Aluminium sulphate and potassium nitrate effects on batch culture of iron oxidising bacteria

Batch culture techniques and a kinetic model were used to examine the effects of Al3+ and NO3− ions on the cell replication rates of iron oxidising bacteria. Aluminium ions at a concentration of 2240 ppm (85 mM) were shown to reduce the cell replication rate to 85% of that observed for cells in minimal media. Nitrate ions (NO3−) at a concentration of 920 ppm (15 mM) were shown to reduce the cell replication rate to 65% of that observed for cells cultured in minimal media and the culture was not viable beyond three sequential batch culture cycles. The inhibition produced by nitrate is greater than that previously observed for chloride ions, but the impact of aluminium is similar to that observed with salts such as potassium, sodium and ammonium sulphate i.e. a small reduction in replication rate associated with increased concentration but without long term effects on culture viability. The results of this study are significant for South American bio-leach operations that have reported elevated concentrations of Al3+ ions in process water. The impact of varying substrate (FeSO4) concentration was also examined; it was found that iron oxidising cells are subject to substrate inhibition.