Insecticidal Activity and Genetic Characterization of Four Bacterial Isolates of Xenorhabdus and Photorhabdus Associated with Entomopathogenic Nematodes (original) (raw)

Three Photorhabdus luminescens and one Xenorhabdus nematophila strains were isolated from Heterorhabditis bacteriophora and Steinernema carpocapsae nematodes, respectively. The nematodes were isolated from soil samples collected from four Egyptian governorates using Galleria larvae as bait. Toxicity of the four isolates on the 3 rd instar wax moth larvae of Galleria mellonella L. showed that BA1 and MH had the highest mortality (66.6 and 60%, respectively) at a concentration of 5.35 × 10 3 after 9 days using direct feeding. By using direct spray, BA1 displayed the highest mortality (73.3%) followed by MH (66.6%) and BAA1 (60%) after 8 days at the same concentration. Using direct injection, BA1 and BA2 revealed complete mortality after 48 h and after 24 h BA1 showed 90 and 70% mortality with 0.67 × 10 3 and 0.33 × 10 3 concentrations, respectively followed by BA2 with 80 and 70% mortality with 1.04 × 10 3 and 0.52 × 10 3 concentrations, respectively. The other two isolates showed complete mortality after 72 h. Moreover, at 2.67 × 10 3 BAA1 showed a high mortality (60%) after 8 days of direct spray. BA2 displayed a similar high mortality after 120 h of direct feeding and spray with 60% using three concentrations (8.35 × 10 3 , 2.08 × 10 3 and 1.04 × 10 3). RAPD analysis revealed 46 polymorphic fragments that ranged in size from 7.25 to 0.15 kb. The mean percentage of polymorphism shown by the four primers was 67.6%, decreasing in this order: UBC-37 (75%), UBC-89 (73.3%), UBC-16 (65%) and UBC-28 (58.8%). BA2, belonging to Xenorhabdus nematophila, had the highest number (6) of specific fragments, followed by MH with two and both BA1 and BAA1 with one. SDS-PAGE of proteins displayed remarkable genetic variation between the four isolates. Several toxic protein bands were detected among the four isolates, for instance 40 kD in BA2, 283 kD in BA1, BAA1 and MH and 37 kD in BA1 and MH.