The methylation of mercuric chloride by human intestinal bacteria

Area of Science:

• Microbiology
• Environmental Science
• Toxicology

Background:

• Methylmercury is a potent neurotoxin with significant environmental and health implications.
• Microbial methylation of inorganic mercury is a key process in the environmental mercury cycle.
• Understanding microbial mercury metabolism is crucial for assessing risks associated with mercury contamination.

Purpose of the Study:

• To investigate the capacity of various human gut bacteria to synthesize methylmercury compounds.
• To compare the methylmercury synthesizing abilities of aerobic and anaerobic bacteria found in human feces.

Main Methods:

• Isolation and culturing of bacterial strains (Staphylococci, Streptococci, Yeasts, E. coli, and obligate anaerobes) from human fecal samples.
• Incubation of bacterial cultures with mercuric chloride (HgCl2) under controlled conditions.
• Quantification of methylmercury production using appropriate analytical techniques.

Main Results:

• Most tested strains of Staphylococci, Streptococci, Yeasts, and Escherichia coli (E. coli) demonstrated the ability to synthesize methylmercury.
• In contrast, only a few strains of obligate anaerobic bacteria isolated from human feces could synthesize methylmercury.
• Significant methylmercury formation (up to 6 ng/ml) was observed within 44 hours from a low concentration of mercuric chloride (2 µg/ml).

Conclusions:

• Aerobic and facultative anaerobic bacteria commonly found in the human gut are significant producers of methylmercury.
• The limited methylmercury synthesis by obligate anaerobes suggests a differential role of gut microbiota in mercury methylation.
• These findings highlight the potential contribution of human gut microbiota to methylmercury production and its subsequent environmental fate.