Dissimilatory metal reducing bacteria (DMRB) are capable of extracellular electron transfer (EET) to insoluble metal oxides, which are used as external electron acceptors by DMRB for their anaerobic respiration. The EET process has important contribution to environmental remediation mineral cycling, and bioelectrochemical systems. However, the low EET efficiency remains to be one of the major bottlenecks for its practical applications for pollutant degradation. In this work, Shewanella oneidensis MR-1, a model DMRB, was used to examine the feasibility of enhancing the EET and its biodegradation capacity through genetic engineering. A flavin biosynthesis gene cluster ribD-ribC-ribBA-ribE and metal-reducing conduit biosynthesis gene cluster mtrC-mtrA-mtrB were coexpressed in S. oneidensis MR-1. Compared to the control strain, the engineered strain was found to exhibit an improved EET capacity in microbial fuel cells and potentiostat-controlled electrochemical cells, with an increase in maximum current density by approximate 110% and 87%, respectively. The electrochemical impedance spectroscopy (EIS) analysis showed that the current increase correlated with the lower interfacial charge-transfer resistance of the engineered strain. Meanwhile, a three times more rapid removal rate of methyl orange by the engineered strain confirmed the improvement of its EET and biodegradation ability. Our results demonstrate that coupling of improved synthesis of mediators and metal-reducing conduits could be an efficient strategy to enhance EET in S. oneidensis MR-1, which is essential to the applications of DMRB for environmental remediation, wastewater treatment, and bioenergy recovery from wastes.

No abstract

No abstract

No abstract

No abstract

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.

No abstract

No abstract