Rapid Release of Arsenite from Roxarsone Bioreduction by Exoelectrogenic Bacteria

The extensive use of roxarsone in the poultry and livestock industry has led to increasing arsenic contamination of soil and aquatic environments. Microbial activity, especially exoelectrogenic bacterium (EEB)-mediated roxarsone bioreduction, plays important roles in such a bioconversion. However, the biomolecular-level mechanism behind this process and the reduction pathways remain largely unclear. Herein, the rapid anaerobic reduction of roxarsone by several EEB was explored, and the degradation pathways were clarified by using Shewanella putrefaciens CN32 as the model. The knockout of undA/mtrC led to a 70% loss of the roxarsone bioreduction ability within the initial 48 h. Both extracellular and intracellular reductions occurred simultaneously, resulting in the production of As(III) as the main inorganic arsenic species. Adding anthraquinone 2,6-disulfonate as a mediator considerably increased the roxarsone reduction rate by 119%. Given the wide distribution of EEB in environments, our findings facilitate a better understanding of the transformation behaviors of arsenic compounds in natural environments and highlight the necessity of re-evaluating the environmental risks of roxarsone.