Identification of a Facultative Bacterium Strain with the Ability to Methylate Mercury Under Both Aerobic and Anaerobic Conditions
TAO Lan-lan;XIANG Yu-ping;WANG Ding-yong;HUANG Man-lin;SHEN Hong;College of Resources and Environment,Southwest University;Chongqing Engineering Research Center for Agricultural Non-point Source Pollution Control in the Three Gorges Region;
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. 0mg·L- 1Hg Cl2 conditions. After its morphological and physiological characterization,and its phylogenetic analysis using 16 S r DNA gene sequence,the strain was identified as Pseudomonas fluorescens sp.,and named as Pseudomonas fluorescens XD-Me Hg-B2( Gen Bank accession number: KU954349). On one hand,at 30℃ under aerobic condition,the concentration of methylmercury( Me Hg) in the PBS( phosphate buffer saline) solution,which was inoculated with 1 × 1011cfu·m L- 1suspension of P. fluorescens XDMe Hg-B2 and an initial Hg2 +of 200 ng·L- 1,was exponentially increased to 1. 22 ng·L- 1± 0. 15 ng·L- 1after 60 min incubation and then approached to the maximum of 3. 85 ng·L- 1± 0. 33 ng·L- 1160 min after incubation. The largest mercury methylation rate was1. 93%. On the other hand,at 30℃ under anaerobic condition,the concentration of Me Hg in the PBS solution,which was also inoculated with 1 × 1011cfu·m L- 1suspension of P. fluorescens XD-Me Hg-B2 and an initial Hg2 +of 200 ng·L- 1,was 2. 86 ng·L- 1±0. 73 ng·L- 1and the largest mercury methylation rate was 1. 43% 180 min after incubation. As a result,P. fluorescens XD-Me Hg-B2 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 P. fluorescens XD-Me Hg-B2 could be a promising candidate for further studies on mercury biogeochemical cycle,particularly under dry-wet alternative conditions.