The role of glnR gene in heat and oxidative stress cross-adaptation in Lacticaseibacillus rhamnosus

Cross-adaptation is an interesting and valuable physiological phenomenon that occurs under complex stressful conditions. Lacticaseibacillus rhamnosus can cross-adapt to heat and oxidative stresses by decreasing transcription of nitrogen source transport and metabolism-related genes. In this study, the role of glnR, which is presumed to encode a global nitrogen regulator, was investigated using gene deletion. In the glnR mutant (glnRm), 305 genes were upregulated and 293 were downregulated under heat stress, whereas 156 genes were upregulated and 161 were upregulated under oxidative stress. Most of the nitrogen source metabolism-related genes downregulated by both heat and oxidative stresses in the wild-type strain were not responsive in the glnR mutant under the same conditions. After pretreatment with heat or oxidative stress, the heat and oxidative stress cross-adaptation of glnRm was weaker than that of the wild-type strain. Moreover, the glnR mutant showed poor survival during spray drying, and heat and oxidative pretreatments were no longer able to improve the survival rate. These findings indicated that L. rhamnosus glnR gene could respond to heat and oxidative stresses and connect tolerance to these two stresses, providing alternative research directions for improving the survival rate of L. rhamnosus during spray drying.