Biotransformation of metal(loid)s by intestinal microorganisms

Abstract

Many metals and metalloids undergo complex biotransformation processes by micro organisms in the environment, namely, Ge, As, Se, Cd, In, Sn, Sb, Te, Hg, Tl, Pb, Bi, and Po. Though the human intestine harbors a highly diverse and metabolically active microbial community, the knowledge on metal(loid) biotransformation by gut microbiota is limited. Microbial metal(loid) metabolism in the gut is highly relevant when assessing health risks from oral exposure, as both the bioavailability and the toxicity of the ingested compound can be modulated. This review gathers and compares a broad selection of scientific studies on the intestinal biotransformation of metal(loid)s.It can be inferred that metal(loid) biotransformation by intestinal microbiota is a common process, resulting in both beneficial and adverse toxicological effects. Whereas for Hg the intestinal demethylation of methylmercury results in enhanced elimination, highly bioavailable and toxic arsenic and Bi species are formed by intestinal microorganisms. In either case, we conclude that the gut microbial potency should be considered to be taken up in toxicokinetic studies and models for assessing the health risks of oral metal(loid) exposure. This will allow the relevance of intestinal metal(loid) biotransformation to be assessed for human health risks.

Controlled variation of redox conditions in a floodplain soil: Impact on metal mobilization and biomethylation of arsenic and antimony

“…decreased under oxidizing conditions. There are different studies about the methylation of As and Sb in the human body (e.g., Kojima et al, 2009;Diaz-Bone and Van der Wiele, 2010). In contrast to that, studies about methylation of As and Sb in soils are very scarce.…”

Arsenic induces structural and compositional colonic microbiome change and promotes host nitrogen and amino acid metabolism

“…There are also direct relationships between bacterial load, bacterial products (nitrogen metabolites and patern recognition ligands) in the systemic circulation, and inflammatory state of the liver and cardiovascular system (Wang et al , 2011; Corbitt et al , 2013; Tang and Hazen, 2014). In addtion, the intestinal microbiota is also involved in detoxification and biotransformation of toxic metals, modulation of host metabolic phenotypes, metabolism of otherwise indigestible dietary compounds and metabolism of xenobiotics that can have profound effect on host health (Diaz-Bone and Van de Wiele, 2010; Lundberg and Weitzberg, 2012). Thus identifying factors that impact the indigenous microbiota is key to understanding the dynamic interactions between the microbial community and health of the host.…”

Is gastrointestinal microbiota relevant for endogenous mercury methylation in terrestrial animals?

“…These species expand our known niches for MeHg production including anaerobic and methanogenic habitats such as the animal digestive tract and open new perspectives that should be further investigated. At this point, there are some previous ancient and recent works with different species (from invertebrates to humans) and experimental approaches where the methylation by gut bacteria was tested with contradictory results in some cases (DiazBone and Van de Wiele, 2010;Hill, 1995). Recently, Podar et al (2015) found that hcgAB was absent in the studied gastrointestinal microbiomes of mammals (datasets corresponding to humans, bovine, sheep, swine, mouse, dog, wallaby, giant panda and reindeer) and birds (datasets corresponding to broiler chicken and hoatzin), which suggests a low risk of endogenous MeHg production in terrestrial vertebrates.…”