Genomic Diversity and Evolution of Parasitism in Nematode-trapping Fungi

University dissertation from Microbial Ecology, Lund University

Abstract: Nematode-trapping fungi are soil-living organisms that have the ability to form infection structures, traps to capture nematodes. Many nematode species are parasites on plants and animals, which have resulted in an interest to use the nematode-trapping fungi as biological control agents. In order to understand more about the genomic diversity and evolution of parasitism among these fungi, several studies based on DNA sequence analysis were conducted. First, a phylogenetic tree was reconstructed using 18S ribosomal DNA (rDNA) sequences in order to classify and identify phylogenetic relationships between different species of nematode-trapping fungi. The obtained data was congruent with the trap morphology and it was revealed that the nematode-trapping fungi form a monophyletic clade, i. e. they have a common ancestor. Second, a population study of Duddingtonia flagrans, one of the most promising species for biological control of animal parasitic nematodes, was undertaken. The divergence of isolates from a worldwide collection as well as the mode of reproduction, dispersion and biogeography was investigated by using various DNA markers. The divergence time was estimated to 44000 years ago. Furthermore, it was found that the species has a clonal reproduction. There was no geographic pattern in the distribution of various genotypes, which indicates that D. flagrans has dispersed multiple times. Finally, a comparative transcriptome analysis was started using the nematode-trapping fungus Monacrosporium haptotylum. In total 4767 expressed sequence tags (ESTs) representing 2000 tentatively unique genes were sequenced from three different cDNA libraries: vegetative mycelium, developed traps, and traps infecting the model nematode Caenorhabditis elegans. The patterns of genes expressed in the different growth stages was to a large extent unique, only 7.6% of the sequenced transcripts were detected in more then one cDNA library. To comprehensively analyze the sequences, a web-based bioinformatic tool was developed. The software stores, perform similarity searches against an automatically downloaded protein database (non-redundant, GenBank) and displays the result in images as well as tables. Comparative analyses of annotated sequences indicated a number of differences in metabolic and cellular functions between the vegetative mycelium, knobs and fungus infecting C. elegans.

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