1Simultaneous Cu(II) reduction (6.42 ± 0.02 mg/L/h), acetate production (1.13 ± 0.02 mg/L/h) from 2 inorganic carbon (i.e., CO 2 sequestration), and hydrogen evolution (0.0315 ± 0.0005 m 3 /m 3 /d) were 3 achieved in a Serratia marcescens Q1 catalyzed microbial electrosynthesis system (MES). The 4 biofilms released increasing amounts of extracellular polymeric substances (EPS) with a higher 5 compositional diversity and stronger Cu(II) complexation, compared to the plankton cells, at higher 6 Cu(II) concentrations (up to 80 mg/L) and circuital currents (cathodic potential of -900 mV vs. 7 standard hydrogen electrode (SHE)). Moreover, the biofilms reduced Cu(II) to Cu(0) more 8 effectively than the plankton cells. At Cu(II) concentrations below 80 mg/L, the dehydrogenase 9 activity in the biofilms was higher than in the plankton cells, and increased with circuital current, 10 which was converse to the lower activities of catalase (CAT), superoxide dismutase (SOD) and 11 antioxidative glutathione (GSH) in the biofilms than the plankton cells, although all these 12 physiological activities were positively correlated with the concentration of Cu(II). This is the first 13 study that evaluates the EPS constituents and the physiological activities of the biofilms and the 14 plankton cells in the MESs, that favors the production of acetate from CO 2 sequestration and the 15 simultaneous reduction of Cu(II) from organics-barren waters contaminated with heavy metals. 16 17 Keywords: microbial electrosynthesis system; Cu-tolerant biofilm and plankton cell; CO 2 fixation; 18 extracellular polymeric substances; physiological activity; variable cathode potential 19 20 21 22 23 24 *Revised manuscript with changes marked Click here to view linked References) in the cathodes and acetate in the anodes (Huang et al., 2015; 2018; Chen et al., 31 2016). Among the variety of heavy metals that can be recovered using microbial 32 electro-metallurgical processes, the recovery of Cu(II) has attracted significant attention due to its 33 frequent occurrence in acid mine drainage wastewaters (Ter Heijne et al., 2010;Zhang et al., 2015; 34 Wu et al., 2016; Kiran et al., 2018). Likewise abiotic cathodes, biocathodes utilizing 35 electrochemically active bacteria (EAB) have been shown to reduce Cu(II) to metallic Cu(0) and thus 36 remove the heavy metal from the catholyte solution (Huang et al., 2015; 2018; Shen et al., 2017; Tao 37 et al., 2017). 38 From another perspective, microbial electrosynthesis systems (MESs) are also emerging as 39 potential systems for the synthesis of valuable products from waste streams. One notable example is 40 the production of acetate from inorganic carbon such as bicarbonate, where the production rate of 41 acetate is modulated artificially by the application of an electrical current that interferes with the 42 microbial metabolism (Bajracharya et al., 2015; Venkata Mohan et al., 2016; Rojas et al., 2018). 43 Therefore, the combination of microbial electro-metallurgical processes of ...
