Sulfate reduction and trichloroethylene biodegradation by a marine microbial community from hydrothermal vents sediments

Sulfate reduction (SR) and trichloroethylene (TCE) biodegradation at two different temperatures (37 and 70 °C) were investigated in enrichment cultures prepared with two different samples of sediments collected from hydrothermal vents. The unadapted sediments were incubated with sulfate (4 g L⁻¹) as the electron acceptor before TCE addition to enrich them in biomass and to establish a constant sulfate reduction (SR, 87% sulfate conversion and specific H₂S concentration of 90.81 ± 8.19 mg H₂S g VSS⁻¹), afterwards TCE was added at an initial concentration of 300 ??mol L⁻¹. The best results for TCE biodegradation were obtained at 37 °C. At this temperature, SR was up to 92%, whereas TCE biodegradation reached 75% and ethane was detected as the main degradation product. Under thermophilic conditions (70 °C) TCE biodegradation reached up to approximately 60% and the SR was 30% in 30 days of incubation with the chlorinated solvent. Along with these results, the 16S rDNA analysis from samples at 37 °C showed the presence of bacteria belonging to the genera: Clostridium, Bacillus and Desulfuromonas. The overall results on TCE degradation and SR suggest that cometabolic TCE degradation is carried out by sulfate or sulfur reducers and fermentative bacteria at mesophilic conditions.