Phase Variation in Xenorhabdus nematophilus

Abstract

Xenorhabdus nematophilus is a symbiotic bacterium that inhabits the intestine of entomopathogenic nematodes. The bacterium-nematode symbiotic pair is pathogenic for larval-stage insects. The phase I cell type is the form of the bacterium normally associated with the nematode. A variant cell type, referred to as phase II, can form spontaneously under stationary-phase conditions. Phase II cells do not elaborate products normally associated with the phase I cell type. To better define phase variation in X. nematophilus, several strains (19061, AN6, F1, N2-4) of this bacterium were analyzed for new phenotypic traits. An analysis of pathogenicity in Manduca sexta larvae revealed that the phase II form of AN6 (AN6/II) was significantly less virulent than the phase I form (AN6/I). The variant form of N2-4 was also avirulent. On the other hand, F1/II and 19061/II were as virulent as the respective phase I cells. Strain 19061/II was found to be motile, and AN6/II regained motility when the bacteria were grown in low-osmolarity medium. In contrast, F1/II remained nonmotile. The phase II cells did not produce the outer membrane protein, OpnB, that is normally induced during the stationary phase. Both phase I and phase II cells were able to support nematode growth and development. These findings indicate that while certain phenotypic traits are common to all phase II cells, other characteristics, such as virulence and motility, are variable and can be influenced by environmental conditions.

The global regulator Lrp contributes to mutualism, pathogenesis and phenotypic variation in the bacterium Xenorhabdus nematophila

“…In the absence of X. nematophila, S. carpocapsae reproduction fails to occur and nematode reproductive organs fail to form normally (Poinar and Thomas, 1966). Heat-killed or fractionated X. nematophila do not support nematode development (Volgyi et al, 1998;C.E. Cowles and H. Goodrich-Blair, unpubl.…”

“…The fact that secondary form variants are virulent towards insects and colonize nematodes (Volgyi et al, 1998;K.N. Cowles and H. Goodrich-Blair, unpubl.…”

Type 1 fimbriae of insecticidal bacterium Xenorhabdus nematophila is necessary for growth and colonization of its symbiotic host nematode Steinernema carpocapsiae

“…The proteins were transferred and blotted with anti-FliC antibody. Protease activity in the extracellular medium was determined by the gelatin plate assay (Volgyi et al, 1998). Extracellular lipase production was determined by a halo surrounding the colony of bacterial culture on Tween 20 and 80 agar plates as described previously (Thaler et al, 1998).…”

“…For the isolation of axenic eggs, nematodes were cultivated on wild-type Xenorhabdus lawn grown on oil agar plate (nutrient broth, 16 g; yeast extract, 5 g; vegetable oil, 5 g; phosphate buffer, pH 7.0, 15 ml and bacto agar, 15 g) (Volgyi et al, 1998). Briefly, 500-800 IJs were spread on the bacterial lawn and incubated at room temperature for 5-7 days.…”

Phenotypic variation and host interactions of Xenorhabdus bovienii SS‐2004, the entomopathogenic symbiont of Steinernema jollieti nematodes

“…All Xenorhabdus species reported to date undergo phenotypic variation characterized by the switching between two cell types known as primary and secondary forms. Although the phenotypic differences between primary and secondary forms can vary depending on strain and species (Akhurst and Boemare, 1990), typically the primary, but not secondary form cells are motile, pigmented, agglutinate red blood cells and produce fimbriae, haemolysins, proteases, antimicrobials and crystalline inclusion bodies Volgyi et al, 1998;Forst and Clarke, 2002;Smits et al, 2006). Xenorhabdus bacteria isolated from nematode hosts typically are in the primary form, but in laboratory culture conditions some cells convert to the secondary form.…”