The use of sulfate-reducing bacteria (SRB) is a cost-effective route to treat sulfate- contaminated waters and precipitate metals. The isolation and characterization of a SRB strain from an AMD in a Brazilian tropical region site was carried out. With a moderately acidic pH (5.5), the C.1 strain began its growth and with continued growth, modified the pH accordingly. The strain under these conditions reduced sulfate at the same rate as an experiment performed using an initial pH of 7.0. The dsrB gene-based molecular approach was used for the characterization of this strain and its phylogenetic affiliation was similar to genus Desulfovibrio sp. The results show an SRB isolate with unexpected sulfate reducing capacity in moderately acidic conditions, bringing new possibilities for the treatment of AMD, as acid water would be neutralized to a mildly acidic condition.

RESUMO A biolixiviação de minérios de baixo teor e com elevado conteúdo de impurezas tem se mostrado alternativa importante para o aproveitamento destes, uma vez que a recuperação do metal por métodos pirometalúrgicos convencionais mostra-se economicamente inviável. A identificação e quantificação dos micro-organismos capazes de promover a biolixiviação mostram-se estratégicas para alcançar bons rendimentos no controle do processo e na recuperação de metais. Nesse sentido, as técnicas de biologia molecular são as ferramentas mais utilizadas para tal propósito. Este trabalho, utilizando técnicas de reação em cadeia da polimerase (PCR), polimorfismos de comprimento dos fragmentos de restrição (RFLP) e reação em cadeia da polimerase seguida de eletroforese em gel com gradiente desnaturante (PCR-DGGE), mostrou que a diversidade nas colunas de biolixiviação de cobre estudadas é baixa e que a temperatura é importante na manutenção de determinadas espécies, havendo predominância de Acidithiobacillus ferroxidans a 35°C e de Sulfobacillus thermosulfidooxidans a 50°C.

Acid mine drainage (AMD) waters are highly acidic (pH < 4), contain high concentrations of sulfate and dissolved metals, and are very toxic to many living organisms. The development of technologies to treat sulfate contaminated wastewaters by using sulfate-reducing bacteria (SRB) has produced a cost-effective route to treat AMD. Notwithstanding, the SRB sensitivity to acid limits their use in AMD remediation. In the current study, acidophilic strains of SRB were isolated from an AMD followed by their molecular characterization. One SRB-culture was able to grow at pH 4.5 in Postgate C modified medium containing ethanol as carbon source, indicating that such bacterium has the potential for the bioremediation of acidic waters. Following, the strains were characterized by molecular biology techniques. The characterization was done by PCR amplification, cloning and sequencing of the genes coding for parts of the alpha and beta subunits of dissimilatory sulfite reductase (dsrAB) and hydrogenase (hyd), which encode key enzymes of the SRB energy metabolism. Phylogenetic analysis suggested a line of SRB descent from the delta-Proteobacteria among the strains identified as Desulfovibrio fructosovorans.