Pathogenicity of Moraxella osloensis, a bacterium associated with the nematode Phasmarhabditis hermaphrodita, to the slug Deroceras reticulatum

Moraxella osloensis, a gram-negative bacterium, is associated with Phasmarh abditis hermaphrodita, a nematode parasite of slugs. This bacterium-feeding nematode has potential for the biological control of slugs, especially the grey garden slug, Deroceras reticulatum. Infective juveniles of P. hermaph rodita invade the shelf cavity of the slug, develop into self-fertilizing h ermaphrodites, and produce progeny, resulting in host death. However, the r ole of the associated bacterium in the pathogenicity of the nematode to the slug is unknown. We discovered that M. osloensis alone is pathogenic to D. reticulatum after injection into the shell cavity or hemocoel of the slug. The bacteria from 60-h cultures were more pathogenic than the bacteria fro m 40-h cultures, as indicated by the higher and more rapid mortality of the slugs injected with the former. Coinjection of penicillin and streptomycin with the 60-h bacterial culture reduced its pathogenicity to the slug. Fur ther work suggested that the reduction and loss of pathogenicity of the age d infective juveniles of P. hermaphrodita to D. reticulatum result from the loss of M. osloensis from the aged nematodes. Also, axenic J1/J2 nematodes were nonpathogenic after injection into the shell cavity. Therefore, we co nclude that the bacterium is the sole killing agent of D. reticulatum in th e nematode-bacterium complex and that P. hermaphrodita acts only as a vecto r to transport the bacterium into the shell cavity of the slug. The identif ication of the toxic metabolites produced by Al. osloensis is being pursued .