Microbial Methylation of Metalloids: Arsenic, Antimony, and Bismuth

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

Genomic sequence of the pathogenic and allergenic filamentous fungus Aspergillus fumigatus

“…Elsewhere in the A. fumigatus genome, genes for an arsenite efflux pump and an arsenite translocating ATPase as well as additional copies of the arsenate exporter and arsenic resistance genes have been identified (Supplementary Table S9). This gene complement supports the classification of A. fumigatus among the once notorious 'arsenic fungi', organisms that produce the volatile trimethylarsine when grown in arsenate-contaminated environments 27 .…”

Treatment of groundwater containing Mn(II), Fe(II), As(III) and Sb(III) by bioaugmented quartz-sand filters

“…Both enter the aquatic ecosystem from natural and anthropogenic sources and can threaten water quality (Guo et al, 2009;Smedley and Kinniburgh, 2002). Furthermore, given their positions on the periodic table, As and Sb have similar chemical and toxicological properties (Bentley and Chasteen, 2002), with their trivalent species exhibiting greater toxicological effects than that of their pentavalent species (Gebel, 1997). Due to the high toxicities of As and Sb, the drinking water standards suggested by the World Health Organazation (2011) are set at 10 mg/l (As) and 5 mg/l (Sb).…”

Natural wetland emissions of methylated trace elements

“…4a) can hardly induce specific Se volatilizing enzymes for detoxification, which is often presumed to be the main driver for methylation of Se 37 . Furthermore, the higher volatilization efficiency of Se over As may be caused by the fewer required intermediates in the methylation process of Se compared with As 13,15 , which concurrently may explain the abundance of non-volatile, methylated As in the surface water.…”

“…Similarly to Se, arsenic (As) is a trace element irregularly distributed in soils and groundwater, and elevated levels of inorganic As in groundwater in Southeast Asia, for example, have resulted in serious human health problems 14 . Similar to Se and S, As also forms organic, methylated species in nature 15,16 . Methylation and subsequent volatilization of As have been quantified in laboratory experiments (for example, incubation studies with contaminated soils 17 ) but rarely in natural environments 18,19 .…”