In vivo NMR system for evaluating oxygen-dependent metabolic status in microbial culture

To optimize an appropriate microbial culture in a fermentor, precise control of the medium's dissolved oxygen tension (DOT) is crucial. In particular, to study the effect of DOT on cellular metabolic status by using in vivo nuclear magnetic resonance (NMR) measurements, the set-up of the experiment must be optimized to maintain DOT in the culture. In the conventional method, DOT is monitored by a sensor inside a fermentor and is controlled by changing the agitation rate. Here, we report a novel and accurate system that minimizes time lag by an automated aeration flow control device, allowing an NMR spectrometer to monitor representative metabolites in real-time. To fulfill these two objects, the fermentor was composed of a fermentation vessel and two outer tubes, through which the medium was circulated by rotary pumps. One tube monitored DOT in via a sensor, and at the same time the other tube monitored metabolites via an NMR spectrometer. In this study, we used this system to analyze the responses of Escherichia coli cells under various oxygen conditions. The results validated the use of this system in the study of microbial metabolism.