Biosurfactants produced by Peudomonas fluorescens and soft-rotting of harvested florets of broccoli and cauliflower

Abstract

Mini-Tn5 transposon mutagenesis of a soft-rotting isolate of Pseudomonas fluorescens strain 123 produced six mutant phenotypes with altered pathogenicity and inability to produce a biosurfactant involved in dispersing P. fluorescens cells in a surface aqueous environment. The mutants isolated showed in vivo growth characteristics identical to those of the wild type, but variations in their ability to reduce surface tension of water and to grow in liquid medium containing hexadecane. One of these mutants (EG3) with reduced pathogenicity on broccoli and cauliflower exhibited a restored pathogenic phenotype when complemented with a 7.1-kb segment of P. fluorescens genomic DNA. The loss of aqueous-surface-tension activity in mutants suggests that a biosurfactant may contribute to pathogenicity and enhance pathogen invasion of host tissues.