Interdependence of Escherichia coli formate dehydrogenase and hydrogen-producing hydrogenases during mixed carbon sources fermentation at different pHs

The role of Escherichia coli FhlA transcriptional activator in generation of proton motive force and FOF1‐ATPase activity at pH 7.5

“…Carbon Conversion Efficiency (CCE) was determined by the following formula: CCE = C 2 *100%/C 1 , where C 1 is the concentration of carbons in the substrates (mM) during the given period, C 2 is the concentration of carbons in the fermentation end product (mM) during the same period of growth. 4,27 The substrate utilization rate was calculated as difference of decreasing concentration of substrate per hour, and end-product generation rate was determined as difference of increasing concentration of product per hour and expressed in mmol hr −1.4,27…”

“…The bacterial growth was monitored measuring the optical density OD 600 spectrophotometrically (UV–VIS spectrophotometer, Cary 60, Agilent Technologies, USA). Specific growth rate (μ) was determined by regular measurement of optical density (OD) until the stationary phase with doubling time as described before 4,8,27 . DCCD with 0.2 mM final concentration was used as indicated.…”

“…Specific growth rate (μ) was determined by regular measurement of optical density (OD) until the stationary phase with doubling time as described before. 4,8,27 DCCD with 0.2 mM final concentration was used as indicated.…”

“…In this context, previously it has been shown higher Hyd and FDH-H specific activities at 72 hr, compared to 24 hr during mixed carbon fermentation, which is another evidence for accelerated metabolism at 72 hr. 27 In fhlA mutant glycerol remained as carbon substrate at 72 hr, which utilization rate and thus weak acids generation was lower (see Figure 2b). Under these conditions, the translocation of protons suggested was quite limited, which is shown by ΔpH value at 72 hr.…”

“…It is promoted by the high activity of the FDH-H enzyme, which catalyzes the oxidation of synthesized formate as a weak acid. 27 Moreover, it is known that ethanol synthesis is accompanied by NADH + H + oxidation, which also contribute to pH in alkalization. In fhlA mutant the pH in alkalization is relatively low, compared with wt, which is explained by formate accumulation and lack of the ability for its neutralization.…”