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Adaptive laboratory evolution (ALE) was employed to isolate arsenate and copper cross-resistant strains, from the copper-resistant M. sedula CuR1. The evolved strains, M. sedula ARS50-1 and M. sedula ARS50-2, contained 12 and 13 additional mutations, respectively, relative to M. sedula CuR1. Bioleaching capacity of a defined consortium (consisting of a naturally occurring strain and a genetically engineered copper sensitive strain) was increased by introduction of M. sedula ARS50-2, with 5.31 and 26.29% more copper recovered from enargite at a pulp density (PD) of 1 and 3% (w/v), respectively. M. sedula ARS50-2 arose as the predominant species and modulated the proportions of the other two strains after it had been introduced. Collectively, the higher Cu 2+ resistance trait of M. sedula ARS50-2 resulted in a modulated microbial community structure, and consolidating enargite bioleaching especially at elevated PD.

The ubiquity of arsenic in the environment has led to the evolution of enzymes for arsenic detoxification. An initial step in arsenic metabolism is the enzymatic reduction of arsenate [As(V)] to arsenite [As(III)]. At least three families of arsenate reductase enzymes have arisen, apparently by convergent evolution. The properties of two of these are described here. The first is the prokaryotic ArsC arsenate reductase of Escherichia coli. The second, Acr2p of Saccharomyces cerevisiae, is the only identified eukaryotic arsenate reductase. Although unrelated to each other, both enzymes receive their reducing equivalents from glutaredoxin and reduced glutathione. The structure of the bacterial ArsC has been solved at 1.65 Å. As predicted from its biochemical properties, ArsC structures with covalent enzyme-arsenic intermediates that include either As(V) or As(III) were observed. The yeast Acr2p has an active site motif HC( X)5R that is conserved in protein phosphotyrosine phosphatases and rhodanases, suggesting that these three groups of enzymes may have evolved from an ancestral oxyanion-binding protein.

The ACR2 gene of Saccharomyces cerevisiae was disrupted by insertion of a HIS3 gene. Cells with the disruption were sensitive to arsenate. This phenotype could be complemented by ACR2 on a plasmid. The ACR2 gene was cloned and expressed in Escherichia coli as a malE gene fusion with a C-terminal histidine tag. The combination of chimeric MBP-Acr2-6H protein and yeast cytosol from an ACR2-disrupted strain exhibited arsenate reductase activity.

The Burkholderia xenovorans LB400 multireplicon genome displays a relatively high proportion of redundant genes, including several genes predicted to be related to arsenic resistance. These comprise an ars gene cluster, composed of the arsR3, acr3, arsC1 and arsH genes, as well as two arsB, arsC2, and seven individual arsR genes. The objective of this work was to elucidate the involvement of the ars gene cluster in arsenic resistance by the LB400 strain. Susceptibility tests showed that B. xenovorans LB400 is highly resistant to arsenate and arsenite. Arsenic resistance was induced by prior exposure of LB400 to arsenate or arsenite. reverse transcription-polymerase chain reaction assays using total RNA from LB400 showed arsenite-induced transcription of the arsR3 gene, suggesting that the ars gene cluster constitutes an arsenite-responsive operon. Transfer of cloned LB400 ars genes to heterologous Escherichia coli or Pseudomonas aeruginosa strains demonstrated that the ArsR3 transcriptional repressor, ArsC1 arsenate reductase, and the Acr3 arsenite efflux pump encoded in the LB400 ars gene cluster, are all associated to the arsenic resistance phenotype of this strain.Graphical AbstractThe ars gene cluster from Burkholderia xenovorans LB400 is responsible for the inducible arsenic-resistance phenotype of the bacterium.

A novel aerobic bacterium, strain HT23 T , able to grow on 500 mM sodium arsenate was isolated from a hot-spring sediment sample collected from Athamallik, Orissa, India. Cells of this isolate were Gram negative. Heterotrophic growth was observed at pH 6.0–11.0 and 20–45 °C. Optimum growth was observed at 37 °C and pH 7.0–10.0. The major polar lipids are diphosphatidyl glycerol, phosphatidyl glycerol, phosphatidyl ethanolamine, phosphatidyl choline and phosphatidyl monomethyl ethanolamine. The major isoprenoid quinone was Q-10. 16S rRNA gene sequence analysis indicated that the bacterium clustered with the genus Pannonibacter and showed 98.9 % similarity with Pannonibacter phragmitetus C6-19 T (DSM 14782 T ) and 98 % with the P. phragmitetus group B and P. phragmitetus group E strains. Levels of DNA–DNA relatedness between the strain HT23 T and P. phragmitetus C6-19 T (DSM 14782 T ) and other strains of P. phragmitetus group B and group E strains were below 55 %. On the basis of phenotypic and chemotaxonomic characteristics, 16S rRNA gene sequence analysis and DNA–DNA hybridization data, strain HT23 T is considered to represent a novel species of the genus Pannonibacter , for which the name Pannonibacter indica sp. nov. is proposed. The type strain is HT23 T (=JCM 16851 T  = DSM 23407 T  = LMG 25769 T ).

