Biotransformation of mercury by bacteria isolated from a river collecting cinnabar mine waters

Abstract

One hundred six strains of aerobic bacteria were isolated from the Fiora River which drains an area of cinnabar deposits in southern Tuscany, Italy. Thirty-seven of the strains grew on an agar medium containing 10μg/ml Hg (as HgCl2) with all of these strains producing elemental mercury. Seven of the 37 strains also degraded methylmercury. None of 106 sensitive and resistant strains produced detectable monomethylmercury although 15 strains produced a benzene-soluble mercury species. Two strains of alkylmercury (methyl-, ethyl- and phenylmercury) degrading bacteria were tested for the ability to degrade several other analogous organometals and organic compounds, but no activity was detected toward these compounds. Mercury methylation is not a mechanism of Hg resistance in aerobic bacteria from this environment. Growth of bacteria on the agar medium containing 10μg/ml HgCl2 was diagnostic for Hg detoxification based on reduction.

Mercury exposure and its effects on fertility and pregnancy outcome

“…Contamination of the biosphere by Hg is mainly caused by anthropogenic factors, including coal combustion, mining, cement production and chemical industry . When Hg is released into the natural environment, and in groundwater, microorganisms including bacteria are often responsible for the biotransformation of the metal leading to the formation of methylmercury (MeHg) . Methylmercury and ethylmercury (EtHg) are highly hazardous forms that accumulate in freshwaters, ecosystems and food chains, leading to Hg exposure in people and other natural living organisms .…”

“…[3][4][5] When Hg is released into the natural environment, and in groundwater, microorganisms including bacteria are often responsible for the biotransformation of the metal leading to the formation of methylmercury (MeHg). 6,7 Methylmercury and ethylmercury (EtHg) are highly hazardous forms that accumulate in freshwaters, ecosystems and food chains, leading to Hg exposure in people and other natural living organisms. [8][9][10] Worldwide, global recognition of the great concern caused by Hg pollution led to the adoption of the Minamata Convention on Mercury in 2017.…”

Detection of the merA gene and its expression in the environment

“…Bacteria mediate three primary transformations of mercury: (1) the reduction of mercury, (2) the methylation of mercury, and (3) the demethylation of methyl mercury [10]. Mercury-resistant bacteria have been isolated from water [1], sediment [30], soil [39] and clinical sources [23]. They appear to be ubiquitous in the environment and may account for 1-10% of the heterotrophic bacteria in noncontaminated sites and as many as 50% of the bacteria from contaminated sites [4].…”

Distribution of DNA Sequences Encoding Narrow- and Broad-Spectrum Mercury Resistance

“…Of 1,300 gram-negative bacteria isolated from hospitals, rural humans, and farm animals, 14.3% had narrow-spectrum mercury resistance compared with 1.4% which exhibited broad-spectrum mercury resistance (11). In a study of bacteria isolated from a river draining an area of cinnabar deposits, 35% were resistant to HgCl2 and 6.6% degraded methylmercury (1).…”