Yadav Shruti, Frazer Joanna, Banga Ashima, Pruitt Katherine, Harsh Sneh, Jaenike John, Eleftherianos Ioannis
Infection and Innate Immunity Lab, Department of Biological Sciences, George Washington University, Washington, District of Columbia, United States of America.
Thomas Jefferson High School for Science and Technology, Alexandria, Virginia, United States of America.
PLoS One. 2018 Feb 21;13(2):e0192183. doi: 10.1371/journal.pone.0192183. eCollection 2018.
Associations between endosymbiotic bacteria and their hosts represent a complex ecosystem within organisms ranging from humans to protozoa. Drosophila species are known to naturally harbor Wolbachia and Spiroplasma endosymbionts, which play a protective role against certain microbial infections. Here, we investigated whether the presence or absence of endosymbionts affects the immune response of Drosophila melanogaster larvae to infection by Steinernema carpocapsae nematodes carrying or lacking their mutualistic Gram-negative bacteria Xenorhabdus nematophila (symbiotic or axenic nematodes, respectively). We find that the presence of Wolbachia alone or together with Spiroplasma promotes the survival of larvae in response to infection with S. carpocapsae symbiotic nematodes, but not against axenic nematodes. We also find that Wolbachia numbers are reduced in Spiroplasma-free larvae infected with axenic compared to symbiotic nematodes, and they are also reduced in Spiroplasma-containing compared to Spiroplasma-free larvae infected with axenic nematodes. We further show that S. carpocapsae axenic nematode infection induces the Toll pathway in the absence of Wolbachia, and that symbiotic nematode infection leads to increased phenoloxidase activity in D. melanogaster larvae devoid of endosymbionts. Finally, infection with either type of nematode alters the metabolic status and the fat body lipid droplet size in D. melanogaster larvae containing only Wolbachia or both endosymbionts. Our results suggest an interaction between Wolbachia endosymbionts with the immune response of D. melanogaster against infection with the entomopathogenic nematodes S. carpocapsae. Results from this study indicate a complex interplay between insect hosts, endosymbiotic microbes and pathogenic organisms.
内共生细菌与其宿主之间的关联代表了一个复杂的生态系统，存在于从人类到原生动物等各类生物体中。已知果蝇物种天然携带沃尔巴克氏体和螺原体这两种内共生菌，它们对某些微生物感染具有保护作用。在此，我们研究了内共生菌的有无是否会影响黑腹果蝇幼虫对携带或缺乏共生革兰氏阴性菌嗜线虫致病杆菌（分别为共生线虫或无菌线虫）的斯氏线虫感染的免疫反应。我们发现，单独存在的沃尔巴克氏体或与螺原体共同存在时，可促进幼虫在感染斯氏线虫共生线虫后的存活，但对无菌线虫感染则无此作用。我们还发现，与感染共生线虫的幼虫相比，感染无菌线虫的无螺原体幼虫体内的沃尔巴克氏体数量减少；与感染无菌线虫的无螺原体幼虫相比，含有螺原体的幼虫体内的沃尔巴克氏体数量也减少。我们进一步表明，在没有沃尔巴克氏体的情况下，斯氏无菌线虫感染会诱导Toll信号通路，而共生线虫感染会导致无内共生菌的黑腹果蝇幼虫体内酚氧化酶活性增加。最后，两种类型的线虫感染都会改变仅含有沃尔巴克氏体或同时含有两种内共生菌的黑腹果蝇幼虫的代谢状态和脂肪体脂滴大小。我们的结果表明，沃尔巴克氏体内共生菌与黑腹果蝇针对昆虫病原线虫斯氏线虫感染的免疫反应之间存在相互作用。本研究结果表明昆虫宿主、内共生微生物和致病生物体之间存在复杂的相互作用。
