Taxonomic Study of Xenorhabdus, a Genus of Bacteria Symbiotically Associated with Insect Pathogenic Nematodes

Abstract

The taxonomy of the bacteria symbiotically associated with the insect-pathogenic nematodes Neoaplectana and Heterorhabditis was examined. The bacteria studied were isolated from 33 populations obtained from Australasia, Europe, and the United States. The symbionts of all species of Neoaplectana and Heterorhabditis examined were members of the genus Xenorhabdus, but they differed in several respects from the description of the genus Xenorhabdus, including the guanine-plus-cytosine content of the deoxyriboneucleic acid and the production of acid from carbohydrates. All bacteria isolated from Heterorhabditis spp. were identified as members of Xenorhabdus luminescens. The bacteria isolated from one Neoaplectana species were similar and were distinguishable from the bacteria isolated from other Neoaplectana species. The following three subspecies of Xenorhabdus nematophilus are proposed: Xenorhabdus nematophilus subsp. nematophilus (bacteria symbiotic with Neoaplectana feltiae [= Neoaplectana carpocapsae]; type strain ATCC 19061), Xenorhabdus nematophilus subsp. bovienii (bacteria symbiotic with Neoaplectana bibionis; type strain, UQM 2210T), and Xenorhabdus nematophilus subsp. poinarii (bacteria symbiotic with Neoaplectana glaseri; type strain, UQM 2216). These subspecies vary in host nematode, pigmentation, maximum temperature for growth, responses to tests for phenylalanine deaminase by secondary-form isolates and for lipase (Tween 80 test) and lecithinase by primary-form isolates, and coloration of primary-form isolates on MacConkey agar and media containing bromthymol blue.