Host-parasite interaction in the endobiotic basal fungal lineage Nephridiophagidae and its insect host

大多数真菌门包含昆虫致病谱系，具有不同程度的特异性。一个高度专业化但很少被研究的群体是单细胞肾双噬菌，一种感染昆虫马尔比氏小管的内生真菌。在这里，我们想研究它们对宿主适应性的影响。我们的假设是被肾双噬虫感染的宿主的适应性降低了。将测试不同的适应性成分，包括生殖成功率、身体适应性和生理适应性相关，如免疫能力、马尔比氏小管的功能和对化学杀虫剂的敏感性。德国小蠊是我们实验的理想试验生物。对卵壳进行无菌洗涤，可以产生无寄生虫的种群，这些种群可以通过喂养被寄生的马尔比氏小管来特异性地感染噬肾线虫。此外，短的发育时间和快速的繁殖保证了足够数量的动物的生产。这也促进了有关人口发展和生殖成功的实验。在第二部分中，我们想要揭示内生生物的生命周期，并建立系统发育关系。从口服噬肾菌孢子发育的早期生命阶段是完全未知的。我们假设孵化出的孢子质体具有运动性，并主动通过肠壁和血淋巴感染最终栖息地，即马尔比氏小管。体外实验将采用不同的物理和化学刺激来诱导孢子的孢子质孵化。通过光学显微镜（如延时视频显微镜，细胞骨架的荧光免疫染色）观察运动的各个方面。早期的原位发育将在口腔感染或将孢子注射到血淋巴后进行研究（例如，用荧光染色剂制备整个肠道，用PCR检测低数量的肾双噬菌）。进一步的重点是深化肾双噬菌的分子系统发育研究，以便在早期分化的真菌类群中找到确切的位置。最近的研究结果表明，肾噬菌可能是一个新的基础真菌门，接近壶菌门。为了更好地支持系统发育树的重建，有必要分析更多的肾噬菌种类和使用更多的遗传标记。

Most fungal phyla contain entomopathogenic lineages with different degrees of specificity. A highly specialized but hardly studied group are the unicellular nephridiophagids, endobiotic fungi that infect the Malpighian tubules of insects. Here we want to investigate their effect on the fitness of their hosts. Our hypothesis is that the fitness of Nephridiophaga-infected hosts is reduced. Different fitness components will be tested, including reproductive success, physical fitness, and physiological fitness correlates such as immunocompetence, functionality of the Malpighian tubules, and susceptibility to chemical insecticides. The German cockroach Blattella germanica is an ideal test organism for our experiments. Sterile washing of the egg-cases enables production of parasite-free populations which can be specifically infected with Nephridiophaga by feeding parasitized Malpighian tubules. Further, the short development time and quick reproduction ensures the production of sufficient numbers of animals. This also facilitates experiments concerning population development and reproductive success. In a second part we want to unravel the life cycle of the endobionts and also establish the phylogenetic relationships. The early life stages which develop from orally ingested spores of Nephridiophaga are completely unknown. We hypothesize that the hatched sporoplasms are motile and actively pass through the gut wall and haemolymph to infect the final habitat, i.e. the Malpighian tubules. In-vitro experiments using different physical and chemical stimuli will be performed to induce hatching of the sporoplasm from the spore. Aspects of motility are observed by light microscopy (e.g. time lapse video microscopy, fluorescence immune staining of cytoskeleton). The early in-situ development will be studied after oral infection or after injection of spores into the haemolymph (e.g. whole mount gut preparations with fluorescent stains, PCR for detection of low numbers of Nephridiophaga). A further point of emphasis is to deepen the molecular phylogenetic studies of nephridiophagids in order to find the exact position within the early diverging fungal groups. Recent results support that nephridiophagids may represent a new basal fungal phylum close to the Chytridiomycota s.l. For a well-supported reconstruction of the phylogenetic tree it is necessary to analyze more nephridiophagid species and use more genetic markers.