Physiological Function of AtrN in Regulating Intracellular NADPH Levels and the Anti-Reductive Stress Response in Corynebacterium glutamicum

The regulation of intracellular NADPH levels is currently a hotspot for research into bacterial modification and fermentation process optimization, and Corynebacterium glutamicum, an important industrial microorganism, achieves enhanced L-lysine production by regulating intracellular NADPH levels. In previous studies, transcriptome analysis was performed on C. glutamicum with different intracellular NADPH levels. The results showed that the expression level of transcription factor AtrN changed significantly. Moreover, experiments showed that transcription factor AtrN can sense high intracellular levels of NADPH and negatively regulate its synthesis. In this study, we integrated the pntAB gene of Escherichia coli into the genome of C. glutamicum XQ-5, successfully constructing a chassis cell with a high intracellular NADPH level. It was named TQ-1. On this basis, we knocked out and complemented the AtrN in strain TQ-1, resulting in strains TQ-2 and TQ-3, respectively. Then, the changes in cell growth, intracellular redox substances and cell membrane among these three strains were investigated. We found that the growth of TQ-2 was inhibited in the early growth stage and the cell survival rate was decreased because of the high increase in the intracellular NADPH level. In addition, the deletion of the AtrN gene also led to a decrease in the fluidity and an increase in the permeability of the cell membrane. Compared with TQ-1, TQ-3 showed slow growth only in the late growth stage, and the fluidity of its cell membrane was also enhanced. This indicates that AtrN guides the cells to make some adaptive changes to maintain cell growth when facing excessive intracellular reductive stress. This will facilitate future research on how potential upstream regulatory genes regulate AtrN and how AtrN regulates downstream genes to cope with cellular reductive stress. It also provides theoretical guidance for the specific modification of high-yield lysine-producing strains.