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

Abstract

The chromosomal arsenic-resistance (ars) operon of Acidithiobacillus ferrooxidans is atypical in that it is divergent, with its arsCR and arsBH genes transcribed in opposite directions. Furthermore, the amino-acid sequence of the putative ArsR-like regulator of the ars operon is not conserved in regions that have been shown to be responsible for binding to arsenic. Instead, the ArsR-like protein of At. ferrooxidans is related to a group of unstudied ArsRlike proteins that have been found to be associated with chromosomal ars-like operons identified during genome-sequencing projects. Using arsB-lacZ, arsR-lacZ and arsC-lacZ fusions, it was shown that the ArsR-like protein of At. ferrooxidans is a repressor of the arsBH and arsRC genes of this organism, and that induction of gene expression took place when either AsIII (arsenite) or AsV (arsenate) were added. Deletion of 19 aa from the C terminus of the 118 aa ArsR protein did not affect the regulation of its activity, but deletion of an additional 28 aa inactivated ArsR. Northern-blot hybridization suggested that on induction of expression, the arsRC genes were transcribed in greater quantities than the arsBH genes, but that the level of induction was not affected by the form of arsenic added (AsIII or AsV).

An ArsR/SmtB Family Member Is Involved in the Regulation by Arsenic of the Arsenite Oxidase Operon in Thiomonas arsenitoxydans

“…S4 in the supplemental material), the spatial location of the three cysteine residues in the predicted structure of AioF is different from that of the characterized ArsR: in AioF, one cysteine is located upstream from the ␣3 helix and two cysteines are located at the C terminus of the ␣5 helix rather than within or near the ␣3 helix, as in most ArsR proteins (26). Interestingly, As binding sites in Acidithiobacillus ferrooxidans ArsR are located at the end of the ␣5 helix (21), and the induction of the ars genes in this bacterium takes place in the presence of As(III) and As(V), even in the absence of the arsenate reductase-encoding gene, arsC (39). It is therefore possible that the close localization of the two cysteine residues at the C terminus allows the binding not only of As(III) but also of As(V).…”

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

“…As(III) efflux by the ArsB protein; intra/extracellular binding of the metal reducing its toxic effect; exclusion of the metal via a permeability barrier, in this instance the expression of the phosphate-specific transport protein that is specific for phosphate but not As(V); alteration of a cellular component to lower its sensitivity to the toxic metal, for example the less sensitive cytochrome c oxidase in some mercury-resistant strains; and finally conversion of the metal to a less toxic form, an example being the reduction of Hg(II) to Hg(0), which then volatilizes out of the cell. Rawlings, 2002). The presence of the arsB gene (efflux pump) has been identified by Southern hybridization in various acidophilic micro-organisms; these include At.…”

Analysis of Genes Involved in Arsenic Resistance in Corynebacterium glutamicum ATCC 13032

“…1B). Another exception is A. ferrooxidans and Serratia marcescens, where the chromosomal arsenic resistance operon contains two clusters (arsCR-arsBH for A. ferrooxidans and arsBC-arsRH for S. marcescens) which are transcribed in the opposite direction (12). The possible significance of this particular gene organization remains unknown, but a divergent expression could mean an independent or differential regulation to optimize the adaptation of the microorganism to nutritional or environmental changes (9).…”

“…This operon was initially discovered in the E. coli plasmids R773 and R46 (17) and then on plasmid pKW301 from Acidiphilium multivorum (57). In addition to the above-mentioned arsenic resistance operons, a broad diversity of fourgene operons have been described in different species, such as Bacillus subtilis (52), Acidithiobacillus ferrooxidans (11,12), and a Synechocystis sp. (36).…”