Sulfur cycling in mixed cultures of sulfide-oxidizing and sulfate- or sulfur-reducing oil field bacteria

Abstract

Thiomicrospira strain CVO and Arcobacter strain FWKO B are two nitrate-reducing, sulfide-oxidizing bacteria (NR-SOB) isolated from the Coleville field in western Canada. Analysis by reverse sample genome probing (RSGP) indicates that both can be enriched from Coleville produced water samples by addition of nitrate. Neither could be enriched from waters produced from oil fields with a high resident temperature (40-60°C). In co-cultures of the two microorganisms, CVO dominated at lower and FWKO B at higher sulfide concentrations. Sulfide concentrations of up to 15 mM (480 ppm) could be controlled (i.e., reduced to lower values) by the co-culture. Mixed cultures of a sulfate-reducing bacterium (Desulfovibrio strain Lac6) and CVO or FWKO B produced considerably less sulfide than cultures of Lac6 alone, indicating that these NR-SOB can efficiently oxidize sulfide generated by sulfate reduction provided nitrate is present. The same observations were made for mixed cultures of a sulfur-oxidizing bacterium (Desulfuromonas acetoxidans) and CVO. The results indicate that successful nitrate-mediated conversion of sulfide to oxidized forms (sulfur, sulfate) in oil field production waters by NR-SOB requires the absence of high concentrations of electron donors (e.g., lactate, acetate) that can reverse the nitrate-mediated oxidation reaction.