Exponential feeding for high yield production of Xylose Reductase (CtXR) in E. coli fed-batch fermentation

In order to find a Xylose Reductase (XR) with high activity at elevated temperatures, a research was carried out in the Institute of Chemical, Environmental and Bioscience Engineering from Austria, to characterize a novel recXR (isolated from Chaethomium thermophilum (Ct) and expressed on Escherichia coli). A LAMBDA PRECIFLOW peristaltic pump was used for the feed-forward controlled exponential feeding strategy performed to produce high amount of biomass and product CtXR in E. coli fed-batch fermentation. 

XR are enzymes which allow the utilization of hemicellulosic biomass for ethanol production in yeasts and as a biocatalyst to obtain xylitol for pharmaceutical and food industries.

Figure 1. An exponential feeding strategy was used for the high cell-density E. coli fed-batch fermentation. Xylose Reductase (CtXR, 360 U/L) got purified and characterized. Quehenberger, J.; Reichenbach,T.; Baumann, N.; Rettenbacher, L.; Divne, Ch; Spadiut, O. Kinetics and Predicted Structure of a Novel Xylose Reductase from Chaetomium thermophilum. International Journal of Molecular Sciences 20(1):185 · January 2019.

After 34 h total fermentation time, 230 g/L wet cell weight (corresponding to 62 g/L dry cell weight) were harvested. Crude extract derived from 230 g wet cell weight contained a total activity of 360 U, resulting in a titer of 360 U/L or 5.8 U/g dry cell weight.

Common feeding strategies for fed-batch fermentation processes

Fed-batch culture represents a semi-open fermentation process in which one or more nutrients are aseptically and gradually feeded to the fermentor while the fermentation broth with the culture and product is retained in the vessel.

Common feeding strategies for fed-batch fermentation include:

• Discontinuous feeding (by regular or irregular pulses of substrates).

• Regular continuous feeding designed according to a precalculated profile.

• Regular continuous feeding based on the feedback control of online measured variables associated with cell growth and metabolism.

Other feeding classifications:

• Constant feeding rate.

• Linearly increasing feeding rate.

• Exponential feeding rate.

• Modified exponential feeding rate.

• Control by a feed-forward feeding strategy.

Precise peristaltic pump for liquid feed in fed-batch fermentation

Any fed-batch fermentation with liquid feed, a highly precise and stable feed pump is greatly desired in order to achieve a refined and tune control of any feeding step, regardless whether the control follows a feedback strategy or a feed-forward strategy.

Figure 2. LAMBDA peristaltic pump is the precise feed pump for fed-batch fermentation.

LAMBDA peristaltic pumps were especially constructed for long-term fermentation:

The feed pump is programmable on its display and also used remote controlled by feed software PNet for constant, linear or exponential feeding profiles for (feed-forward strategy).

For feedback strategy, the LAMBDA peristaltic pump is connected to the fermentor and automation software SIAM. The software receives parameter actual values from the fermentor and remote controls the feed pump according the customized strategy. Thus, it allows for example to use the DO (dissolved oxygen) signal to remote control the exponential C-feed of the fed-batch fermentation.

More information about the precise feed pump series for fed-batch fermentation, you will find on www.lambda-instruments.com/peristaltic-pumps/.

Please, contact us at sales@lambda-instruments.com if you have questions, need quotation or prices of feed pumps.

Keywords: Fed-batch, feeding strategies, fermentation, feed pump, peristaltic pump, E. coli, Xylose reductase, LAMBDA PRECIFLOW, exponential feeding