Paul R. Norris

Acidimicrobium ferrooxidans gen. nov., sp. nov. : mixed-culture ferrous iron oxidation with Sulfobacillus species

A new species of ferrous-iron-oxidizing, moderately thermophilic, acidophilic bacteria, Acidimicrobium ferrooxidans, has been described. Two isolates of the species differed only in the tendency of one, previously known as strain TH3, to grow in filaments. The chromosomal DNA base composition is between 67 and 69 mol% G + C. The capacity of this species to fix CO2 from air was greater than that of iron-oxidizing thermoacidophiles of the genus Sulfobacillus, which required an enhanced CO2 concentration for optimum autotrophic growth. Under air, ferrous iron oxidation in mixed cultures of A. ferrooxidans with either Sulfobacillus thermosulfidooxidans or Sulfobacillus acidophilus was more extensive than in pure cultures of these three strains. The greater part of ferrous iron oxidation in mixed cultures probably resulted from activity of the Sulfobacillus species, which possess a greater tolerance of ferric iron, and which presumably grew mixotrophically utilizing organic compounds from A. ferrooxidans.

Characteristics of Sulfobacillus acidophilus sp. nov. and other moderately thermophilic mineral-sulphide-oxidizing bacteria

Several isolates of Gram-positive, acidophilic, moderately thermophilic, ferrous-iron- and mineral-sulphide-oxidizing bacteria were examined to establish unequivocally the characteristics of Sulfobacillus-like bacteria. Two species were evident: Sulfobacillus thermosulfidooxidans with 48-50 mol% G+C and Sulfobacillus acidophilus sp. nov. with 55-57 mol% G+C. Both species grew autotrophically and mixotrophically on ferrous iron, on elemental sulphur in the presence of yeast extract, and heterotrophically on yeast extract. Autotrophic growth on sulphur was consistently obtained only with S. acidophilus.

Acidophiles in bioreactor mineral processing.

Abstract Mineral processing in bioreactors has become established in several countries during the past decade with industrial application of iron- and sulfur-oxidizing bacteria to release occluded gold from mineral sulfides. Cobalt extraction in bioreactors has also been commercialized, and development of high-temperature biooxidation of copper sulfides has reached pilot-plant scale. A variety of potentially useful mineral sulfide-oxidizing thermophiles have been recognized, but the most active strains have not been fully characterized.

Microbiology of acidic, geothermal springs of Montserrat: environmental rDNA analysis.

Abstract DNA was extracted from water and sediment samples taken from acidic, geothermal pools on the Caribbean island of Montserrat. 16S rRNA genes were amplified by PCR, cloned, sequenced, and examined to indicate some of the organisms that might be significant components of the in situ microbiota. A clone bank representing the lowest temperature pool that was sampled (33°C) was dominated by genes corresponding to two types of acidophiles: Acidiphilium-like mesophilic heterotrophs and thermotolerant Acidithiobacillus caldus. Three clone types with origins in low- and moderate- (48°C) temperature pools corresponded to bacteria that could be involved in metabolism of sulfur compounds: the aerobic A. caldus and putative anaerobic, moderately thermophilic, sulfur-reducing bacteria (from an undescribed genus and from the Desulfurella group). A higher-temperature sample indicated the presence of a Ferroplasma-like organism, dis-tinct from the other strains of these recently recognized acidophilic, iron-oxidizing members of the Euryarchaeota. Acidophilic Archaea from undescribed genera related to Sulfolobus and Acidianus were predicted to dominate the indigenous acidophilic archaeal population at the highest temperatures.

Ferrous Iron- and Sulfur-Induced Genes in Sulfolobus metallicus

ABSTRACT Genes of Sulfolobus metallicus that appeared to be upregulated in relation to growth on either ferrous iron or sulfur were identified using subtractive hybridization of cDNAs. The genes upregulated during growth on ferrous iron were found in a cluster, and most were predicted to encode membrane proteins. Quantitative reverse transcription-PCR of cDNA showed upregulation of most of these genes during growth on ferrous iron and pyrite compared to results during growth on sulfur. The highest expression levels observed included those for genes encoding proteins with similarities to cytochrome c oxidase subunits and a CbsA-like cytochrome. The genes identified here that may be involved in oxidation of ferrous iron by S. metallicus are termed fox genes. Of three available genomes of Sulfolobus species (S. tokodaii, S. acidocaldarius, and S. solfataricus), only that of S. tokodaii has a cluster of highly similar open reading frames, and only S. tokodaii of these three species was also able to oxidize ferrous iron. A gene encoding sulfur oxygenase-reductase was identified as the source of the dominant transcript in sulfur-grown cells of S. metallicus, with the predicted protein showing high identities to the previously described examples from S. tokodaii and species of Acidianus.

