Carbon source utilization regulates biofilm formation and plant-beneficial interactions of Pseudomonas ogarae F113

Root exudate determines the gene expression of root associated bacteria, but the underlying mechanisms are poorly understood. We tested the hypothesis that carbon sources within root exudates regulate interactions of beneficial bacteria with the plant via carbon catabolite repression (CCR). Mutants in CCR genes were constructed in Pseudomonas ogarae F113, and rhizospheric traits were studied. P. ogarae F113 displays reverse CCR. The Δcrc mutant produced more biofilm than the wild-type strain, and its swimming was carbon source dependent. On roots, the bacterial expression of nirS, crcY, and crcZ was higher in the Δcrc mutant. Auxin expression (but not jasmonate signaling) in Arabidopsis thaliana was reduced upon inoculation by Δcrc or ΔcbrB mutants when compared with the wild-type strain. Our findings show that reverse CCR regulates the communication between P. ogarae F113 and A. thaliana, which sheds further light on the significance of root exudates for the functioning of plant-beneficial bacteria on roots.