Microbial ecology of a mercury-rich hot spring.

摘要

Horizontal gene transfer (HGT) has been observed to occur between archaea and bacteria. The evolution of the mer operon which encodes for mercury resistance in microorganisms has been influenced by HGT. This study focuses on the microbial ecology of Coso Hot Springs (CHS) which contains high concentrations of mercuric sulfide or cinnabar. Specifically, this study was conducted to (a) identify archaeal and bacterial members of the CHS community, (b) determine whether HGT of merA genes occurred between the archaea and bacteria living in CHS and (c) determine the merA gene profile of microorganisms from CHS. Fluorescence in situ hybridization (FISH) analysis showed that the archaea made up 70% and the bacteria constituted 16% of the CHS microbial community. 16S rDNA sequencing identified the archaea in the pool to be Sulfolobus-like, Metallosphaera-like and Stygiolobus-like. Cultured archaea from CHS belonged to the genera Sulfolobus. The bacterial isolate belonged to a new species of Alicyclobacillus called Alicyclobacillus vulcanalis. A. vulcanalis has a temperature optima of 55°C, pH optima of 4.0, a %G+C content of 62 and possesses o-cyclohexyl fatty acids as the major lipid component. Sequencing of the merA gene of A. vulcanalis showed that merA shared the closest identity to the merA genes of other Bacillus spp. and Gram+ bacteria. Sequence comparison of the merA genes of the archaeal and bacterial isolates from CHS revealed that HGT of merA did not occur between the two domains at CHS. A merA gene profile of uncultured archaea at CHS showed that there was very little diversity in the merA genes from CHS. This result could mean the predominance of a particular archaeal species selected for by the high mercury concentration and the yearly cycle of dehydration and rehydration that CHS undergoes. The results of this study will contribute to our understanding of the microorganisms that participate in global mercury cycling and provide baseline information that can aid in the formulation of strategies for bioremediation and mercury recovery.