Pseudomonas chlororaphis HT66 is a significant growth-promoting rhizobacteriaum in plants.It is reportedly the highest phenazine-1-carboxamide(PCN)producing wild type microbe studied thus far. Based on the whole-genome sequence analysis, we find that two genes phzⅠ and phzR are located just upstream of the phenazine biosynthesis gene cluster.Plate assays with Chromobacterium violaceum CV026 and Agrobacterium tumefaciens NTL4 were used to analyze the signals of strain HT66.With the addition of the fermentation broth extracts, strain NTL4 produced blue pigment, but the CV026 did not produce purple pigment.Then, using a gene knock-out method, we constructed ΔphzⅠ and ΔphzR HT66 mutants.The results show that both the ΔphzⅠ and ΔphzR mutants are unable to produce PCN.And the plate assay of ΔphzⅠ culture extracts shows no blue pigment is produced by strain NTL4.It suggests that phenazine biosynthesis is regulated by the quorum sensing system and AHL signals in strain HT66.Additionally, the ΔphzⅠ and ΔphzR mutants have some changes in the morphology of colonies and antifungal activity in vitro.Moreover, compared with wild type, the swimming motility of ΔphzⅠ mutant decreases greatly, while the swarming motility has no significant change.
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