Mercury methylation by novel microorganisms from new environments

Area of Science:

• Environmental microbiology
• Biogeochemistry
• Molecular biology

Background:

• Microbial mercury methylation converts toxic mercury into the neurotoxin methylmercury.
• Understanding the distribution of mercury-methylating organisms is crucial for assessing environmental risk.
• The hgcAB gene cluster was recently identified as a potential marker for mercury methylation.

Purpose of the Study:

• To determine if the hgcAB gene cluster is a reliable predictor of mercury methylation capability in diverse microorganisms.
• To expand the known phylogenetic and environmental range of mercury-methylating organisms.

Main Methods:

• Screening microbial genomes for hgcAB orthologues.
• Culturing diverse bacterial and archaeal strains encoding hgcAB.
• Directly measuring methylmercury production in these strains.

Main Results:

• The presence of hgcAB orthologues reliably predicted mercury methylation capability across tested species.
• Mercury methylation was confirmed in species beyond sulfate- and iron-reducing bacteria, including methanogens and various Firmicutes.
• Novel environmental niches for mercury methylation were identified, such as rice paddies and animal guts.

Conclusions:

• The hgcAB gene cluster serves as a robust molecular marker for identifying mercury methylators.
• This discovery significantly broadens the known microbial players and habitats involved in methylmercury production.
• Linking methylation to discrete gene markers facilitates future environmental monitoring and risk assessment.