Deoxyribonucleic Acid Relatedness and Phenotypic Study of the Genus Xenorhabdus

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Abstract
A collection of 30 clones derived from 20 luminous and nonluminous Xenorhabdus strains was studied by using deoxyribonucleic acid (DNA) relatedness and electron microscopy, as well as growth factor requirement, nutritional ability, and other biochemical tests. Nonluminous Xenorhabdus cells each contained a crystal-like structure, whereas the cells of luminous strains each contained an accumulation of amorphous material associated with mesosomes and microtubules of unknown function. Two DNA relatedness groups of nonluminous strains were delineated, one of which corresponded to Xenorhabdus nematophilus, a species associated with the nematode Steinernema feltiae (= Neoplectana carpocapsae). The other group contained yellow-pigmented bacteria associated with Steinernema bibionis and new Steinernema species. No definite phenotypic characteristic (except pigmentation) separated the two DNA relatedness groups of nonluminous Xenorhabdus strains. Four DNA relatedness groups were delineated among the luminous clones studied. These four groups could be separated by biochemical tests. Unfortunately, different clones derived from the same strain belonged to different DNA relatedness groups. This happened with the type strain of Xenorhabdus luminescens.