Effects of light on the performance of electricity-producing bacteria in a miniaturized microbial fuel cell array

Due to an increased concern about the global energy crisis and environmental pollution, microbial fuel cells (MFCs) have been a major focus for renewable energy production. To date, however, a surprisingly small number of bacterial strains and their optimal growth conditions have been investigated for use in MFCs, revealing a crucial lack of fundamental knowledge as to which bacteria species or consortia may be best suited for generating power in MFCs. This lack of knowledge is due to the fact that current screening methods are depending on larger scale two-bottle MFCs that require long start-up times, as well as the inability of conventional MFC arrays to generate electricity in a reliable, robust, and reproducible manner. In particular, the influence of light on the bacterial growth conditions and their power generation has not been fully reported because conventional MFC's opaque device/anode configuration leads to inefficient light penetration. This paper presents a miniaturized high-throughput parallel analyses platform not only for the screening/characterization of the electrochemical activities of electrogenic bacteria but also for investigation of the effect of light on bioelectricity generated from eight different microbial consortia in anode or cathode compartment; wild-type Shewanella oneidensis MR-1, Synechocystis sp. PCC 6803, wild-type Pseudomonas aeruginosa PAO1, and isogenic nirS, lasl, bdlA, and rpoS mutants, respectively. The array consists of nine MFC units with (i) transparent thin gold anode on PMMA layers for efficient light penetration and (ii) independent microfluidic accesses allowing for long term analysis ability without contamination from chamber to chamber during operation. Each MFC unit contains vertically stacked 57μl anode/cathode chambers separated by a proton exchange membrane. S. oneidensis displayed the highest current generation among all the consortia, 4-fold higher than that of wild-type P. aeruginosa PAO1. However, all the other mutants produced significantly low current outputs. Current production by Synechocystis sp. PCC 6803 demonstrated a positive response upon illumination and a subsequent decrease of output in the dark while other MFC units showed negligible light responses.