Evidence and characterization of a gene cluster required for the production of viscosin, a lipopeptide biosurfactant, by a strain of Pseudomonas fluorescens

The genetic control of viscosin production was examined in a strain of Pseu domonas fluorescens (PfA7B) that causes broccoli head rot. Viscosin is a po tent lipopeptide biosurfactant that enables the bacteria to come into intim ate contact with the difficult-to-wet waxy heads of broccoli. Tn5 mutagenes is completely disrupted viscosin production as shown by HPLC analysis of th e mutagenized cell lysates. The Vis(-) mutants retained their pectolytic ca pability and were able to decay potato slices. On broccoli, however, the Vi s(-) mutants caused decay of wounded florets, but the decay failed to sprea d to adjacent nonwounded florets as had occurred with the wild-type PfA7B. Triparental matings of the Vis(-) mutants with their corresponding wild-typ e clones and the helper Escherichia coli HB101 carrying the mobilization pl asmid pPK2013 resulted in three stable viscosin-producing transconjugants t hat caused typical decay of broccoli tissue. Linkage maps of clones and pro tein profiles showed that a 25-kb chromosomal DNA region of PfA7B affected the production of three high molecular mass proteins required for viscosin synthesis. These proteins, approximately 218, 215, and 137 kDa in size, lik ely compose a synthetase complex that assembles the nine amino acid peptide of viscosin and subsequently attaches this to the hydrophobic fatty acid c omponent of the molecule. A probe made from this DNA region hybridized with DNA fragments of other phytopathogenic pseudomonads to varying degrees.