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

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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.