Mechanisms of Extracellular Electron Transfer in Deep-sea Shewanella piezotolerans WP3 Under High Salinity Stress

Microorganism-mineral interaction is crucial to understand the degradation of organic matter in marine sediments involved in the electron exchange. Widespread metal-reducing bacteria Shewanella spp. has unique ability of extracellular electron transfer (EET), but it remains sparely explored about the EET activity and mechanism under high-salinity stress in the deep sea. Here, we studied the EET process and the underlying mechanism of Shewanella piezotolerans WP3 isolated from deep-sea (1914m). S. piezotolerans WP3 had comparable electroactivity to typical S. oneidensis MR-1, with the maximum current density of 9.7uA/cm2 achieved at 0.6 V vs. Ag/AgCl. Multiheme-cytochrome OmcA-MtrCAB complex and redox shuttle riboflavin jointly contributed to the EET. To reveal the extracellular electron transfer (EET) mechanism, we connected WP3 to Three-electrode single-chamber reactors for incubation and applied 0.6 Vvs. AgCl/Ag, and chose three treatments for transcriptome sequencing, with three replicate samples set up for each treatment, including the initial phase (0 hours), 0.6 V (7.1 hours after reactor start-up) and open circuit control.Transcriptome analysis indicated that redundant omcA genes with low expression may not function and riboflavin was preferentially converted from guanosine triphosphate under high-salinity conditions. Our findings give insights into the EET mechanisms of marine Shewanella, which is conducive to the treatment of high-salinity wastewater.