[Regulation of GacA on two phz gene clusters and quorum sensing in Pseudomonas sp. M18]

The regulatory function investigation of two component system gacS/gacA on two phz gene clusters expression and quorum sensing system (QS) in Pseudomonas. sp. M18.

The two phz gene clusters were sequenced and the expressional features by GacA were analyzed using RT-PCR and phzA-lacZ transcriptional fusions, the regulation of GacA over QS system was studied also in P. sp. M18.

Two phenazine sturctural clusters, namely, phzA1-G1 and phzA2-G2 in P. sp. M18 shared 99% identities with those in P. aeruginosa PAO1. However, in the non-coding region downstream the phzA2-G2, P. sp. M18 has a three-144 bp-repeat sequence which does not exist in P. aeruginosa PAO1. PhzA1-G1 expressed at a higher level than phzA2-G2 in the wide type M18 strain. GacA functioned differently over these two phz gene clusters but negatively regulating the two clusters expression at the whole level, which was opposite to that in P. aeruginosa PAO1. The inactivation of gacA gene can reduce rhlI expression while has no effect on lasI expression, indicating that the phz gene expression regulated by GacA via QS was a minor part and the major phz expression was regulated by GacA through an unknown pathway instead of QS in P. sp. M18.

The different regulation of GacA activity on secondary metabolites and QS in P. sp. M18 and P. aeruginosa PAO1 may be the results imposed by the environmental selective pressure during evolution pathway.