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Microbial methylation of metalloids: arsenic, antimony, and bismuth
Ronald Bentley1, Thomas G Chasteen
1Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA. rbentley@pitt.edu
Abstract:
A significant 19th century public health problem was that the inhabitants of many houses containing wallpaper decorated with green arsenical pigments experienced illness and death. The problem was caused by certain fungi that grew in the presence of inorganic arsenic to form a toxic, garlic-odored gas. The garlic odor was actually put to use in a very delicate microbiological test for arsenic. In 1933, the gas was shown to be trimethylarsine. It was not until 1971 that arsenic methylation by bacteria was demonstrated. Further research in biomethylation has been facilitated by the development of delicate techniques for the determination of arsenic species. As described in this review, many microorganisms (bacteria, fungi, and yeasts) and animals are now known to biomethylate arsenic, forming both volatile (e.g., methylarsines) and nonvolatile (e.g., methylarsonic acid and dimethylarsinic acid) compounds. The enzymatic mechanisms for this biomethylation are discussed. The microbial conversion of sodium arsenate to trimethylarsine proceeds by alternate reduction and methylation steps, with S-adenosylmethionine as the usual methyl donor. Thiols have important roles in the reductions. In anaerobic bacteria, methylcobalamin may be the donor. The other metalloid elements of the periodic table group 15, antimony and bismuth, also undergo biomethylation to some extent. Trimethylstibine formation by microorganisms is now well established, but this process apparently does not occur in animals. Formation of trimethylbismuth by microorganisms has been reported in a few cases. Microbial methylation plays important roles in the biogeochemical cycling of these metalloid elements and possibly in their detoxification. The wheel has come full circle, and public health considerations are again important.
Insights
Microorganisms and animals biomethylate arsenic, forming toxic gases and compounds. This process, crucial for biogeochemical cycling and detoxification, has public health implications, linking back to historical wallpaper poisoning incidents.
Area of Science:
- Environmental Chemistry
- Microbiology
- Toxicology
Background:
- 19th-century wallpaper poisoning linked to arsenical pigments and toxic gas production by fungi.
- Discovery of trimethylarsine (TMA) as the toxic gas and its use in arsenic detection.
- Demonstration of arsenic biomethylation by bacteria in 1971.
Purpose of the Study:
- To review the mechanisms and scope of arsenic biomethylation by various organisms.
- To discuss the enzymatic pathways involved in arsenic methylation.
- To explore the biomethylation of related metalloids like antimony and bismuth.
Main Methods:
- Review of scientific literature on arsenic biomethylation.
- Discussion of enzymatic mechanisms, including reduction and methylation steps.
- Analysis of techniques for determining arsenic species.
Main Results:
- Numerous microorganisms and animals biomethylate arsenic, producing volatile (methylarsines) and nonvolatile (methylarsonic acid, dimethylarsinic acid) compounds.
- Enzymatic mechanisms involve S-adenosylmethionine as a methyl donor and thiols in reduction.
- Biomethylation of antimony and bismuth by microorganisms is also established, with implications for biogeochemical cycling and detoxification.
Conclusions:
- Microbial methylation is a key process in the biogeochemical cycling and detoxification of arsenic, antimony, and bismuth.
- Understanding these pathways is crucial for addressing public health concerns related to metalloid exposure.
- Research continues to advance with improved techniques for arsenic species determination.