Discovery of new regulatory genes of lipopeptide biosynthesis in Pseudomonas fluorescens

Pseudomonas fluorescens SS101 produces the cyclic lipopeptide massetolide with diverse functions in antimicrobial activity, motility, and biofilm formation. To understand how massetolide biosynthesis is genetically regulated in SS101, c. 8000 random plasposon mutants were screened for reduced or loss of massetolide production. Of a total of 58 putative mutants, 45 had a mutation in one of the three massetolide biosynthesis genes massA, massB, or massC. For five mutants, the insertions were located in the known regulatory genes gacS, gacA, and clpP. For the remaining eight mutants, insertions were located in clpA, encoding the ClpP chaperone, in phgdh, encoding D-3-phosphoglycerate dehydrogenase, in the heat shock protein-encoding dnaK, or in the transmembrane regulatory gene prtR. Genetic, chemical, and phenotypic analyses showed that phgdh, dnaK, and prtR are indeed involved in the regulation of massetolide biosynthesis, most likely by transcriptional repression of the LuxR-type regulator genes massAR and massBCR. In addition to their role in massetolide biosynthesis, dnaK and prtR were found to affect siderophore and extracellular protease(s) production, respectively. The identification of new regulatory genes substantially extended insights into the signal transduction pathways of lipopeptide biosynthesis in P. fluorescens and into regulation of other traits that may contribute to its life-style in the rhizosphere.