Microbial behaviour under conditions relevant to heap leaching: Studies using the sulfur-oxidising, moderate thermophile Acidithiobacillus caldus

The responses of Acidithiobacillus (At.) caldus to solution additives and varied acidity have been examined in growth media containing tetrathionate. It was found that increased pH in the range of pH 4–7.5 and increased concentrations of selected inorganic salts and an organic compound in various ranges from 1 to 40 g L− 1 (ionic strengths 0.02–0.86 M) typically caused prolonged delays in tetrathionate oxidation and lower specific growth rates. In general, total cell numbers decreased with increased salt concentrations, consistent with there being an increased energy requirement for cell maintenance and a concomitant decrease in cell replication in increasingly inhospitable environments. The data generated in this study add to our knowledge of the responses of At. caldus to solution compositions that might be encountered in heap leaching systems. Through comparison with other studies, the data also show that responses are sometimes species specific. A database of microbial responses of known bioleaching microorganisms to quantified constituents in leaching solutions makes the use of periodic solution chemistry data and cell enumeration to assess ‘heap health’ more credible.