X. innexi nematode colonization levels and in vitro growth rate are lower than other Xenorhabdus species. a
S. carpocapsae or (b) S. scapterisci nematodes were reared on lawns of their respective symbionts, X. nematophila and X. innexi, engineered to express the green fluorescent protein. Approximately 100 infective juveniles of each nematode species emerging from these lawns were examined by fluorescence microscopy to visualize bacterial colonization of the nematode receptacle and two representative images are shown for each nematode. All colonized S. scapterisci nematodes had smaller regions of green fluorescence in the receptacle than did colonized S. carpocapsae. When individual bacterial cells could be resolved only 2–3 cells were apparent within S. scapterisci nematodes. Both nematode species were colonized at similar frequencies (~92–97%). Bb: basal bulb; b: bacteria. c
X. bovienii (red squares), X. nematophila (blue circles), and X. innexi (green triangles) bacteria were subcultured into LB medium and monitored for growth based on optical density (OD600).
X. innexi displayed a longer lag time, slower growth rate, and lower final cell densities than the other two bacterial species, . X. innexi density became significantly different from that of X. nematophila and X. bovienii after 6 h and remained significantly different for the remainder of the experiment (***: P < 0.002, 2-way ANOVA at each time point with Tukey’s multiple comparisons test), and the overall growth curve was significantly different using Extra sum-of-squares F text (P = 0.0001)