Analysis of mercuric reductase (merA) gene diversity in an anaerobic mercury‐contaminated sediment enrichment

Summary The reduction of ionic mercury to elemental mercury by the mercuric reductase (MerA) enzyme plays an important role in the biogeochemical cycling of mercury in contaminated environments by partition- ing mercury to the atmosphere. This activity, common in aerobic environments, has rarely been examined in anoxic sediments where production of highly toxic methylmercury occurs. Novel degenerate PCR primers were developed which span the known diver- sity of merA genes in Gram-negative bacteria and amplify a 285 bp fragment at the 3 end of merA. These primers were used to create a clone library and to analyse merA diversity in an anaerobic sediment enrichment collected from a mercury-contaminated site in the Meadowlands, New Jersey. A total of 174 sequences were analysed, representing 71 merA phy- lotypes and four novel MerA clades. This first exami- nation of merA diversity in anoxic environments suggests an untapped resource for novel merA sequences.