LysR family factor PltR positively regulates Pyoluteorin production in a pathway-specific manner in Pseudomonas sp M18

The pltR gene, coding a putative LysR-type regulator, was identified upstream Pit biosynthetic gene cluster in Pseudomonas sp. M18 using bioinformatics technology. The null mutation of p1tR resulted in mutant M18TRG (p1tR::Gm) by recombination and its Pit (Pyoluteorin) production declined to 30% while PCA (Phenazine-l-carboxylic acid) production remained unchanged as compared with the wild-type M18 grown in King's Medium B. After complementation, Pit production of mutant M18TRG was restored to the level in wild-type M18. Overexpression of p1tR in M18 led to 13-fold enhancement of Pit production over the wild-type M18 strain. However, PICA production was unchanged under this condition. These data suggested that PItR was a positive regulator on Pit production. Pit itself, however, could not regulate expression of p1tR. Expression of the pit-lacZ transcriptional fusion in mutant M18TRG declined obviously as compared with the wild-type M18, which further proved that PltR could regulate expression of Pit biosynthetic genes at the transcriptional level. In addition, the investigation on the p1tR expression in gacA mutant M18G and rsmA mutant M18R disclosed that PltR was involved in the positive regulation of gacA on Pit production while being excluded from the negative control caused by rsmA.