Thesis (Ph. D.)--University of Wisconsin--Madison, 1932. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Oomycetes are eukaryotic fungus-like microorganisms that are well known for the pathogenic species contained within the group causing enormous damage to both plants and animals. Pathogenic oomycetes have huge economic impact in both wild and cultured ecosystems which has driven the focus of oomycete research mainly toward pathogenic species. Hence, the environmental studies of oomycetes, especially animal pathogenic oomycetes have been undermined. Animal pathogenic oomycetes, such as Saprolegnia species are destructive pathogens to many aquatic organisms and are found in most parts of the world. A number of Saprolegnia species e.g. S. delica, S. hypogyna, S. diclina were isolated from aquatic insects and amphipods and it was demonstrated that isolates of Saprolegnia from insects as well as known fish pathogens were highly pathogenic to eggs of Atlantic salmon (Salmo salar), nymphs of stoneflies (Perla bipunctata) and embryos of the African clawed frog (Xenopus laevis). Detailed light and scanning electron microscopy of the infected hosts revealed that Saprolegnia species form appressorium-like structures on selective hosts. It was found that a subset of papain like C1 Cysteine proteases in Saprolegnia parasitica were highly up regulated during infection of different hosts. Environmental sampling from different environments i.e. UK, the Falkland Islands and Antarctic Peninsula illustrated the diversity of oomycetes with as many as seven novel species being identified and characterised that belong to the genus Saprolegnia, Leptolegnia and Pythium in addition to many known species of oomycetes belonging to the families Saprolegniaceae and Pythiaceae. These results suggest that Saprolegnia spp. are capable of infecting multiple hosts, which may give them an advantage during seasonal variation in their natural environments. The results also suggest a model for infection of aquatic animals whereby both biochemical and mechanical force may be required to enter animal host cells. Furthermore, this thesis identifies and enlists novel as well as known oomycetes from different environments.

Thesis--University of Michigan, 1930. / "Paper from the Department of Botany of the University of Michigan, no. 321." "Reprinted from American journal of botany, vol. XVII, no. 6 ... June, 1930." "Literature cited": p. 542-544.

The success of eukaryotic oomycete pathogens depends largely on effector proteins, molecules that manipulate or interfere with host defence mechanisms in the extracellular space or inside their host cells. One economical important oomycete parasite is the fish pathogen Saprolegnia parasitica, which is the causal agent of saprolegniosis. S. parasitica is responsible for devastating losses in the aquaculture industry worldwide. In order to effectively fight S. parasitica it is crucial to understand its pathogenicity strategies. With the focus on cytoplasmic effector proteins, the genome of S. parasitica was screened in the present study for secreted proteins that possess Ricin-B-like lectin domains or potential N-terminal RxLR-motifs. A list of more than 30 potential effector candidates was compiled and gene expression analysis was performed with RNAseq. Possible functions of the candidate effectors are discussed. SPRG_21856.2 (Ricin-B-like lectin candidate) and SpHtp3 (RxLR candidate) were selected for further analysis. Although two different expression systems, Escherichia coli and Pichia pastoris, were used, recombinant protein production of SPRG_21856.2 was not successful. Possible reasons and alternative overexpression methods are discussed. For SpHtp3 recombinant protein production was successful. Functional characterisation revealed that SpHtp3 is an active nuclease capable of destroying both DNA and RNA molecules. Furthermore, SpHtp3 was found to specifically enter fish cells in an O-sulfate and pH-dependent manner. Interestingly, the potential N-terminal RxLR-motif of SpHtp3 was not required for translocation. In support of that finding also PsHtp3, a Phytophthora sojae homolog of SpHtp3 that lacks an RxLR-sequence, was capable of translocating into fish cells. After translocation SpHtp3 localised in small vesicles from which it was only released when the host cells were under direct attack by S. parasitica. SpHtp3 is the first protein described from an oomycete that exhibits both self-translocation and nuclease activities combined in one molecule. Potential functions and future applications are discussed.

This thesis aims to initially define the present knowledge of pathogens which infect algae, highlighting the potential economic significance of such pathogens, given the recent rise in algaculture. Focus is given to the oomycetes, a group of organisms which already contain several significant genera of plant (Phytophthora) and animal (Saprolegnia) pathogens, as well as Olpidiopsis; a genus reported to significantly impact algaculture in Asia. Subsequent chapters aim to genetically characterise stramenopiles (specifically oomycetes and hyphochytrids) associated with algae in two ways. Firstly known pathogens of algae, Olpidiopsis feldmanni and Anisolpidium rosenvingei are morphologically diagnosed by microscopy and genetically surveyed at phylogenetically significant loci. Further morphological information on these two pathogens is reported here expanding the current knowledge of these rarely reported organisms. Surprisingly, genetic evidence indicates that Anisolpidium, a uniflagellate genus, belongs to the biflagellate class Oomycota and not the closely related uniflagellate class Hyphochytriomycota, as previously suspected. Morphological and genetic features of these classes are contrasted to justify this molecular interpretation. These first two studies, along with the publically available sequences of algal pathogens are then used to design primers, which enable an oomycete-directed metagenomic survey of brown algae, allowing the investigation of what organisms are associated with these. At present the results of this survey are unreported. Finally a Eurychasma dicksonii transcriptome as well as genomic sequences of other stramenopiles are investigated for the presence of cadherin protein models. At present such models are automatically annotated and reported. This study is the first manual curation of the protein and defines a unique protein family which is presented by the oomycete genera Eurychasma, Pythium, Phytophthora and Albugo as well as the labyrinthulomycete Aurantiochytrium limanicum. The protein model is not reported from other sequenced oomycete genera or photosynthetic stramenopiles.

No description available.

Oomycetes are a class of organisms within which there are a range of devastating pathogens with a variety of different hosts including plants and animals. Phytophthora infestans, the causal agent of late blight in potato, is one of the most important plant pathogens in economical terms. Saprolegnia parasitica is a fish pathogenic oomycete capable of causing disease in freshwater fish species. This study uses both pathogens to work towards understanding the fundamental biology of oomycetes and the development of effective control strategies.

Differentiation and gene expression in the oomycete Achlya ambisexualis ( strain E87) were studied during three responses, sexual antheridium formation, asexual sporangium formation and heat shock. Polyacrylamide gel electrophoresis of proteins labelled in vivo and in cell free systems directed by poly(A) mRNA showed that during formation of antheridia only one change was detectable in the proteins synthesized. No detectable changes were observable in the translatable poly(A) RNA population indicating that post-translational events may be required for differentiation. During early sporangium formation several proteins showed changes in relative rates of synthesis. These correlate with similar changes in cell free translation products suggesting a transcriptional level of regulation. Nucleic acid hybridization analyses of mRNA populations indicated that many new sequences appear late and accumulate in the spore. These late transcripts are probably utilized during spore germination. During heat shock several proteins showed rapid increases in rates of synthesis; these seem to be controlled at the level of transcription.

Thesis (Ph. D.)--Ohio State University, 2003. / Title from first page of PDF file. Document formatted into pages; contains xiv, 156 p.; also includes graphics (some col.) Includes bibliographical references (p. 141-156). Available online via OhioLINK's ETD Center

Thesis (Ph.D.)--Aberdeen University, 2008. / Title from web page (viewed on March 9, 2009). Includes bibliographical references.