• The role of arbuscular mycorrhizal fungi (AMF) in arsenate resistance in arbuscular mycorrhizal associations is investigated here for two Glomus spp. isolated from the arsenate-resistant grass Holcus lanatus. • Glomus mosseae and Glomus caledonium were isolated from H. lanatus growing on an arsenic-contaminated mine-spoil soil. The arsenate resistance of spores was compared with nonmine isolates using a germination assay. Short-term arsenate influx into roots and long-term plant accumulation of arsenic by plants were also investigated in uninfected arsenate resistant and nonresistant plants and in plants infected with mine and nonmine AMF. • Mine AMF isolates were arsenate resistant compared with nonmine isolates. Resistant and nonresistant G. mosseae both suppressed high-affinity arsenate/phosphate transport into the roots of both resistant and nonresistant H. lanatus. Resistant AMF colonization of resistant H. lanatus growing in contaminated mine spoil reduced arsenate uptake by the host. • We conclude that AMF have evolved arsenate resistance, and conferred enhanced resistance on H. lanatus.

Arsenate resistance has been used for screening for photosynthetic mutants of Chlamydomonas, since photosynthetic mutants, such as CC981 defective in phosphoribulokinase, were shown to have arsenate resistance. Also, another type of arsenate-resistant mutants, including AR3 that lacks a homolog of a phosphate (Pi) transporter, PTB1, has been isolated. We investigated the uptake of Pi and arsenate, and the gene expression of Pi transporters, which are involved in both Pi and arsenate transport, in mutants CC981 and AR3. In the wild type, both Pi and arsenate uptake were initially high, but were inactivated in the presence of arsenate with time, especially in the dark. In contrast, both mutants were shown to exhibit higher Pi uptake, but lower arsenate uptake than the wild type, regardless of the presence or absence of light. Then, the gene expression of Pi transporters in the cells used for the uptake measurements was investigated and compared between the mutants and the wild type. In CC981, the mRNA levels of PTA2 and PTA4 were higher, while those of PTB3 and PTB5 were lower, as compared with in the wild type. In AR3, those of PTA2 and PTB2 were higher, but that of PTB5 was lower than in the wild type. These findings suggest that the arsenate resistance shown by the mutants in light is due to reduction of arsenate uptake probably through the downregulation of some Pi transporter expression, while the Pi uptake maintained even in the dark is possibly related to higher expression of other Pi transporter(s) than in the wild type.

The ACR2 gene of Saccharomyces cerevisiae was disrupted by insertion of a HIS3 gene. Cells with the disruption were sensitive to arsenate. This phenotype could be complemented by ACR2 on a plasmid. The ACR2 gene was cloned and expressed in Escherichia coli as a malE gene fusion with a C-terminal histidine tag. The combination of chimeric MBP-Acr2-6H protein and yeast cytosol from an ACR2-disrupted strain exhibited arsenate reductase activity.

Twenty years ago, V. P. Skulachev put forward the revolutionary concept of the chemiosmotic sodium cycle which is an integral of the paradigm of modern bioenergetics. This fundamental concept stimulated studies in many areas and yielded plenty of sometimes quite unexpected (and thus most valuable) discoveries. In particular, variations of the sodium cycle have been found in a surprisingly large number of pathogenic microorganisms, raising the question about the possible link of sodium energetics and virulence. This brief review discusses some paradoxes related to the Na(+) cycle in an important human pathogen, Vibrio cholerae.

Terribacillus sp. AE2B 122 is an environmental strain isolated from olive-oil agroindustry wastes. This strain displays resistance to arsenic, one of the most ubiquitous carcinogens found in nature. Terribacillus sp. AE2B 122 possesses an unusual ars operon, consisting of the transcriptional regulator (arsR) and arsenite efflux pump (arsB) but no adjacent arsenate reductase (arsC) locus. Expression of arsR and arsB was induced when Terribacillus was exposed to sub-lethal concentrations of arsenate. Heterologous expression of the arsB homologue in Escherichia coli ∆arsRBC demonstrated that it conferred resistance to arsenite and reduced the accumulation of arsenic inside the cells. Two members of the arsC-like family (Te3384 and Te2854) found in the Terribacillus genome were not induced by arsenic, but their heterologous expression in E. coli ∆arsC and ∆arsRBC increased the accumulation of arsenic in both strains. We found that both Te3384 and Te2854 slightly increased resistance to arsenate in E. coli ∆arsC and ∆arsRBC, possibly by chelation of arsenic or by increasing the resistance to oxidative stress. Finally, arsenic speciation assays suggest that Terribacillus is incapable of arsenate reduction, in agreement with the lack of an arsC homologue in the genome.