LasR Might Act as an Intermediate in Overproduction of Phenazines in the Absence of RpoS in .

As an opportunistic bacterial pathogen, PAO1 contains two phenazineproducing gene operons, () and (), each of which is independently capable of encoding all enzymes for biosynthesizing phenazines, including phenazine-1-carboxylic acid and its derivatives. Other previous study reported that the RpoS-deficient mutant SS24 overproduced pyocyanin, a derivative of phenazine-1- carboxylic acid. However, it is not known how RpoS mediates the expression of two operons and regulates pyocyanin biosynthesis in detail. In this study, with deletion of the gene in the PAΔ mutant and the PAΔ mutant respectively, we demonstrated that RpoS exerted opposite regulatory roles on the expression of the and operons. We also confirmed that the operon played a critical role and especially biosynthesized much more phenazines than the operon when the gene was knocked out in . By constructing the translational reporter fusion vector - and the chromosomal fusion mutant PAΔ::, we verified that RpoS deficiency caused increased expression of , a transcription regulator gene in a first quorum sensing system () that activates overexpression of the operon, suggesting that in the absence of RpoS, LasR might act as an intermediate in overproduction of phenazine biosynthesis mediated by the operon in .