Transcriptomic analysis of Bacillus licheniformis 2709 reveals the molecular mechanism of alkaline protease biosynthesis regulated by the DegS/DegU two-component system.

The DegS/DegU two-component signal transduction system (TCS), plays significant roles in a broad range of bacterial responses to the complicated environment in Bacillus subtilis. However, few efforts have been made to explore the physiological functions of DegS/DegU in alkaline protease (AprE) biosynthesis in the industrial strain Bacillus licheniformis 2709. In this study, it was found that the biosynthesis of AprE is severely hampered in degS and degU deficient mutants compared with the original strain. To investigate the underlying mechanisms responsible for changing the AprE productivity, transcriptome profile analysis was conducted to compare the differentially expressed genes (DEGs) among the deficient mutants and the control. At the peak of AprE production in degS mutant, a total of 810 DEGs including 125 up-regulated and 685 down-regulated were identified compared to the control, which were mainly annotated in 15 pathways, including oxidative phosphorylation, amino acid metabolism and ABC transporters. Besides, the transcriptomic analysis of degU mutant revealed that 307 genes were significantly up-regulated and 604 genes were down-regulated, among which, rho was identified and further functionally verified. Systematic comparison of DEGs under different conditions elucidated self-repression mechanism of DegU on aprE expression in B. licheniformis 2709, which was confirmed by the inducible expression of degU::gfp in this study. The study will yield valuable insight into how the DegS/DegU TCS regulates aprE expression in industrial strain with respect to protease production, and facilitates genetic strain improvement aiming at biological containment and effectiveness of biotechnological processes.