Evaluation of enrichments of sulfate reducing bacteria from pristine hydrothermal vents sediments as potential inoculum for reducing trichloroethylene

The evaluation of enrichments from pristine hydrothermal vents sediments on its capability of reducing trichloroethylene (TCE) under sulfate reducing conditions with lactate and volatile fatty acids (VFAs) as substrates was performed. Effect of the possible TCE biodegradation intermediates cis and trans 1,2 dichloroethenes on sulfate reduction (SR) was also evaluated. The influence of cyanocobalamin (CNB₁₂) and riboflavin (RF) on the SR and biodegradation of TCE was also determined. Sediments from the vents were incubated at 37°C and supplemented with 4 g l^-1 SO₄^2-, lactate or VFAs and amended in the corresponding treatments with either CNB₁₂ or RF in separated experiments. A percentage of TCE removal of 86 (150 μmol l^-1 initial concentration) was attained coupled to 48% sulfate depletion with lactate as substrate. Up to 93% removal of TCE (300 μmol l^-1 initial concentration) and 40% of sulfate was reached for VFAs as electron donor. A combination of lactate and CNB₁₂ yielded the best SR. The overall results suggest a syntrophic association in this microbial community in which sulfate reducers, dehalogenating, and probably halorespiring bacteria may be interacting and taking advantage of the fermentation of substrates differently, but without interruption of SR in spite of the fact that TCE was always present. It was also clear that sulfate reduction must be established in the cultures before any degradation can occur. The microbial community present in these hydrothermal vents sediments could be a new source of inoculum for bioreactors designed for dechlorination purposes.