Role of cyclic lipopeptide surfactants in bacterial defense against protozoan predation

Cyclic lipopeptides (CLPs) are produced by a diversity of bacterial genera, possess biosurfactant activity, and play a key role in a multiplicity of natural functions for the producing bacteria, including swarming motility and biofilm formation. CLPs have the capacity to disrupt membrane integrity leading to the cell lysis of certain microbial life stages, including oomycete zoospores. This study shows that the CLPs massetolide A and viscosin produced by the bacteria Pseudomonas fluorecens strains SS101 and SBW25 lead to lysis of protozoan trophozoites and confer protection from predation by the amoebaflagellate Naegleria americana. In vitro, massetolide A-producing SS101 and viscosin-producing SBW25 were significantly less susceptible to grazing by N. americana than the corresponding CLP-deficient massA mutant 10.24 and viscA mutant of SBW25. Genetic complementation of the massA mutation in 10.24 restored massetolide A biosynthesis and protection from N. americana predation. Populations of mutant 10.24 exhibited a more rapid decline in bulk soil relative to the parental strain, with SS101 maintaining a population approximately one order of magnitude greater than the surfactant-deficient mutant two weeks post-inoculation. Collectively these results show, for the first time, that CLPs produced by Pseudomonas contribute to survival in soil and are potent metabolites in the bacterial defense against protozoan predation