Emelianoff Vanya, Sicard Mathieu, Le Brun Nathalie, Moulia Catherine, Ferdy Jean-Baptiste
Laboratoire Génome, Populations, Interactions, Adaptation, c.c. 63 CNRS-UM2-IFREMER UMR 5171, Université de Montpellier 2, Place Eugène Bataillon, 34095, Cedex 05 Montpellier, France.
Parasitol Res. 2007 Feb;100(3):657-9. doi: 10.1007/s00436-006-0284-y. Epub 2006 Aug 30.
Steinernema species are entomopathogenic nematodes associated with Xenorhabdus bacteria. The life cycle of these associations is composed of two stages: (1) a free stage in the soil, where infective juveniles (IJs), which carry bacteria in their guts, search for new insect hosts; and (2) a parasitic stage, where the IJs infect insects, release their Xenorhabdus symbionts and reproduce in order to produce new IJs. Previous studies clearly showed benefits to the association for several Steinernema species during the parasitic stage. Nevertheless, no study has so far explored, during the free stage, the existence of costs or benefits to the association for different Steinernema. Here, we compared the survival of both symbiotic and aposymbiotic IJs in two nematode species: (1) Steinernema carpocapsae-exhibiting IJs that carry a high number of Xenorhabdus cells in their guts; and (2) its closely relative species, S. scapterisci-exhibiting IJs, that carry very few Xenorhabdus cells in their guts. We showed that the bacterial symbionts were costly for S. carpocapsae by increasing IJs' mortality but not for S. scapterisci. This difference in cost induced by bacteria to IJs during the free stage could be correlated with the difference in the numbers of bacteria carried by IJs of each nematode species.
斯氏线虫属是与发光杆菌属细菌相关的昆虫病原线虫。这些共生关系的生命周期由两个阶段组成：（1）在土壤中的自由阶段，携带细菌的感染性幼虫（IJs）在肠道中寻找新的昆虫宿主；（2）寄生阶段，感染性幼虫感染昆虫，释放其共生的发光杆菌属细菌并繁殖以产生新的感染性幼虫。先前的研究清楚地表明，在寄生阶段，几种斯氏线虫属物种的共生关系存在益处。然而，到目前为止，尚无研究探讨在自由阶段，不同斯氏线虫属物种的共生关系是否存在成本或益处。在此，我们比较了两种线虫物种中具共生细菌和无共生细菌的感染性幼虫的存活率：（1）小卷蛾斯氏线虫——其感染性幼虫在肠道中携带大量发光杆菌属细胞；（2）其近缘物种，沙氏斯氏线虫——其感染性幼虫在肠道中携带极少发光杆菌属细胞。我们发现，共生细菌对小卷蛾斯氏线虫的感染性幼虫来说是有成本的，因为它增加了感染性幼虫的死亡率，但对沙氏斯氏线虫则不然。在自由阶段，细菌对感染性幼虫造成的这种成本差异可能与每个线虫物种感染性幼虫携带的细菌数量差异有关。
