A rapid ATP-based method for determining active microbial populations in mineral leach liquors

An empirical technique for the rapid assessment of active biomass of acidophilic microorganisms in pure cultures and in leach liquors from mineral bio-processing operations is described. The method is based on the measurement of ATP concentrations in test solutions, using commercially-available kits and a portable luminometer. The ATP contents of five Gram-negative biomining bacteria mineral-degrading acidophiles assayed varied from 0.87 × 10−20 to 18 × 10−20 mol per cell in actively-growing cultures. Depletion of ferrous iron in cultures of a strain of Leptospirillum ferriphilum resulted in rapid mortality of the iron-oxidizing bacterium (denoted by decreasing numbers of plate isolates) and corresponding changes in ATP concentrations in culture aliquots. The technique was applied successfully to mineral leachates from stirred tank biomining operations, where it was shown to determine populations of active microorganisms in liquors where most of the cells present were not viable. The method is highly sensitive (detecting as few as 103 acidophiles ml−1 of test solution) and would therefore have generic application in monitoring microbial populations in other types of biomining operations, such as heap bioreactors.