The Chromosomal Arsenic Resistance Genes of Thiobacillus ferrooxidans Have an Unusual Arrangement and Confer Increased Arsenic and Antimony Resistance to Escherichia coli

Abstract

The chromosomal arsenic resistance genes of the acidophilic, chemolithoautotrophic, biomining bacterium Thiobacillus ferrooxidans were cloned and sequenced. Homologues of four arsenic resistance genes, arsB, arsC, arsH, and a putative arsR gene, were identified. The T. ferrooxidans arsB (arsenite export) and arsC (arsenate reductase) gene products were functional when they were cloned in an Escherichia coli ars deletion mutant and conferred increased resistance to arsenite, arsenate, and antimony. Therefore, despite the fact that the ars genes originated from an obligately acidophilic bacterium, they were functional in E. coli. Although T. ferrooxidans is gram negative, its ArsC was more closely related to the ArsC molecules of gram-positive bacteria. Furthermore, a functional trxA (thioredoxin) gene was required for ArsC-mediated arsenate resistance in E. coli; this finding confirmed the gram-positive ArsC-like status of this resistance and indicated that the division of ArsC molecules based on Gram staining results is artificial. Although arsH was expressed in an E. coli-derived in vitro transcription-translation system, ArsH was not required for and did not enhance arsenic resistance in E. coli. The T. ferrooxidans ars genes were arranged in an unusual manner, and the putative arsR and arsC genes and the arsBH genes were translated in opposite directions. This divergent orientation was conserved in the four T. ferrooxidans strains investigated.Thiobacillus ferrooxidans is an acidophilic (optimum pH, 1.8 to 2.5), obligately chemolithotrophic bacterium that obtains its energy through oxidation of ferrous iron to ferric iron or oxidation of reduced inorganic sulfur compounds to sulfuric acid. It is a member of a consortium of bacteria (which includes Thiobacillus caldus and Leptospirillum ferrooxidans) that is used in commercial biooxidation processes to recover gold from arsenopyrite ores (22). Although recent analysis of microbial populations in continuous-flow biooxidation tanks has revealed that T. ferrooxidans may not be as dominant as was once thought, this organism is nevertheless usually present in such tanks (21). Total arsenic levels greater than 13 g liter Ϫ1 may be present in arsenopyrite biooxidation tanks, and therefore the microorganisms present must have a mechanism of resistance to arsenic (8).Plasmid-associated arsenic efflux resistance mechanisms have been known for many years and have been extensively reviewed (5,23,(30)(31)(32)35). Although the number of components of these systems varies, in the case of Escherichia coli plasmids R773 and R46, as well as Acidiphilium multivorum plasmid pKW301 (34), as many as five genes (arsRDABC) are present. In the case of R773, the genes are transcribed in a single operon. The arsR and arsD genes encode repressors that control the basal and upper levels of ars operon expression, while the arsABC genes encode the structural components of the arsenic resistance mechanism. ArsA is an ATPase which forms a complex with ArsB, the transmembrane arsenite efflux p...

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

“…Despite the physiological differences and the reversed membrane potential, the At. ferrooxidans ArsB was functional in E. coli (Butcher et al, 2000). At.…”

“…ferrooxidans appears to lack a gene homologous to E. coli arsA, but contains the arsRBC genes in an unusual configuration ( Fig. 2; Butcher et al, 2000). By Southern hybridization two sets of arsenic resistance operons have been identified from At.…”

“…caldus and A. multivorum ( Fig. 2) and all three operons conferred As(III) resistance in E. coli (Butcher et al, 2000;de Groot et al, 2001;Suzuki et al, 1998). The At.…”

Aplicaciones biotecnológicas en minería aurífera: Estado del arte sobre la oxidación bacteriana de arsenopirita (FeAsS)

“…Esto permite un mecanismo de eliminación de arsénico que se produce cuando la arsenato-reductasa (arsC) reduce el arsénico en el interior de la célula y una bomba específica de salida de arsénico (arsB) saca éste ion, fuera de la célula, a través de la membrana citoplasmática. Un mecanismo similar fue identificado para A. ferrooxidans (Butcher et al 2000), para L. ferriphilum (Tuffin et al 2006) y para L. ferrooxidans (Corkhill et al 2008) quienes observaron, también, que L. ferrooxidans es capaz de soportar una concentración mucho mayor de arsénico, en comparación con los demás microorganismos.…”

The divergent chromosomal ars operon of Acidithiobacillus ferrooxidans is regulated by an atypical ArsR protein

“…Acidithiobacillus ferrooxidans has been shown to contain genes for arsenic resistance on its chromosome (Butcher et al, 2000). Arsenic-resistance genes have been found on both the chromosomes and plasmids of various bacteria, and arsenic resistance has been reviewed extensively (Rosen, 1999 ;Xu et al, 1998 ;Tsai et al, 1997 ;Silver & Phung, 1996 ;Cervantes et al, 1994).…”