Biological characterization of white line-inducing principle (WLIP) produced by Pseudomonas reactans NCPPB1311

The biological activities of the lipodepsipeptides (LDP) white line-inducing principle (WLIP), produced by Pseudomonas reactans NCPPB1311, and tolaasin I, produced by P. tolaasii NCPPB2192, were compared. Antimicrobial assays showed that both LDP inhibited the growth of fungi-including the cultivated mushrooms Agaricus bisporus, Lentinus edodes, and Pleurotus spp.-chromista, and gram-positive bacteria. Assays of the two LDP on blocks of Agaricus bisporus showed their capacity to alter the mushrooms' pseudo-tissues though WLIP was less active than that of tolaasin I. Contrary to previous studies, tolaasin I was found to inhibit the growth of gram-negative bacteria belonging to the genera Escherichia, Erwinia, Agrobacterium, Pseudomonas, and Xanthomonas. The only gram-negative bacterium affected by WLIP was Erwinia carotovora subsp. carotovora. Both WLIP and tolaasin I caused red blood cell lysis through a colloid-osmotic shock mediated by transmembrane pores; however, the haemolytic activity of WLIP was greater than that of tolaasin I. Transmembrane pores, at a concentration corresponding to 1.5 X C-50, showed a radius between 1.5 and 1.7 +/- 0.1 nm for WLIP and 2.1 +/- 0.1 nm for tolaasin I. The antifungal activity of WLIP together with the finding that avirulent morphological variants of P reactans lack WLIP production suggests that WLIP may play an important role in the interaction of the producing bacterium P. reactans and cultivated mushrooms.