Decoding the pathways of arsenic biotransformation in bacteria

Arsenic (As), a heavy metalloid, occupies the topmost position in the list of the top ten hazardous chemicals published by the World Health Organization. The contamination of arsenic in groundwater predominantly utilized for irrigation and drinking is responsible for serious public health issues across the globe. The two most common arsenic species, i.e., inorganic arsenate and arsenite, are toxic and environmental pollutants. The toxicity of arsenic and its speciation are impacted by bacterial biotransformations. Bacteria have evolved several systems to deal with arsenic toxicity in their vicinity through detoxification and metabolism. The knowledge about these processes provides insight into the strategies employed by bacteria for arsenic biotransformation. In this study, we comprehensively discuss the genetics and molecular mechanisms of arsenate reduction, arsenite oxidation, methylation/demethylation, and other arsenic biotransformations. Relatively recent scientific discoveries and the use of molecular approaches have notably enhanced our understanding of these microbial processes present in the environment. The present review intends to focus on the diverse categories of arsenic-transforming and -metabolizing bacterial species and their genetics, recent advances in the mechanisms of the microbe-mediated As-biotransformation pathways, and their implications on the biogeochemical cycling of arsenic in nature. This review will further help to develop a better understanding of bacterial response to arsenic, bioremediation strategies, and future research fields.