Distinct biofilm formation regulated by different culture media: Implications to electricity generation.

Biofilm of Shewanella oneidensis MR-1 is extensively studied as it can transform organic compounds directly into electricity. Although revealing the biofilm regulation mechanism is crucial for enhancing bio-current, studies regarding the mechanism by which the culture condition affects biofilm formation are still lacking. The biofilm formation of S. oneidensis MR-1 in two typical media with same electron donor was investigated in this study. Bio-electricity increased 1.8 times in medium with phosphate-buffered saline (PBS) than in piperazine-1,4-bisethanesulfonic acid (PIPES). Biofilm total protein has 1.5-fold of difference between two media at day 3, and biofilm structures also differed; a fluffy biofilm with curled cells was formed in medium with PBS, whereas a compact, ordered, and closely attached biofilm was formed in medium with PIPES. Transcriptome studies clarified that the expression of genes beneficial for cell aggregation [e.g., aggA (2.3 fold), bpfA (2.8 fold) and csgB (3.9 fold)] in medium with PIPES was significantly upregulated, thus provided an explanation for the specific biofilm structure. Buffer concentration was proved to be a critical factor impacted cell morphology and current generation. The maximum current density in 30 mM of PBS and PIPES is 165 and 159 μA·cm respectively, but it increased to 327 and 274 μA·cm in 200 mM of PBS and PIPES. This study provides new insights into the mechanism of medium-dependent biofilm regulation, which will be beneficial for developing simple and efficient strategies to enhance bio-electricity generation.