School of Animal and Comparative Biomedical Sciences, The University of Arizona, Tucson, AZ 85721, USA.
School of Animal and Comparative Biomedical Sciences, The University of Arizona, Tucson, AZ 85721, USA; Department of Entomology, The University of Arizona, Tucson, AZ 85721, USA.
J Invertebr Pathol. 2018 Mar;153:65-74. doi: 10.1016/j.jip.2018.02.015. Epub 2018 Feb 16.
Steinernema nematodes and their Xenorhabdus partners form an obligate mutualistic association. This partnership is insecticidal to a wide range of insects. Steinernema rely on their Xenorhabdus partner to produce toxins inside the insect cadaver to liberate nutrients from the insect, as well as antimicrobials to sterilize the cadaver, thus creating a suitable environment for reproduction. In return, Steinernema vector their Xenorhabdus between insect hosts. Disruption of this partnership may affect the success of both partners. For instance, when Steinernema associates with non-cognate symbionts, their virulence and reproductive fitness are affected. In this study, we examined the effect of symbiotic (cognate and non-cognate) and non-symbiotic bacteria on maturation time, gonad postembryonic development, and sex ratio of first-generation Steinernema adults. Two Steinernema spp. were considered: S. feltiae SN and S. carpocapsae All. In vitro assays were carried out by pairing each nematode sp. with symbiotic (cognate and non-cognate) Xenorhabdus, and with non-symbiotic bacteria (Serratia proteamaculans). Additionally, for comparative purposes, we also considered adult nematodes reared in vivo in Galleria mellonella larvae to assess nematode development under natural conditions. Results from this study showed non-symbiotic Serratia proteamaculans did not support adult development of S. feltiae but it allowed development of S. carpocapsae adults. Sex ratio decreased from 2:1 to 1:1 (female: male) when S. carpocapsae adults were reared with the non-symbiotic S. proteamaculans. Cognate or non-cognate Xenorhabdus spp. and/or strains did not change the sex ratio of any of either Steinernema spp. tested. Morphometric analysis also revealed that bacterial conditions influenced adult size and gonad postembryonic development in both Steinernema species. Body size (length and width), and gonad length in both S. feltiae males and females, were significantly reduced when reared with a non-cognate Xenorhabdus species. In S. carpocapsae, males exhibited an enhanced body size (length and width) and gonad length when reared with a non-cognate X. nematophila strain. S. carpocapsae females also exhibited an enhanced gonad length when reared with a non-cognate X. nematophila strain. S. carpocapsae males and females were underdeveloped when reared with the non-symbiotic S. proteamaculans, and exhibited reduced body sizes and gonad lengths. We conclude that development of first-generation adults of both Steinernema spp. tested, in particular time to adult maturation as well as body and gonad size were directly influenced by the bacterial symbionts they were cultured with. However, response to the culture conditions was species specific.
斯氏线虫及其共生的黄杆菌形成了一种专性互利共生关系。这种共生关系对广泛的昆虫具有杀虫作用。斯氏线虫依靠其共生的黄杆菌在昆虫尸体内部产生毒素，以从昆虫体内释放营养物质，并产生抗菌物质来对尸体进行消毒，从而为繁殖创造合适的环境。作为回报，斯氏线虫在昆虫宿主之间传播其共生的黄杆菌。这种共生关系的破坏可能会影响到两个共生体的成功。例如，当斯氏线虫与非同源共生体结合时，其毒力和生殖适应性会受到影响。在这项研究中，我们研究了共生（同源和非同源）和非共生细菌对第一代斯氏线虫成虫成熟时间、胚胎后性腺发育和性别比例的影响。研究考虑了两种斯氏线虫： S. feltiae SN 和 S. carpocapsae All。通过将每种线虫与共生（同源和非同源）的 Xenorhabdus 以及非共生细菌（Serratia proteamaculans）配对，进行了体外检测。此外，为了进行比较，我们还考虑了在 Galleria mellonella 幼虫中体内饲养的成年线虫，以评估在自然条件下线虫的发育情况。研究结果表明，非共生的 Serratia proteamaculans 不能支持 S. feltiae 的成虫发育，但可以支持 S. carpocapsae 的成虫发育。当 S. carpocapsae 成虫与非共生的 Serratia proteamaculans 一起饲养时，其性别比例从 2:1 下降到 1:1（雌性：雄性）。同源或非同源 Xenorhabdus 物种和/或菌株没有改变任何一种斯氏线虫的性别比例。形态测量分析还表明，细菌条件影响了两种斯氏线虫的成虫大小和胚胎后性腺发育。当与非同源 Xenorhabdus 物种一起饲养时，两种 S. feltiae 雄性和雌性的成虫体型（长度和宽度）以及性腺长度均显著减小。在 S. carpocapsae 中，当与非同源的 X. nematophila 菌株一起饲养时，雄性的体型（长度和宽度）以及性腺长度都会增强。当与非同源的 X. nematophila 菌株一起饲养时，S. carpocapsae 雌性的性腺长度也会增强。当与非共生的 Serratia proteamaculans 一起饲养时，S. carpocapsae 雄性和雌性的发育不良，体型和性腺长度均减小。我们的结论是，测试的两种斯氏线虫第一代成虫的发育，特别是成虫成熟时间以及体型和性腺大小，直接受到它们所培养的共生细菌的影响。然而，对培养条件的反应是种特异性的。
