Life in blue: copper resistance mechanisms of bacteria and archaea used in industrial biomining of minerals.

Industrial biomining processes to extract copper, gold and other metals involve the use of extremophiles such as the acidophilic Acidithiobacillus ferrooxidans (Bacteria), and the thermoacidophilic Sulfolobus metallicus (Archaea). Together with other extremophiles these microorganisms subsist in habitats where they are exposed to copper concentrations higher than 100mM. Herein we review the current knowledge on the Cu-resistance mechanisms found in these microorganisms. Recent information suggests that biomining extremophiles respond to extremely high Cu concentrations by using simultaneously all or most of the following key elements: 1) a wide repertoire of Cu-resistance determinants; 2) duplication of some of these Cu-resistance determinants; 3) existence of novel Cu chaperones; 4) a polyP-based Cu-resistance system, and 5) an oxidative stress defense system. Further insight of the biomining community members and their individual response to copper is highly relevant, since this could provide key information to the mining industry. In turn, this information could be used to select the more fit members of the bioleaching community to attain more efficient industrial biomining processes.

Identification of putative sulfurtransferase genes in the extremophilic Acidithiobacillus ferrooxidans ATCC 23270 genome: structural and functional characterization of the proteins.

Eight nucleotide sequences containing a single rhodanese domain were found in the Acidithiobacillus ferrooxidans ATCC 23270 genome: p11, p14, p14.3, p15, p16, p16.2, p21, and p28. Amino acids sequence comparisons allowed us to identify the potentially catalytic Cys residues and other highly conserved rhodanese family features in all eight proteins. The genomic contexts of some of the rhodanese-like genes and the determination of their expression at the mRNA level by using macroarrays suggested their implication in sulfur oxidation and metabolism, formation of Fe-S clusters or detoxification mechanisms. Several of the putative rhodanese genes were successfully isolated, cloned and overexpressed in E. coli and their thiosulfate:cyanide sulfurtransferase (TST) and 3-mercaptopyruvate/cyanide sulfurtransferase (MST) activities were determined. Based on their sulfurtransferase activities and on structural comparisons of catalytic sites and electrostatic potentials between homology- modeled A. ferrooxidans rhodaneses and the reported crystal structures of E. coli GlpE (TST) and SseA (MST) proteins, two of the rhodanese-like proteins (P15 and P16.2) could clearly be defined as TSTs, and P14 and P16 could possibly correspond to MSTs. Nevertheless, several of the eight A. ferrooxidans rhodanese-like proteins may have some different functional activities yet to be discovered.