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-2 respectively, but it increased to 327 and 274 μA·cm-2 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.
Keywords: Biofilm formation; Buffer concentration; Electroactive microorganism; Electron mediator; Shewanella oneidensis MR-1; Transcriptome.
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