX) analysis indicated that Acidithiobacillus caldus has the potential role to enhance the recovery of copper from chalcopyrite by oxidizing the sulfur formed during the bioleaching progress.     

<Emphasis Type="Italic">Thialkalivibrio halophilus</Emphasis> sp. nov., a novel obligately chemolithoautotrophic,facultatively alkaliphilic,and extremely salt-tolerant,sulfur-oxidizing bacterium from a hypersaline alkaline lake

A new chemolithoautotrophic, facultatively alkaliphilic, extremely salt-tolerant, sulfur-oxidizing bacterium was isolated from an alkaline hypersaline lake in the Altai Steppe (Siberia, Russia). According to 16S rDNA analysis and DNA–DNA hybridization, strain HL 17^T was identified as a new species of the genus Thialkalivibrio belonging to the subdivision of the Proteobacteria for which the name Thialkalivibrio halophilus is proposed. Strain HL 17^T is an extremely salt-tolerant bacterium growing at sodium concentrations between 0.2 and 5 M, with an optimum of 2 M Na⁺. It grew at high concentrations of NaCl and of Na₂CO₃/NaHCO₃ (soda). Strain HL 17^T is a facultative alkaliphile growing at pH range 7.5–9.8, with a broad optimum between pH 8.0 and 9.0. It used reduced inorganic sulfur compounds (thiosulfate, sulfide, polysulfide, elemental sulfur, and tetrathionate) as energy sources and electron donors. In continuous culture under energy limitation, thiosulfate was stoichiometrically oxidized to sulfate. In sodium carbonate medium under alkaline conditions, the maximum growth rate was similar, while the biomass yield was lower as compared with the NaCl-grown culture. The maximum sulfur-oxidizing capacity measured in washed cells was higher in the soda buffer independent of the growth conditions. The compatible solute content of the biomass was higher in the sodium chloride-grown culture than in the sodium carbonate/bicarbonate-grown culture. The data suggest that the osmotic pressure differences between soda and NaCl solutions might be responsible for the difference observed in compatible solutes production. This may have important implications in overall energetic metabolism of high salt adaptation.