ISOLATION AND ENTOMOTOXIC PROPERTIES OF THE XENORHABDUS-NEMATOPHILUS-F1 LECITHINASE

Xenorhabdus spp, and Photorhabdus spp,, entomopathogenic bacteria symb iotically associated with nematodes of the families Steinernematidae a nd Heterorhabditidae, respectively, were shown to produce different li pases when they were grown on suitable nutrient agar, Substrate specif icity studies showed that Photorhabdus spp, exhibited a broad lipase a ctivity, while most of the Xenorhabdus spp, secreted a specific lecith inase. Xenorhabdus spp, occur spontaneously in two variants, phase I a nd phase II. Only the phase I variants of Xenorhabdus nematophilus and Xenorhabdus bovienii strains produced lecithinase activity when the b acteria were grown on a solid lecithin medium (0.01% lecithin nutrient agar; 24 h of growth). Five enzymatic isomers responsible for this ac tivity were separated from the supernatant of a X. nematophilus F1 cul ture in two chromatographic steps, cation-exchange chromatography and C-18 reverse-phase chromatography. The substrate specificity of the X, nematophilus F1 lecithinase suggested that a phospholipase C preferen tially active on phosphatidylcholine could be isolated. The entomotoxi c properties of each isomer were tested by injection into the hemocoel s of insect larvae. None of the isomers exhibited toxicity with the in sects tested, Locusta migratoria, Galleria mellonella, Spodoptera litt oralis, and Manduca sexta. The possible role of lecithinase as either a virulence factor or a symbiotic factor is discussed.