Inactivation of CbrAB two-component system hampers root colonization in rhizospheric strain of Pseudomonas aeruginosa PGPR2

Two-component systems (TCS) are one of the signal transduction mechanisms, which sense physiological/biological restraints and respond to changing environmental conditions by regulating the gene expression. Previously, by employing a forward genetic screen (INSeq), we identified that cbrA gene is essential for the fitness of Pseudomonas aeruginosa PGPR2 during root colonization. Here, we report the functional characterization of cbrAB TCS in PGPR2 during root colonization. We constructed insertion mutants in cbrA and its cognate response regulator cbrB. Genetic characterization revealed drastic down-regultion of sRNA crcZ gene in both mutant strains which play a critical role in carbon catabolite repression (CCR). The mutant strains displayed 10-fold decreased root colonization efficiency when compared to the wild-type strain. On the other hand, mutant strains formed higher biofilm on the abiotic surface, and the expression of pelB and pslA genes involved in biofilm matrix formation was up-regulated. In contrast, the expression of algD, responsible for alginate production, and its associated sigma factor algU was significantly down-regulated in mutant strains. We further analyzed the transcript levels of rsmA, controlled by the algU sigma factor, and found that the expression of rsmA was hampered in both mutants. The ability of mutant strains to swim and swarm was significantly hindered. Also, the expression of genes associated with type III secretion system (T3SS) was dysregulated in mutant strains. Taken together, regulation of gene expression by CbrAB TCS is intricate, and we confirm its role beyond carbon and nitrogen assimilation. •The two component systems (TCS) orchestrate an intricate network of regulatory pathways in response to external stimuli.•Earlier, we identified that cbrA gene was essential for the fitness of Pseudomonas aeruginosa PGPR2 during root colonization.•In this study, we have functionally characterized the role of cbrA and cbrB mutant strains in PGPR2 during root colonization.•The mutant strains displayed poor root colonization ability when compared to wild type strain.•The mutant strains displayed dysregulation of genes implicated with nutrient assimilation, motility, biofilm formation and T3SS.•Our results provide evidence for the differential regulation of gene expression by this global signal transduction system.•Understanding these signalling mechanisms would provide novel insights into plant-microbe interactions.