Metabolic changes in Klebsiella oxytoca in response to low oxidoreduction potential, as revealed by comparative proteomic profiling integrated with flux balance analysis.

Oxidoreduction potential (ORP) is an important physiological parameter for biochemical production in anaerobic or microaerobic processes. However, the effect of ORP on cellular physiology remains largely unknown, which hampers the design of engineering strategies targeting proteins associated with ORP response. Here we characterized the effect of altering ORP in a 1,3-propanediol producer, Klebsiella oxytoca, by comparative proteomic profiling combined with flux balance analysis. Decreasing the extracellular ORP from -150 to -240 mV retarded cell growth and enhanced 1,3-propanediol production. Comparative proteomic analysis identified 61 differentially expressed proteins, mainly involved in carbohydrate catabolism, cellular constituent biosynthesis, and reductive stress response. A hypothetical oxidoreductase (HOR) that catalyzes 1,3-propanediol production was markedly upregulated, while proteins involved in biomass precursor synthesis were downregulated. As revealed by subsequent flux balance analysis, low ORP induced a metabolic shift from glycerol oxidation to reduction and rebalancing of redox and energy metabolism. From the integrated protein expression profiles and flux distributions, we can construct a rational analytic framework that elucidates how (facultative) anaerobes respond to extracellular ORP changes.