Sulfate-reducing bacteria and sulfur-oxidizing bacteria interactions at redox interfaces: Implications for mercury...

Area of Science:

• Environmental Microbiology
• Biogeochemistry
• Mercury Contamination

Background:

• Methylmercury (MeHg) is a potent neurotoxin and bioaccumulative pollutant, posing risks to ecosystems and human health.
• MeHg production is highest at aquatic redox interfaces, driven by sulfate-reducing bacteria (SRB) and active sulfur cycling.
• Interactions between SRB and sulfur-oxidizing bacteria (SOB) are key to understanding MeHg production dynamics.

Purpose of the Study:

• To review mechanisms enhancing mercury (Hg) methylation at redox interfaces.
• To explore the roles of sulfur cycling, syntrophy, and microbial interactions in MeHg production.
• To identify knowledge gaps regarding SOB-Hg interactions and their impact on MeHg bioavailability.

Main Methods:

• Literature review focusing on Hg(II) methylation, inorganic sulfur cycling, and SRB-SOB interactions.
• Analysis of proposed mechanisms for enhanced Hg(II) methylation at redox interfaces.
• Identification of areas requiring future research, including direct evidence of SOB influence on Hg speciation.

Main Results:

• SOB may increase Hg(II) bioavailability by oxidizing SRB-produced sulfide, preventing HgS precipitation.
• SOB sustain SRB activity by generating sulfate, thereby promoting MeHg production.
• Direct evidence linking SOB activity to Hg speciation and MeHg production remains limited.

Conclusions:

• SRB-SOB interactions significantly influence MeHg production at aquatic redox interfaces.
• Understanding these microbial synergies is critical for predicting and mitigating MeHg risks.
• Further research is needed on SOB's direct role in Hg transformation and the impact of microbial metabolites.