Diversity of Mercury-Tolerant Microorganisms Original paper

What was reviewed?

This review summarized the diversity of mercury-tolerant microorganisms and explained how bacteria, fungi, and microalgae survive and transform mercury in contaminated environments. The authors connected mercury’s environmental forms (elemental, inorganic, and organic such as methylmercury) to microbial processes that either convert mercury into less toxic forms or, in some settings, generate the most toxic form through methylation. They framed these organisms as practical tools for bioremediation because microbes can bind mercury, accumulate it, chemically transform it, or reduce it to volatile elemental mercury.

Who was reviewed?

The authors reviewed research on environmental microorganisms rather than human patients. They covered microbes isolated from mercury-impacted soils, sediments, seawater, industrial and municipal waste streams, mining-affected ecosystems, and plant-associated niches such as rhizospheres. They highlighted findings from diverse microbial groups, including sulfate-reducing and iron-reducing bacteria linked to methylmercury formation, as well as bioaccumulating and volatilizing strains that can lower bioavailable mercury in water or soil.

What were the most important findings?

The review emphasized that mercury tolerance is widespread and multi-mechanistic, and it often depends on genetic detoxification systems plus broader stress defenses. A central “microbiome signature” is the mer operon and related genes that encode transport and detoxification functions, including mercury uptake and regulation, cleavage of carbon–mercury bonds in organomercurials, and reduction of Hg2+ to Hg0. Beyond mer genes, many organisms rely on extracellular polymeric substances and biofilms that bind mercury outside the cell, thiol-based buffering and antioxidant responses that limit oxidative damage, and sequestration or precipitation that immobilizes mercury. The authors also reinforced that methylation and demethylation capacities vary by physiology and environment, with oxygen-free, nutrient, and redox conditions shaping whether microbial communities increase methylmercury risk or push mercury toward less harmful forms.

What are the greatest implications of this review?

For clinicians tracking microbiome-relevant exposures, this review supports a clear translational point: mercury risk is not only about dose, but also about microbial community function, especially genes and pathways that control mercury speciation. Environments that enrich methylating groups can raise methylmercury formation potential, while environments dominated by detoxifying and binding organisms can reduce bioavailable mercury and shift exposure profiles downstream in food webs. For remediation and public health, the review argues that bioremediation can be more sustainable than many chemical methods, but it requires careful design because some microbial activities can inadvertently increase methylmercury under certain conditions. For a microbiome signatures database, the most useful entry is functional: enrichment of merA/merB-linked detoxification capacity, EPS/biofilm-mediated binding potential, and anaerobic methylation potential in sulfate- and iron-reducing guilds.