Genome-wide interrogation of genetic requirements for root colonization by CRISPRi-seq in Bacillus subtilis

Bacillus subtilis is a known plant growth promoting rhizobacterium, yet, the genetic basis of effective root colonization remains understudied. Here, we applied genome-wide CRISPR interference sequencing (CRISPRi-seq) to systematically identify genes required for early Arabidopsis thaliana root colonization by the B. subtilis strain 3610. Our genome-wide inducible CRISPRi library was used to screen for bacterial fitness during hydroponic root colonization. A complementary RNA-seq in the same conditions further revealed a distinct transcriptional state of root-associated cells. We identified 249 genes impacting root colonization. We reveal a critical role of cell envelope remodeling during early root association, specifically wall teichoic acid synthesis and D-alanylation. Moreover, we observed a metabolic shift toward TCA-cycle-driven aerobic growth with uptake of fructose, active repression of sporulation, competence and prophage programs, as well as induction of secondary metabolite biosynthesis. Our work establishes CRISPRi-seq as a powerful tool for dissecting bacterial-plant interactions relevant to sustainable agriculture.