The effects of direct electric current on the viability and metabolism of acidophilic bacteria

The application of direct electric current to soil to remove metal ions is an emerging remediation technology. The combination of this approach with bioremediation requires that soil bacteria be viable and metabolically active under the applied currents (20 mA cm(-2)) and their imposed acidic conditions. In this study, sulfur-oxidizing bacteria (SOBs; a mixed culture and pure culture of Thiobacillus ferrooxidans) growing an elemental sulfur, and the acidophilic heterotroph Acidiphilium SJH, growing on glucose, have been chosen as representative organisms. In liquid culture, low cell densities of T. ferroxidans and Acidiphilium SJH were inactivated by the current; however, a high cell density of SOBs was able to recover activity when the current was switched off, and a high density of Acidiphilium SJH was able to grow despite the presence of current. In soil slurries (5, 10, and 30% w/v silt soil), indigenous SOBs were metabolically active in the presence of current, sulfate production was enhanced. There was also enhanced glucose consumption of Acidiphilium SJH in 10 and 30% slurries; however, no protective effect or increased metabolism occurred when T. ferrooxidans was introduced into soil slurries. (C) 1999 Elsevier Science Inc.