Antibiotic production in relation to bacterial growth and nematode development in Photorhabdus–Heterorhabditis infected Galleria mellonella larvae

The population of Photorhabdus luminescens C9, bacterial symbiont of the entomopathogenic nematode, Heterorhabditis megidis 90, increased rapidly to 1.2–2.6×10 9 cells g −1 wet Galleria mellonella larvae within 24 h of nematode infection of the larvae, and maintained a relatively constant level (1.2–2.0×10 10 cells g −1) through the entire 14-day period of nematode development. The antibiotic, 3,5-dihydroxy-4-isopropylstilbene, was produced by P. luminescens C9 after 24 h of nematode infection, increased rapidly at 2–5 days postinfection and remained at a level of 3000–3600 μg g −1 wet larvae until about 21 days, decreasing gradually thereafter. The early production and continued presence of a relatively large amount of 3,5-dihydroxy-4-isopropylstilbene in the infected insect supports the hypothesis that the antibiotics produced by the bacterial symbiont help minimize competition from other microorganisms and prevents the putrefaction of the nematode-infected insect cadaver.