BACTERIAL-POPULATIONS IN SAMPLES OF BIOLEACHED COPPER ORE AS REVEALEDBY ANALYSIS OF DNA OBTAINED BEFORE AND AFTER CULTIVATION

The composition of bacterial populations in copper bioleaching systems was investigated by analysis of DNA obtained either directly from ore s or leaching solutions or after laboratory cultures, This analysis co nsisted of the characterization of the spacer regions between the 16 a nd 23S genes in the bacterial rRNA genetic loci after PCR amplificatio n, The sizes of the spacer regions, amplified from DNAs obtained from samples, were compared with the sizes of those obtained from cultures of the main bacterial species isolated from bioleaching systems, This allowed a preliminary assessment of the bacterial species present in t he samples, Identification of the bacteria was achieved by partial seq uencing of the 16S rRNA genes adjacent to the spacer regions, The spac er regions observed in DNA from columns leached at different iron conc entrations indicated the presence of a mixture of different bacteria, The spacer region corresponding to Thiobacillus ferrooxidans was the m ain product observed at high ferrous iron concentration, At low ferrou s iron concentration, spacer regions of different lengths, correspondi ng to Thiobacillus thiooxidans and ''Leptospirillum ferrooxidans'' wer e observed, However, T. ferrooxidans appeared to predominate after cul ture of these samples in medium containing ferrous iron as energy sour ce, Although some of these strains contained singular spacer regions, they belonged within previously described groups of T. ferrooxidans ac cording to the nucleotide sequence of the neighbor 16S rRNA, These res ults illustrate the bacterial diversity in bioleaching systems and the selective pressure generated by different growth conditions.