Microbial sulfate reduction combined with reductive dechlorination of trichloroethylene in hydrothermal vents sediments

Microbial sulfate reduction (MSR) is a natural process widely used in environmental biotechnology. The applications of MSR include biodegradation of hazardous organic compounds, biotransformation and recuperation of metals and bioremediation of sites damaged by the effect of acid mine drainage (AMD). Sulfate reducing bacteria (SRB) are microorganisms inhabiting a wide variety of environments including places such as deep sea hydrothermal vents and cold, harsh places in the Antarctic. Since these environments are a great source of microbial diversity, it was decided to take samples of shallow hydrothermal vents located in Mexico to carry out research on sulfate reduction and biodegradation of organic pollutants. In this chapter are presented some of the results on MSR and biodegradation of trichloroethylene (TCE) by enrichments of SRB from sediments collected at shallow hydrothermal vents located in Mexico (Punta Mita, Nayarit). The results show that the sediment samples incubated under sulfate reducing conditions can reduce TCE and sulfate simultaneously at 37 and 70°C. Results on 16S rRNA analysis of the TCE degrading sediments showed bacteria closely related to genera Clostridium, Bacillus and Desulfuromonas. Also, it was demonstrated that samples of the hydrothermal vents sediments incubated with sulfate and never exposed to TCE encode α and β subunits of dissimilatory sulfite reductase and that reduction of sulfate to sulfite has been carried out by the SRB in the sediments. Experiments on MSR with some different samples taken at the same hydrothermal vents area suggest that the sulfate reduction and H2S formation might be the result of syntrophies among several microorganisms besides SRB and fermentative bacteria.