[Sheng, Yanqing] Chinese Acad Sci, Yantai Inst Coastal Zone Res, Key Lab Coastal Zone Environm Proc, Yantai 264003, Peoples R China

Photomicrobial fuel cells (pMFCs) are a new technology for transforming the light energy or bioenergy of algae into bioelectricity. However, the current methods of generating algal pMFCs have poor efficiency due to the complex electron transfer network in algal cells. In this study, pMFCs containing the model electricity-producing cyanobacterium Synechocystis sp. PCC6803 contaminated by additional bacteria exhibited a 12.6-fold greater voltage output compared to the control pMFCs with axenic Synechocystis sp. PCC6803. To explain this phenomenon, the compositions of symbiotic bacterial communities in bacterial-contaminated pMFCs were analyzed, and a pure strain WJ04 belonging to the genus Pseudomonas, which was the second most abundant (30.2%) among the total symbiotic bacteria, was obtained. The strain WJ04 was able to raise the voltage output by 8.3 fold compared with the control treatments, meaning that strain WJ04 contributed to the increased voltage output of pMFCs. Through the coculture experiment, strain WJ04 was found to influence the growth of Synechocystis, improve photosynthesis rates by regulating algal genes and further affect algal metabolite production compared with control treatments. In addition, nicotinamide, c-homocysteic acid and 4-aminobutyric acid (fold change analysis, F.C. >= 10) could regulate algal gene expression and enhance the coculture current density by 6.1-12.3 fold compared with the control treatments. Thus, these results provide a clear explanation for the high current production in bacterial-contaminated pMFCs, clarify the interaction mechanisms between algae and bacteria in the anode and provide accurate evidence for the role of bacteria in improving algal bioelectricity utilization.