A promotion strategy of enhancing the mercury removal in Shewanella oneidensis MR-1 based on the mercury absorption and electronic consumption via mer operon.

Shewanella oneidensis (S. oneidensis) bacteria have bioremediation capabilities for various heavy metals, however, their repertoire of mercury-removal proteins is limited, restricting their effectiveness in mercury remediation. In this study, the integration of an exogenous mer operon into S. oneidensis expanded the range of mercury-removal proteins, significantly boosting both mercury tolerance and removal efficiency. The engineering bacteria (MR-mer) exhibited growth in a 180 mg/L Hg²⁺ solution, showing a 40 % increase in tolerance over S. oneidensis. In a liquid medium with 50 mg/L Hg²⁺, the MR-mer strain achieved 73 % mercury removal efficiency, outperforming the original strain by 50 %, and facilitated Hg⁰ formation on the cell membrane. Extensive analysis of transmembrane structures and Fourier analysis revealed that mer operon proteins might target the cell membrane, modifying its functional group contents to enhance mercury adsorption. Additionally, the absence of the key protein OmcA in the electron transport chain led to a 30 % reduction in Hg²⁺ removal capacity. This suggests that S. oneidensis transfers electrons to the cell surface through this chain, providing electrons for Hg²⁺ reduction. In conclusion, the mer operon, targeting the cell membrane in MR-mer strain, synergizes with the electron transport chain to markedly elevate Hg²⁺ removal capability. This approach not only augments Shewanella 's mercury biodegradation capacity, but also offers novel perspectives for microbial heavy metal pollutant removal. [Display omitted] • Shewallena oneidensis achieved better removal rate to Hg²⁺ by expressing mer operon. • Mer operon expression aided the conversion of Hg²⁺ to Hg⁰ on the membrane. • The Mer operon utilizes bacteria extracellular electron to facilitate Hg²⁺ removal. [ABSTRACT FROM AUTHOR]