Strain diversity of Thiobacillus ferrooxidans and its significance in biohydrometallurgy

Abstract

Structural changes in chromosomal DNA of Thiobacillus ferrooxidans strains that occur under the influence of varied growth conditions were studied by pulsed-field gel electrophoresis. Strain diversity of T. ferrooxidans was manifested in different growth rates and oxidation rates of inorganic substrates under extreme conditions, in different resistance to metal ions and low pH values, and also in polymorphism of the chromosomal DNA fragments generated by the macrorestriction endonucleases. Adaptation of some strains to growth on media containing new substrates was accompanied by changes in the number and size of restriction fragments. Thus, new 177 and 164 kb DNA fragments were revealed after the substitution of the oxidation substrate from Fe2+ to FeS2 or from Fe2+ to So, respectively, whereas 115 and 77 kb DNA fragments disappeared. The switching from Fe2+ to So resulted in the change in the number of 27 kb DNA fragments. Another type of chromosomal DNA variability was found in the strains adapted to high concentrations of metal ions. A comparison of XbaI-restriction patterns in parent strains and in strains with acquired enhanced resistance to zinc (from 40 to 70 g/l) or arsenic (from 1.5 to 4.0 g/l) revealed amplification of 98 and 28 kb fragments, respectively. When both strains were subcultured on medium with Fe2+ without the inducing factors, amplification of DNA fragments was no longer detectable. However, the strain adapted tp 50 g/l of Fe2+/Fe3+ had a mutation in the structure of chromosomal DNA. The data obtained on the natural and experimental genomic variability of T. ferrooxidans strains provide biotechnologists with practical recommendations for selection aimed at the intensification of bioleaching processes and testify about possibilities of strain monitoring in natural and technological conditions. Strains with the labile genome have an advantage in biohydrometallurgy.