Trans-specific nematicidal activity of Photorhabdus luminescens

Mixed culture filtrates of Photorhabdus luminescens isolated from Heterorha bditis bacteriophora H06 and from H. indica LN? had a toxic effect on axeni c H. bacteriophora H06 dauer juveniles. Single culture filtrates had no eff ect. When one filtrate originated from a secondary phase culture, the toxic effect was lost. Heat treatment of one of the filtrates to 80 degrees C de stroyed the effect. The toxin is probably synthesized de novo after mixing the culture supernatants of these two P. luminescens symbionts. Dilution of the filtrate reduced the effect, and it was lost when P. luminescens was c ultured for more than two days. Steinernema carpocapsae A24 was not affecte d by the mixture, and was affected only by the filtrate of primary phase P, luminescens H06. The toxic effect was recorded also when axenic dauer juve niles of H, bacteriophora were inoculated into a mixed bacterial culture of H06 and LN2. Inoculating monoxenic dauer juveniles of H. bacteriophora H06 into P. luminescens LN2 or into mixtures containing LN2 bacteria resulted in significant dauer juvenile mortality. These manifestations of the intera ction of bacteria to produce toxic effects on the non-symbiotic nematode (t rans-specific activity) may have an impact on competitive interactions when one insect host is infected by different nematode species.