Abstract
Escherichia coli cells rapidly respond to changes in the environment. Such response must be anticipated upon development of fermentation strategy for commercial purposes. The response may signal changes in cell physiology, which is critical for the cell growth and the level of the target protein production. One of the responses is the elevated expression of membrane proteins to tightly control the trafficking of molecules into and out from the cells. Normally, the expression level of the membrane protein is basal as the fermentation is carried out in physiological conditions. Here, we reported an elevated expression of the outer membrane protein A (OmpA) during a series of fermentation conduct, starting from the shake flask, 1-L to finally 10-L fermentor. The incidence led to a lower expression of the target protein and thereby resulting in lower process efficiency. OmpA expression was concomitant to the bacterial growth and already observed in the early exponential phase. Despite the drawback, this phenomenon actually inspires the observation of OmpA expression as one of the indicators for the E. coli cells response to the fermentation conditions. This auxiliary check would prevent the higher OmpA expression that led to the low expression of the target protein.