Diversity amongst Bacillus merA genes amplified from mercury resistant isolates and directly from mercury polluted soil

Mercury resistant (HgR) Bacillus were isolated from soil at a mercury contaminated site on the banks of the River Mersey, in Northwest England. The frequency of HgR bacteria in the culturable Bacillus population in soil samples ranged from 4.4% to 5.4%. No HgRBacillus could be isolated from a sediment sample taken close to the contaminated soil sample in 1994. DNA sequences homologous to a merA probe from the HgR isolate Bacillus sp. strain RC607 were found to be chromosomally located in 98% of the HgRBacillus isolates from the soil site. Oligonucleotide primers designed to the merA gene of RC607 were used to amplify the sequences present in the isolates, and also merA determinants present in bacterial DNA directly extracted from soil. Classification of cultured Bacillus merA products and of 40 merA determinants amplified directly from extracted soil bacterial DNA was based on restriction fragment length polymorphism patterns. This technique revealed a total of 22 classes of amplification products. Unweighted paired group mean analysis was used to examine the relationships between these classes and indicated the presence of microsites in Fiddlers Ferry soil containing distinct HgR populations. API identification of the HgRBacillus isolates revealed that diversity of merA between these microsites is not simply due to the divergent evolution of differing Bacillus species. Lack of a more substantial class correlation between cultured samples taken at different times indicated significant temporal variation in the genetic composition of Bacillus merA in soil.