Occurrence of acidophilic halotolerant Fe(II)-oxidizing microorganisms in a marine shore mine tailings deposit at Chañaral, Atacama desert, northern Chile

A marine shore copper mine waste tailings deposit in arid climate at Chañaral, Chile was studied to understand the influence of high salinity on the microbial community composition and biogeochemical processes in this extreme environment. Samples were taken from the oxidized zone at several sites which had a paste pH in the range of 2-8. The microbial community was quantitatively analyzed using different methods: 1) total cell numbers by SYBR Green II direct counting, 2) quantitative real-time PCR (Q-PCR), 3) most probable number cultivation of acidophilic Fe(II)-oxidizers. The results showed that the composition of microbial communities and the cell numbers of different microbial groups are highly variable at different sampling sites. Depth profiles of cell numbers of the mine tailing deposit showed total cell numbers in the range of 104 - 108 cells g-1 tailings. Bacteria dominated over Achaea in the mine tailings. The acidophilic Fe(II)- and/or sulfur-oxidizing Acidithiobacillus spp. dominated over the acidophilic Fe(II)-oxidizing Leptospirillum spp. among the Gram-negative Bacteria. In parallel to the microbial community analyses, novel acidophilic halotolerant Fe(II)-oxidizing microorganisms were enriched at salt concentrations of up to 1 M probably suitable for metal bioleaching using seawater. The growth of these microorganisms and its ability to oxidize ferrous iron were dependent on pH, temperature, inoculum and initial concentration of ferrous iron. The cell density decreased after three weeks of incubation since most likely high ferric to ferrous iron ratios had an inhibitory effect on cell growth. Ferrous iron was completely oxidized, while the cell numbers were up to 107 cells/ml. The bioleaching potential of the enrichment cultures is currently under evaluation.

کلیدواژه ها:

Acidithiobacillus spp. ، iron oxidation ، arid climate ، chalcopyrite ، halotolerant ، mine tailings