Arsenic toxicity is not due to a direct effect on the oxidation of reduced inorganic sulfur compounds byThiobacillus caldus

Response of growth and superoxide dismutase to enhanced arsenic in two Bacillus species

Species differences in inorganic arsenic tolerance were investigated by comparing the responses of Bacillus subtilis (B. subtilis) and Bacillus thuringiensis (B. thuringiensis) to elevated concentrations of As(III) and As(V). The cell densities in treatments were always lower during the experiment compared to controls, with the exception of exposure to 1.0 mg As(V) l(-1) on the first day. It was also found that relative growth rate (RGR) of B. thuringiensis was lower than that of B. subtilis. Furthermore, RGR of each Bacillus species was negative correlation with toxicity of inorganic arsenic. However, total cell number still increased in each treatment according to cell density and RGR assays. Superoxide dismutase (SOD) activity of both Bacillus species was promoted by As(III) and As(V), especially under high arsenic concentration condition. In addition, SOD activity of B. thuringiensis was higher than that of B. subtilis during the same exposure time. In lipid peroxidation assay, thiobarbituric acid-reactive substances (TBARS) content of each Bacillus species had a significant increase with increment of arsenic concentration. Moreover, significant difference was observed between the two Bacillus species under high arsenic concentration. TBARS content of B. thuringiensis was higher than that of B. subtilis, indicating that effect of arsenic on cell membranes of B. thuringiensis was much more than that of B. subtilis. These results suggest that the two Bacillus species could adapt and live in high arsenic aquifers, although their growth and cell membranes were affected by As treatment in a way.

Metal resistance in acidophilic microorganisms and its significance for biotechnologies

Extremely acidophilic microorganisms have an optimal pH of <3 and are found in all three domains of life. As metals are more soluble at acid pH, acidophiles are often challenged by very high metal concentrations. Acidophiles are metal-tolerant by both intrinsic, passive mechanisms as well as active systems. Passive mechanisms include an internal positive membrane potential that creates a chemiosmotic gradient against which metal cations must move, as well as the formation of metal sulfate complexes reducing the concentration of the free metal ion. Active systems include efflux proteins that pump metals out of the cytoplasm and conversion of the metal to a less toxic form. Acidophiles are exploited in a number of biotechnologies including biomining for sulfide mineral dissolution, biosulfidogenesis to produce sulfide that can selectively precipitate metals from process streams, treatment of acid mine drainage, and bioremediation of acidic metal-contaminated milieux. This review describes how acidophilic microorganisms tolerate extremely high metal concentrations in biotechnological processes and identifies areas of future work that hold promise for improving the efficiency of these applications.

Comparative genome analysis reveals metabolic versatility and environmental adaptations of Sulfobacillus thermosulfidooxidans strain ST

The genus Sulfobacillus is a cohort of mildly thermophilic or thermotolerant acidophiles within the phylum Firmicutes and requires extremely acidic environments and hypersalinity for optimal growth. However, our understanding of them is still preliminary partly because few genome sequences are available. Here, the draft genome of Sulfobacillus thermosulfidooxidans strain ST was deciphered to obtain a comprehensive insight into the genetic content and to understand the cellular mechanisms necessary for its survival. Furthermore, the expressions of key genes related with iron and sulfur oxidation were verified by semi-quantitative RT-PCR analysis. The draft genome sequence of Sulfobacillus thermosulfidooxidans strain ST, which encodes 3225 predicted coding genes on a total length of 3,333,554 bp and a 48.35% G+C, revealed the high degree of heterogeneity with other Sulfobacillus species. The presence of numerous transposases, genomic islands and complete CRISPR/Cas defence systems testifies to its dynamic evolution consistent with the genome heterogeneity. As expected, S. thermosulfidooxidans encodes a suit of conserved enzymes required for the oxidation of inorganic sulfur compounds (ISCs). The model of sulfur oxidation in S. thermosulfidooxidans was proposed, which showed some different characteristics from the sulfur oxidation of Gram-negative A. ferrooxidans. Sulfur oxygenase reductase and heterodisulfide reductase were suggested to play important roles in the sulfur oxidation. Although the iron oxidation ability was observed, some key proteins cannot be identified in S. thermosulfidooxidans. Unexpectedly, a predicted sulfocyanin is proposed to transfer electrons in the iron oxidation. Furthermore, its carbon metabolism is rather flexible, can perform the transformation of pentose through the oxidative and non-oxidative pentose phosphate pathways and has the ability to take up small organic compounds. It encodes a multitude of heavy metal resistance systems to adapt the heavy metal-containing environments.

Construction of recombinant mercury resistant Acidithiobacillus caldus

A mercury-resistant plasmid of pTMJ212 which was able to shuttle between Acidithiobacillus caldus and Escherichia coli was constructed by inserting the mercury resistant determinants, the mer operon of Acidithiobacillus ferrooxidans, into the IncQ plasmid of pJRD215. pTMJ212 was transferred from Escherichia coli into Acidithiobacillus caldus through conjugation. Furthermore, pTMJ212 was transferred back from Acidithiobacillus caldus into Escherichia coli, thereby confirming the initial transfer of pTMJ212 from Escherichia coli to Acidithiobacillus caldus. Compared to the control, the cell growth of the recombinant Acidithiobacillus caldus increased markedly under mercury (Hg(2+)) stress especially at Hg(2+) concentrations ranging from 2.0 to 4.5 μg/ml.

