Use of oxidoreduction potential as an indicator to regulate 1,3-propanediol fermentation by Klebsiella pneumoniae

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Abstract
Anaerobic fermentation was relatively difficult to optimize due to lack of monitoring parameters. In this paper, a new method was reported using extracellular oxidoreduction potential (ORP) to monitor 1,3-propanediol (1,3-PD) biosynthesis process by Klebsiella pneumoniae. In batch fermentation, cell growth, 1,3-propanediol production and by-products distribution were studied at four different ORP levels: 10, −140, −190 and −240 mV. From the results, the ORP level of −190 mV was preferable, which resulted in fast cell growth and high 1,3-propanediol concentration. The NAD+/NADH ratio was determined at different ORP levels, and a critical NAD+/NADH ratio of 4 was defined to divide fermentation environments into two categories: relatively oxidative environment (NAD+/NADH>4) and relatively reductive environment (NAD+/NADH+/NADH, which determined metabolic flux. Furthermore, a batch fermentation of modulating ORP following a profile in different levels corresponding to different fermentation stage was tested. The 1,3-PD concentration was 22.3% higher than that of constant ORP fermentation at −190 mV. Therefore, ORP is a valuable parameter to monitor and control anaerobic fermentation production.