T6SS modulates expression and secretion of FliC in Citrobacter freundii

Objective To screen fuction of CF74 T6SS genomic island. Methods We constructed deletion mutant of T6SS genomic island, and used 2-DE to compare the proteins in the WCL and culture supernatants from bacteria grown to stationary phase in LB between the wild-type and CF74T6SS mutant. Results In WCL, 4 and 42 protein-coding genes exhibited higher or lower levels of expression in CF74T6SS, respectively. FliC was found to have markedly decreased production in CF74T6SS. In culture supernatants, we identified 27 up-regulated and 36 down-regulated proteins in CF74T6SS. Three flagellar proteins, FliC, FlgK and FliD were identified, which were expressed less in CF74T6SS. Conclusion The absence of T6SS reduced the production and secretion of FliC and at least 2 other flagellar proteins.