[Identification of a Facultative Bacterium Strain with the Ability to Methylate Mercury Under Both Aerobic and Anaerobic Conditions].

A strain with the ability to methylate mercury under both the aerobic and anaerobic conditions was isolated from soil of the water-level-fluctuation-zone in the Three Gorge Reservoir in Shibaozhai Village, Zhongxian Country, Chongqing, China (E108°12'3″ and N30°24'36″). The soil was classified as Purple soil with a pH of 7.97 (0-20 cm depth). The isolation was performed under 1.0 mg·L HgCl conditions. After its morphological and physiological characterization, and its phylogenetic analysis using 16S rDNA gene sequence, the strain was identified as sp., and named as XD-MeHg-B (GenBank accession number: KU954349). On one hand, at 30℃ under aerobic condition, the concentration of methylmercury (MeHg) in the PBS (phosphate buffer saline) solution, which was inoculated with 1×10 cfu·mL suspension of XD-MeHg-B and an initial Hg of 200 ng·L, was exponentially increased to 1.22 ng·L±0.15 ng·L after 60 min incubation and then approached to the maximum of 3.85 ng·L±0.33 ng·L 160 min after incubation. The largest mercury methylation rate was 1.93%. On the other hand, at 30℃ under anaerobic condition, the concentration of MeHg in the PBS solution, which was also inoculated with 1×10 cfu·mL suspension of XD-MeHg-B and an initial Hg of 200 ng·L, was 2.86 ng·L±0.73 ng·L and the largest mercury methylation rate was 1.43% 180 min after incubation. As a result, XD-MeHg-B showed its ability to methylate mercury under both aerobic and anaerobic conditions while with a comparatively hysteretic and lower ability of mercury methylation. These results demonstrated that XD-MeHg-B could be a promising candidate for further studies on mercury biogeochemical cycle, particularly under dry-wet alternative conditions.