Physiological and Genetic Characterization of Thiobacillus Ferrooxidans Strains Used in Biohydrometallurgy

Abstract

By using pulsed-field gel electrophoresis, hereditary polymorphism of the chromosomal DNA structure was shown in Thiobacillus ferrooxidans strains isolated from natural and biomining environments and cultivated on different inorganic substrates. Each strain was found to be characterized by a unique restriction pattern of chromosomal DNA reflecting changes in its nucleotide sequence arising in the process of adaptation to specific environmental conditions. Some strains exhibited nonhereditary alterations in chromosomal DNA developing in response to switching to a different oxidation substrate or in the course of adaptation to high concentrations of metal ions. Increased metal resistance of such strains was found to correlate with the number of copies of resistance genes. Amplification of DNA fragments hosting resistance genes disappeared in repeated transfers of strains on the medium lacking the given inducer. With other strains, however, no structural alterations in the chromosomal DNA were detected with the change of the oxidation product. Different mechanisms by which bacterial activity under extreme conditions could be controlled are considered. A significant variation potential of the T. ferrooxidans genome and a wide range of its adaptability under changing environmental conditions suggest that selection of highly efficient natural strains and their adaptation to specific ecological conditions are of major importance for biohydrometallurgy. This puts into question the prospects of constructing recombinant strains for efficient application in biohydromelallurgical processes.

Keywords:

• Pulsed-field gel electrophoresis (PFGE)
• restriction patterns
• genome variability
• metal resistance