Microbial sulphate reduction at a low pH.

It is now well established that microbial sulphate-reduction can proceed in environments with a pH<5. This review summarizes existing reports on sulphate reduction at low pH and discusses possible pH effects on sulphate-reducing bacteria. Microbial sulphate reduction has been observed in acidic lakes, wetlands, mesocosms, acidic sulphate soils and bioreactors. Possible inhibitory factors include the metabolites H(2)S and organic acids, which can be toxic depending on pH. Metal sulphide precipitation and competition with other bacteria, namely iron-reducing bacteria, can inhibit sulphate reduction. Theoretical considerations show that normal sulphate reduction rates are too low to maintain a neutral micro niche in an acidic environment. The first acidotolerant sulphate-reducing bacteria have been isolated recently.