Effect of Different Substrates on Growth and Redox Potential Kinetics of Escherichia coli Wild Type and Hydrogenases Lacking Mutant

Abstract

Escherichia coli is able to ferment different carbon sources and produce molecular hydrogen (H2) via four membrane-associated hydrogenase (Hyd) enzymes. The role of oxidation reduction potential (ORP) for bacterial metabolism and regulation of Hyd enzymes is stated. Moreover, relation of Hyds to F0F1-ATPase was also established during bacterial carbon source fermentation.The growth, ORP kinetics, proton-potassium exchange and the FoF1-ATPase activity of E. coli wild type BW25113 and Hyds lucking ΔhypF mutant were investigated upon different carbon sources utilization at pH 6.5 and 7.5. The essential role of Hyd enzymes for bacterial growth was shown upon glucose fermentation at both pHs: in mutant cells up to 2 times growth suppression was observed compared with wild type. Wild type ORP drop up to −400 −600 mV was observed upon glycerol, formate or glucose fermentation. Enhanced H2 production and 1.1- to 1.3-fold stimulation of bacterial growth were observed upon substrates co-supplementation. Whereas, during mutant growth ORP decrease only to −150 to 220 mV was observed upon glycerol or glucose fermentation at both pHs. Hyds participation in H+ extrusion was shown, but during glycerol fermentation their input is more than in glucose fermenting cells; moreover, during glucose fermentation depending of medium pH they have different relationship and role in potassium ions uptake and transport systems operation. During mixed carbon fermentation (glucose and glycerol) for the FoF1-ATPase activity of E. coli alkaline pH is more optimal. ATPase activity in ΔhypF mutant was suppressed at pH 7.5 which shows some interaction between Hyds components with FoF1.The results point out the significant role of substrates alone or their mixed combination and Hyd enzymes for E. coli growth, ORP formation and H2 production.