Biotransformation of As, Cr, Hg, and Mn by Pseudomonadota: chances and risks

Heavy metals are among the key environmental contaminants which pose a threat to all the living organisms. Bacteria can help detoxify these elements by a range of mechanisms associated to bacterial metabolic processes. One of them is biotransformation, which consists in change in the oxidative state of an element, often followed by its absorption or precipitation. Pseudomonadota-a vast and diverse bacterial phylum-belong to the best studied microorganisms involved in the process. Our review shows their contribution to the redox-based detoxification of four trace elements: chromium, manganese, mercury, and arsenic. Based on a comprehensive literature survey, we try to assess the importance of individual orders and selected genera in redox transformations; we also identify potential risks associated with the use of Pseudomonadota in bioremediation and suggest the most promising directions for future studies and applications. The review leads to a conclusion that the potential of non-pathogenic rhizobia Hyphomicrobiales is particularly worth further exploration.