Synthesized effects of proteomic and extracellular polymeric substance (EPS) revealing the enhanced hydrogen production by formed biofilm of photo-fermentative bacteria

Photo-fermentative hydrogen production, the new energy production alternative, was greatly enhanced by formed biofilm. To understand the mechanism of enhancement, the intracellular proteome and extracellular polymeric substance (EPS)ii EPS: extracellular polymeric substanceiiPFHP: Photo-fermentative hydrogen productioniiiPFB: photo-fermentative bacteriaivQS: quorum sensingvCLSM: Confocal laser scanning microscopyviCR: Control reactorviiBR: Biofilm reactorviiiTEM: Transmission electron microscopeixXPS: X-ray photoelectron spectroscopyxFTIR: Fourier transform infrared spectroscopyxiSM: Supplementary materialsxiiDEPs: Differentially expressed proteinsxiiiTCA cycle: Tricarboxylic acid cyclexivGO: Gene ontologyxvKEGG: Kyoto encyclopedia of genes and genomes during biofilm formation were investigated in this work. Experimental results indicated that a possible and effective altered system could transfer light to hydrogen. Proteins were significantly regulated, for example those related with nitrogenase, flagellin, EPS transportation and DNA duplication were up-regulated while those concerned photosystem were down-regulated. It revealed these changes of proteins contributed to positive activity of key enzymes, improved communication system and increased total light utilization efficiency thus leading to enhanced capacity of hydrogen production. Besides above metabolic changes inside the cells, EPS secreted by the bacteria played an important role in hydrogen production and its yield decided the release of hydrogen. When EPS descended to a lower concentration during biofilm formation, it meant carbon source for EPS synthesis was reduced, and more energy and reducing power could be transferred into hydrogen energy. More importantly, this work found that composition and structure of EPS were efficiently influenced by the formation of biofilm, such as benzene and O-H structure, secondary protein structure and the kinds of protein, which were important to stable biofilm and efficient hydrogen production. Therefore, final hydrogen yield was improved by altered protein and EPS resulted from biofilm formation. This study demonstrated that formation of biofilm is an efficient, ecological and attracting way to the future bio-hydrogen production.