Widespread microbial mercury methylation genes in the global ocean

Area of Science:

• Environmental microbiology
• Marine biogeochemistry
• Ecotoxicology

Background:

• Methylmercury is a potent neurotoxin biomagnifying in marine food webs.
• High methylmercury concentrations are found in oxic ocean waters, but the producers remain unidentified.
• Previous research implicated anaerobic microbes and suggested Nitrospina in Antarctic sea ice.

Purpose of the Study:

• To investigate the microorganisms responsible for methylmercury production in oxic seawater.
• To determine the prevalence and activity of mercury methylating genes in global oxic ocean waters.
• To identify the key microbial players in oceanic methylmercury cycling.

Main Methods:

• Metagenomic analysis to assess the genetic potential for mercury methylation.
• Metatranscriptomic analysis to evaluate gene expression levels.
• Bioinformatic analysis to identify microbial taxa and gene abundance.

Main Results:

• The genetic potential for methylmercury production (hgcAB genes) is widespread in oxic seawater globally.
• Nitrospina bacteria were identified as the predominant microorganisms carrying and expressing hgcAB.
• High hgcAB abundance and expression correlate with methylmercury concentrations in oxic subsurface waters.

Conclusions:

• Microbial methylmercury production is a significant process in oxic ocean waters.
• Nitrospina are identified as key methylators of mercury in the global ocean.
• Understanding these pathways is crucial for assessing risks posed by methylmercury to marine ecosystems and human health.