Isolation Of Sulfate-Reducing Bacteria From Heavy Metal-Contaminated Sediments And Their Ability To Reduce Arsenate

Arsenic compounds are common, toxic, and carcinogenic environmental pollutants. The toxicity, bioavailability, chemical speciation and transformation processes of arsenic in environmental media are closely related to their chemical forms. In recent years, arsenic pollution has become one of the global environmental problems. Microbes play an important role in arsenic transformation processes. For example, sulfate-reducing bacteria(Sulfate-reducing bacteria, SRB) are important microbial consortia which take a fundamental role in the activation or release of arsenic in anaerobic environments. The arsenic reduction by SRB is closely related to the environmental behavior of arsenic, including the migration, chemical speciation and transformation, and thus is associated with the release of arsenic toxicity to the environment. Therefore, strengthening microbial arsenic transformation and the relevant mechanism in ecological environment is of great scientific significance.In this paper, the microbial community structures in heavy metal-contaminated sediments at Jinzhou Bay were analized and compared by high-throughput pyrosequencing technology and layer plating method based on Mi Seq platform. Then SRB strains were isolated from these sediments and their ability to reduce arsenate was evaluated. The results showed that the microbial diversity and structure changes along with the varying of severity of heavy metal pollution. The diversity of microbial species in sediments containing relatively low concentrations of heavy metal pollutants is higher than that in high concentrations of heavy metal pollutants. In total, 110 sulfate-reducing bacterial strains were isolated by Hungate anaerobic techniques and layer plating method, but these strains belong to three OTU. Three representative sulfate-reducing bacterial strains that can reduce arsenate to arsenite were designated as S2, S3-11, and S13. Analyses of 16 S r RNA gene sequences suggest that these strains are most similar to species from Clostridium. In presence of 1.0 mmol·L-1 As(V), strain S3-11 could reduce 23.4% of arsenate within 10 hours; however, strain S2 and Strain S13 showed relatively higher arsenate reduction efficacy compared to strain S3-11 when 3.0 mmol·L-1 or 5.0 mmol·L-1 was present. Strain S2 could reduce 14.2% of the added 7.0 mmol·L-1 arsenate within 24 h. Strain S2 was a rod-shape, Gram-positive, spore-forming, and strictly anaerobic bacterium. The cells of S2 were 2.0×0.6 μm in size. Strain S2 shares a 99% sequence similarity in 16 S r RNA gene with Clostridium sporogens strain JCM 7849. Sucrose, glucose, sodium formate, sodium acetate, sodium lactate could be used as the sole carbon sourceby strain S2 and the optimum temperature for growth was 30 ℃, optimum p H was 7.0. All the results demonstrate the sulfate-reducing bacteria present in heavy metal-contaminated sediments at Jinzhou Bay could reduce various concentrations of arsenate, suggesting their important role in the microbial transformation of arsenic at this specific site.