A conductive film produced by the supernatant from Serratia marcescens cultivation containing prodigiosin increases electricity generation in a microbial fuel cell

Abstract

Although Serratia marcescens is known for its natural ability to produce the red pigment prodigiosin, it has been little explored as a biocatalyst in bioelectrochemical systems (BES). Here, we have employed an environmental S. marcescens isolate S734 as biocatalyst in a microbial fuel cell (MFC) anode to oxidize glycerol and to produce energy; we have evaluated how the anode behaves in three conditions: (i) as an abiotic electrode (FC-A); (ii) as a biotic electrode after S. marcescens biofilm growth (MFC-B); and (iii) as an abiotic electrode added with the supernatant containing prodigiosin (FC-P). Scanning electron microscopy and electrochemical measurements indicated that prodigiosin formed a conductive film over FC-P, which increased charge transfer by 424 times compared to FC-A. The maximum power density during the FC-P operation was 10.0 mW/m⁻². Nevertheless, only in the presence of S. marcescens (MFC-B) was glycerol oxidized and electricity generated. Cyclic voltammetry indicated that the prodigiosin was the electrochemical active substance in the supernatant, and that its process was irreversible and controlled by adsorption. Electrochemical impedance spectroscopy confirmed that the prodigiosin-containing supernatant decreased the load resistance from 8396.3 Ω in FC-A to 58.10 Ω in FC-P. Genomic analysis showed that the prodigiosin biosynthesis gene cluster in strain S734 belonged to the Serratia 274 type, which contains pigA to pigN genes flanked by cueR and copA homologues. In conclusion, the supernatant produced by S. marcescens strain S734, containing prodigiosin could be explored as a green conductor in BES without further purification steps.