Novel spectroscopy method to reveal optimal culture conditions in Escherichia coli fermenter.

Fermentation engineering is critical for mass-producing chemicals, food additives, and medicines, where optimal culture conditions maximize microbial growth and metabolite production. Although monitoring bacterial growth during fermentation is critical, there is a lack of a non-invasive and sensitive method to directly monitor the bacterial metabolism. In this paper, a novel optical monitoring method is proposed based on tunable diode laser absorption spectroscopy. First, the detecting system consisting of a laser, detection, a homemade board, and an incubator is established and verified to be able to monitor the metabolite production of CO2 in Escherichia coli through a 25-h detection period. Second, the quantitative growth rate analysis method is specified by calculating the threshold time (TT) intervals between consecutive dilution gradients, and the threshold with the least sum of residuals is chosen as the optimal threshold. Finally, alongside varied pH and temperature settings in a simulated fermenter, we elucidated the influence of these factors on E. coli metabolism curves and calculated the growth rates via TT, identifying 38°C as the optimal temperature and 7.0 as the optimal pH. This study presents a novel approach to reveal optimal culture conditions during fermentation holding promises for online real-time monitoring in the future.