Figure 1.

Schematic Overview of Model Nematode-Bacterium Symbioses: Symbiont Location and Life Cycle>

A: Xenorhabdus and Photorhabdus (green) are located within infective juveniles (environmental stage) of Steinernema and Heterorhabditis nematodes respectively. The bacteria are located in the lumen between intestinal epithelial cells (grey with dark grey nuclei) (insets).

B: The infective juveniles of Sterinernema and Heterorhabditis parasitize insect hosts. The nematodes and bacteria kill the insect and reproduce within the insect cadaver. The nematodes then re-associate with their bacterial symbiont and migrate away from the cadaver into the environment to seek new hosts.

C: The ecotsymbiont (green) of Laxus oneistus (grey) is located on the outside of all nematode life stages. The bacteria are arranged in a perpendicular fashion to the exterior of the nematode (inset).

D. L. oneistus nematodes grow and reproduce in the sediment of the sea floor. Their thiotrophic ectosymbiont profits from nematode migrations in oxygen and sulfide gradients (see text for more details).

E. The Wolbachia symbiont (green) of Brugia malayi nematodes (grey) are localized to the hypodermal cells of the lateral chords in all nematode life stages and the reproductive tissues of females. These bacteria are intracellular (inset).

F. B. malayi is transmitted to a human host through a mosquito vector. The nematodes undergo reproduction within the human host and produce a larval stage that can be taken up by new mosquitoes. Larval stages grow within the mosquito and can then infect new human hosts when the mosquito takes a blood meal.