IMPLICATION OF MOLECULAR TOOLS TO DETECT AND QUANTIFY ARSENATE REDUCTION IN ESTUARINE SEDIMENTS

Arsenic is an ubiquitous contaminant due to natural releases from volcanic and marine sedimentary rocks and anthropogenic inputs from mining, chemical and power industry and agricultural applications. Arsenate (+5) and arsenite (+3) are found in aquatic environments as dominant inorganic forms depending on the prevailing redox conditions. The biogeochemical cycle of arsenic strongly depends on microbial transformation comprising oxidation, reduction, and methylation. Microbial dissimilatory reduction of arsenate is especially important process in anoxic environments. Dissimilatory arsenate reducing bacteria were isolated from various ecological niches and their enzymes and genes were recently found. To detect in situ microbial activities involved in arsenate reduction in the environment, we examine arsenate reductase genes (arrA) in estuarine sediments. Degenerate primers targeting arrA genes were designed using the sequences from the Genbank database. PCR amplification with the primers detected putative arrA genes from arsenate reducing enrichment cultures and estuarine sediments obtained from Chesapeake Bay. The genes found in the enrichment cultures and in the sediments were clustered as distinct groups depending on their geographical and ecological locations. Thus, the sequence analysis of arrA genes showed the presence of distinct arsenate reducing microbial communities in different environments. Furthermore, genetic probes targeting the arrA genes detected from Chesapeake Bay sediments were designed to monitor the changes of arsenate reducing communities and their gene expression in arsenate reducing enrichment cultures using Q-PCR.