Hydrogen treshold concentrations in pure cultures of halorespiring bacteria and at a site polluted with chlorinated ethenes

Halorespiring microorganisms are not only able to oxidize organic electron donors such as formate, acetate, pyruvate and lactate, but also H-2. Because these microorganisms have a high affinity for H-2, this may be the most important electron donor for halorespiration in the environment. We have studied the role of H-2-threshold concentrations in pure halorespiring cultures and compared them with mixed cultures and field data. We have found H-2-threshold values between 0.05 and 0.08 nM for Sulfurospirillum halorespirans, S. multivorans and Dehalobacter restrictus under PCE-reducing and nitrate-reducing conditions. The reduction of PCE and TCE can proceed at H-2 concentrations of below 1 nM at a polluted site. However, for the reduction of lower chlorinated ethenes a higher H-2 concentration is required. This indicates that the measured H-2 concentration in situ can be an indicator of the extent of anaerobic reductive dechlorination.