Regulator of exopolysaccharide and type III secretion (RetS) is a hybrid sensor kinase/response regulator protein located on bacterial membrane, and essential for expression of numerous genes. In Pseudomonas aeruginosa, RetS modulates the phosphorylation state of another kinase GacS via a direct interaction.
Objective: The goal of this study is to study the effect of retS on the antibiotic 2,4-diacetyl-phloroglucinol (2,4-DAPG) production in P. fluorescens 2P24.
Methods: Production of 2,4-DAPG in strain 2P24 and its mutants was quantified by HPLC. To determine the effect of RetS on the Gac/Rsm pathway, the promoters of the small RNA genes rsmX/rsmY/rsmZ and regulatory genes rsmA/rsmE in the Rsm pathway were fused with a promoterless lacZ, and the promoter activities were measured in 2P24 and the retS-deficient mutants.
Results: Genetic inactivation of the retS in strain 2P24 increased the production of an uncharacterized red pigment and the antibiotic 2,4-DAPG. RetS negatively regulated the transcription of the small RNAs RsmX and RsmZ. In the retS and gacS double mutant or the retS and gacA double mutant, all the phenotypic changes caused by the retS deletion were reversed to the level of gacS or gacA single gene mutant.
Conclusion: In P. fluorescens 2P24, RetS negatively regulates the production of antibiotic 2,4-DAPG through the Gac/Rsm pathway.