The resilience and versatility of acidophiles that contribute to the bio-assisted extraction of metals from mineral sulphides

In this paper, a brief outline is presented on acidic ferric ion oxidation of mineral sulphides for the extraction of metals in both stirred tank reactors for mineral concentrates and heaps for low-grade ores. The identities and capabilities of the relatively few acidophiles that assist the oxidative processes are summarized and their responses to selected extremes in their growth environments described. Individually, the organisms adapt to the presence of high concentrations of heavy metals and other elements in the bioleaching environment, tolerate a wide range of acidities and can recover from prolonged exposure to temperatures significantly above their preferred temperatures for growth. However, the presence of chloride in their acidic environment presents a significant physiological challenge. Species that exhibit a chemotactic response and attachment to sulphide surfaces, where they can create their own micro-environments, would be favoured in both heap bioreactors with low availability of energy substrates and physically aggressive, agitated continuous stirred-tank reactor environments treating concentrates.

Kinetic constant variability in bacterial oxidation of elemental sulfur

Wide ranges of growth yields on sulfur (from 2.4 x 10(10) to 8.1 x 10(11) cells g(-1)) and maximum sulfur oxidation rates (from 0.068 to 1.30 mmol liter(-1) h(-1)) of an Acidithiobacillus ferrooxidans strain (CCM 4253) were observed in 73 batch cultures. No significant correlation between the constants was observed. Changes of the Michaelis constant for sulfur (from 0.46 to 15.5 mM) in resting cells were also noted.

Molecular insight into extreme copper resistance in the extremophilic archaeon 'Ferroplasma acidarmanus' Fer1

'Ferroplasma acidarmanus' strain Fer1 is an extremely acidophilic archaeon involved in the genesis of acid mine drainage, and was isolated from copper-contaminated mine solutions at Iron Mountain, CA, USA. Here, the initial proteomic and molecular investigation of Cu(2+) resistance in this archaeon is presented. Analysis of Cu(2+) toxicity via batch growth experiments and inhibition of oxygen uptake in the presence of ferrous iron demonstrated that Fer1 can grow and respire in the presence of 20 g Cu(2+) l(-1). The Fer1 copper resistance (cop) loci [originally detected by Ettema, T. J. G., Huynen, M. A., de Vos, W. M. & van der Oost, J. Trends Biochem Sci 28, 170-173 (2003)] include genes encoding a putative transcriptional regulator (copY), a putative metal-binding chaperone (copZ) and a putative copper-transporting P-type ATPase (copB). Transcription analyses demonstrated that copZ and copB are co-transcribed, and transcript levels were increased significantly in response to exposure to high levels of Cu(2+), suggesting that the transport system is operating for copper efflux. Proteomic analysis of Fer1 cells exposed to Cu(2+) revealed the induction of stress proteins associated with protein folding and DNA repair (including RadA, thermosome and DnaK homologues), suggesting that 'Ferroplasma acidarmanus' Fer1 uses multiple mechanisms for resistance to high levels of copper.

Characterization of Ferroplasma isolates and Ferroplasma acidarmanus sp. nov., extreme acidophiles from acid mine drainage and industrial bioleaching environments

Three recently isolated extremely acidophilic archaeal strains have been shown to be phylogenetically similar to Ferroplasma acidiphilum Y(T) by 16S rRNA gene sequencing. All four Ferroplasma isolates were capable of growing chemoorganotrophically on yeast extract or a range of sugars and chemomixotrophically on ferrous iron and yeast extract or sugars, and isolate "Ferroplasma acidarmanus" Fer1(T) required much higher levels of organic carbon. All four isolates were facultative anaerobes, coupling chemoorganotrophic growth on yeast extract to the reduction of ferric iron. The temperature optima for the four isolates were between 35 and 42 degrees C and the pH optima were 1.0 to 1.7, and "F. acidarmanus" Fer1(T) was capable of growing at pH 0. The optimum yeast extract concentration for "F. acidarmanus" Fer1(T) was higher than that for the other three isolates. Phenotypic results suggested that isolate "F. acidarmanus" Fer1(T) is of a different species than the other three strains, and 16S rRNA sequence data, DNA-DNA similarity values, and two-dimensional polyacrylamide gel electrophoresis protein profiles clearly showed that strains DR1, MT17, and Y(T) group as a single species. "F. acidarmanus" Fer1(T) groups separately, and we propose the new species "F. acidarmanus" Fer1(T) sp. nov.

Growth in sulfidic mineral environments: metal resistance mechanisms in acidophilic micro-organisms

Acidophilic micro-organisms inhabit some of the most metal-rich environments known, including both natural and man-made ecosystems, and as such are ideal model systems for study of microbial metal resistance. Although metal resistance systems have been studied in neutrophilic micro-organisms, it is only in recent years that attention has been placed on metal resistance in acidophiles. The five metal resistance mechanisms identified in neutrophiles are also present in acidophiles, in some cases utilizing homologous proteins, but in many cases the degree of resistance is greater in acidophiles. This review summarizes the knowledge of acidophile metal resistance and presents preliminary in silico studies on a few known metal resistance systems in the sequenced acidophile genomes.