Morphological and Functional Dimorphism in Xenorhabdus spp., Bacteria Symbiotically Associated with the Insect Pathogenic Nematodes Neoaplectana and Heterorhabditis

Abstract

Xenorhabdus spp., entomopathogenic bacteria symbiotically associated with the nematodes Neoaplectana and Heterorhabditis, occur in two forms. In general, only one form, designated the primary form, is transmitted into new hosts by the infective stage of the nematode. The significance of the relationship between the two forms has been examined with X. nematophilus, the symbiont of N. feltiae. The forms of X. nematophilus can be differentiated by their colony characteristics but by only two biochemical tests. The two forms of X. nematophilus are equally pathogenic when injected into the haemocoel of Galleria larvae. However, the primary form when injected into Galleria larvae with axenic nematodes provides better conditions for reproduction of the nematodes than the secondary form, for which a role has not been determined. Although the primary form readily converts to the secondary form in vitro and occasionally in vivo, the secondary form is usually stable. Possible causes of the instability have been investigated.

Description of Xenorhabdus khoisanae sp. nov., the symbiont of the entomopathogenic nematode Steinernema khoisanae

“…Cultures were obtained indirectly from the nematodes by sampling the haemocoel of wax moth larvae (Galleria mellonella L.), which was plated onto nutrient agar (Biolab Diagnostics), supplemented with 0.004 % (w/v) triphenyltetrazolium chloride and 0.025 % (w/v) bromothymol blue (NBTA) according to the procedure described by Akhurst (1980). Plates were incubated at 26 u C for 72 h and blue-green colonies were randomly selected for identification and further characterization.…”

Providencia vermicola sp. nov., isolated from infective juveniles of the entomopathogenic nematode Steinernema thermophilum

“…Isolation was performed as described by Akhurst (1980): a mixture of infective juveniles (IJs) of nematodes of Steinernema thermophilum belonging to different age groups, isolated from different larvae of the greater wax moth (Galleria mellonella), were surface sterilized in 0?1 % Hyamine 106 (methylbenzethonium chloride; Spectrum Chemicals & Laboratory Products) for 15-30 min. Nematodes were then washed three times in sterilized water in order to remove traces of Hyamine.…”

The effect of transferring methods on successive axenic culture of Stein ern ema kushidai(Nemetoda: Steinernematidae)

“…This nematode is accompanied by a symbiotic bacterium identified as Xenorhabudus japonicus (11). Symbiotic bacteria associated with the genera Steinernema and Heterorhabditis are demonstrated to play important roles in killing their host insects and also in propagation of nematodes (1). Therefore, bioassay using axenic S. kushidai may be useful to analyze the efficacious pathogenicity of S. kushidai against white grubs.…”