| Acidithiobacillus ferrooxidans (formerly Thiobacillus ferrooxidans) is the predominant microorganism in bioleaching operations involving sulfidic ores as well as in the production of acid mine drainage. Plasmids are widespread in strains of this organism, although they remain cryptic. The effect of the electron donors iron, sulfur and pyrite (FeS 2) on the stability of plasmids in three strains of A. ferrooxidans was investigated. Using an alkaline-detergent method and agarose gel electrophoresis, it was found that plasmids were stable during subculturing in iron medium and sulfur medium for all strains. For pyrite medium, there was an extended lag phase and slow growth, and plasmid stability was found for the one strain examined. The plasmid harboured by strain A1 was found to be present at one copy per cell. The copy number was unaffected by either iron or sulfur as the electron donor. Thus, cryptic plasmids are stable in different strains of A. ferrooxidans, despite repeated subculturing in iron and sulfur media, and possibly in pyrite medium. |