Oxidation of mineral sulphides by thermophilic microorganisms

Abstract Pyrite and arsenopyrite concentrates were oxidized during growth of a variety of acidophilic microorganisms over a wide temperature range. A mesophilic culture, comprising Thiobacillus ferrooxidans and Leptospirillum ferrooxidans as the principal iron-oxidizing bacteria, was used at 30C; Sulfobacillus thermosulfidooxidans was active in pure and mixed cultures at 48°C; and Sulfolobus-like, thermoacidophilic archaea were grown at up to 84°C At low mineral concentrations, the rate of pyrite/arsenopyrite dissolution was proportional to temperature. However, the use of elevated temperatures to increase rates of mineral processing over those obtainable with mesophiles appeared to be most practicable with moderately thermophilic bacteria because growth of Sulfolobus strain BC was inhibited at higher mineral concentrations. Two aspects of higher temperature bioleaching were emphasized: the unique capacity of Sulfolobus-like archaea forextensive chalcopyrite oxidation; and the requirement for progress in leaching at high mineral concentrations before the potential of these organisms can be realised in process development.

Characteristics of a moderately thermophilic and acidophilic iron-oxidizing Thiobacillus

SummaryThiobacillus TH1 is an acidophilic chemolithotrophic heterotroph growing at temperatures up to about 50°C on media containing ferrous iron or pyrite when supplemented with yeast extract or glutathione. Virtually no carbon dioxide fixation occurred during growth on iron with yeast extract. Its DNA contains 48 mol % guanine + cytosine. The organism effects the thermophilic leaching of metals from pyrite, chalcopyrite, CuS, and copper concentrates. Oxidation of soluble ferrous iron at pH 1.6 was competitively inhibited by ferric iron and had a Km of 7.3 mM FeSO4.

Acidophiles of saline water at thermal vents of Vulcano, Italy

Abstract. DNA was extracted from samples taken from close to acidic hydrothermal vents on shore of the Aeolian Island of Vulcano (Italy). RNA gene sequences were amplified by PCR, cloned, and sequenced. A sequence with an origin in samples at 35° and 45°C corresponded to that of a novel Acidithiobacillus species that was isolated from water close to the vents. Novel, iron-oxidizing mesophilic acidophiles were isolated through enrichment cultures with ferrous iron but were not represented in the clone banks of environmental rDNA. These acidophiles were related to Thiobacillus prosperus, which was isolated previously from Vulcano. The archaeal sequences that comprised a clone bank representing a high-temperature sample (75°C) corresponded to those of Acidianus brierleyi and of thermophiles previously isolated from Vulcano, Thermoplasma volcanium and Acidianus infernus.

A microbiological survey of Montserrat Island hydrothermal biotopes

Abstract In March 1996, a survey of hydrothermal sites on the island of Montserrat was carried out. Six sites (Galways Soufrière, Gages Upper and Lower Soufrières, Hot Water Pond, Hot River, and Tar River Soufrière) were mapped and sampled for chemical, ATP, and microbial analyses. The hydrothermal Soufrière sites on the slopes of the active Chances Peak volcano exhibited temperatures up to almost 100°C and were generally either mildly acidic at pH 5–7 or strongly acidic at pH 1.5–3, but with some hot streams and pools of low redox potential at pH 7–8. Hot Water Pond sites, comprising a series of heated pools near the western shoreline of the island, were neutral and saline, consistent with subsurface heating of entrained seawater. Biological activity shown by ATP analyses was greatest in near-neutral pH samples and generally decreased as acidity increased. A variety of heterotrophic and chemolithotrophic thermophilic organisms were isolated or observed in enrichment cultures. Most of the bacteria that were obtained in pure culture were familiar acidophiles and neutrophiles, but novel, iron-oxidizing species of Sulfobacillus were revealed. These species included the first mesophilic iron-oxidizing Sulfobacillus strains to be isolated and a strain with a higher maximum growth temperature (65°C) than the previously described moderately thermophilic Sulfobacillus species.

The potential for diazotrophy in iron-and sulfur-oxidizing acidophilic bacteria

Acetylene reduction was observed with ferrousiron-oxidizingThiobacillus ferrooxidans, as expected from previous studies with this bacterium. Acetylene reduction was also found during the growth ofT. ferrooxidans on tetrathionate. OnlyLeptospirillum ferrooxidans, one of several other phylogenetically diverse, ferrous-iron-and/or sulfur-oxidizing acidophilic microorganisms, also reduced acetylene. A reduction of the oxygen concentration in the culture atmosphere was necessary to alleviate inhibition of nitrogenase activity. DNA sequences homologous tonif structural genes were found in both organisms. Diazotrophic growth ofL. ferrooxidans was inferred from an increase in iron oxidation in ammonium-free medium when the oxygen concentration was limited and from apparent inhibition by acetylene under these conditions.