Analysis of the “NADH pathway” in whole cells of Enterobacter aerogenes for H2 production and its new application in NAD+ regeneration

  • Chong Zhang, Department of Chemical Engineering, Tsinghua Univerisity, China
  • Kun Ma, Institute of Biochemical Engineering, Department of Chemical Engineering, Tsinghua University, Tsinghua Yuan, Beijing, China
  • Xin-Hui Xing, Institute of Biochemical Engineering, Department of Chemical Engineering, Tsinghua University, Tsinghua Yuan, Beijing, China

    • The mechanism of the “NADH pathway” for H2 production in whole cells of Enterobacter aerogenes was studied. Externally added NADH was proved to be oxidized by E. aerogenes to form 1 mol of H2 and NAD+, and the formed NAD+ was then utilized by the cells to produce H2. NADH was transformed to NAD+ by E. aerogenes cells, and at the same time, the intracellular protons were reduced. Under anaerobic conditions, the reduced protons was seemed to be supplied to a membrane bound, putatively NADH-linked [NiFe] hydrogenase. This hydrogenase was responsible for the formation of H2 via the NADH pathway. While under aerobic condition, the reduced protons were reacted directly with oxygen to form H2O via the electron transport chains in the cells. By coupling the NADH oxidization in whole cells with an NAD+-dependent ADH, a new NAD+ regeneration system was constructed, reaching a total turnover number (TTN) of 580 for the oxidization of ethanol to aldehyde.