Xenorhabdus gen. nov., a Genus of Entomopathogenic, Nematophilic Bacteria of the Family Enterobacteriaceae

A new genus, Xenorhabdus, is created to accommodate large, gram-negative, rod-shaped, facultatively anaerobic, entomopathogenic bacteria which are intimately associated with entomogenous nematodes. The normal habitat of these bacteria is the intestinal lumen of nematodes or the body cavity of host insects into which they have been introduced by the nematodes. The genus is placed in the family Enterobacteriaceae since the bacteria possess most of the important characteristics of this family. Xenorhabdus differs from other genera of Enterobacteriaceae in large cell size, failure to reduce nitrates to nitrites, intimate association with entomogenous nematodes, entomopathogenesis, and immunological characteristics. The type species is Xenorhabdus nematophilus (Poinar and Thomas) comb. nov. (synonym: Achromobacter nematophilus Poinar and Thomas). Xenorhabdus luminescens sp. nov., a bioluminescent, entomopathogenic bacterium isolated from the intestinal lumen of an entomogenous nematode, Heterorhabditis bacteriophora, is also described. In addition to their immunological differences, the two species are dissimilar in that X. luminescens is positive for bioluminescence and catalase activity, whereas X. nematophilus is not. The type strain of X. nematophilus is ATCC 19061, and that of X. luminescens is strain Hb (= ATCC 29999).