P. boydii - model for the evolution of opportunistic fungi

Medical microbiologists are confronted with an increasing number of infections due to opportunistic fungi: opportunistc fungal infections are supported by the continous increase of susceptible individuals. Nevertheless a certain degree of virulence has to exist in a species or strain to persist in tissue and cause diseases. P. boydii, one of the emerging agents of diverse opportunistic mycosis, is isolated frequently from sources with low oxygen and high nutrient availability, i. e. intensive-agricultural soils and drainage ditches. Those eutrophic habitats could serve as reservoires for those agents. We want to explore the effect of human activities, manifested as an abundant supply with N-and P-sources, on the evolution of P. boydii. P. boydii is suspected to go through a process of development of strains with higher virulence. Work on the following questions should elucidate the biology and systematics of P. boydii and allow conclusions on the evolution of opportunists in general: 1) Is P. boydii a homothallic species or do different mating types exist? 2) If there are mating types, do they correlate with intraspecific clustering based on ITS-sequences and nDNA/DNA reassociation? 3) Does the concentration of anthropogen N- and P-sources have an influence on the competition between strains? 4) Does the concentration of anthropogen N- and P-sources have an influence on the mode of reproduction (clonal vs. recombination) of certain strains? Experimental steps will be: 1) evaluation of homo- or heterothallic reproduction with mating experiments, 2) proof of recombination frequency via molecular typing methods, 3) delineation of intraspecific groups with the help of mating experiments and already gained molecular data, 4) differences between human and environmental strains concerning the utilisationolerance of N- and P-sources and possible competition and selection between them with the help of liquid cultures and molecular typing methods, 5) development of a FISH-system for known strains with the help of sequencing, 6) evaluation of the favouring of a certain reproduction mode (clonal vs. recombination) derived from previously produced data. The gained informations can help to deepen the understanding of the evolution of opportunistic fungi in general. As extensive molecular data already exist, P. boydii promises to be a potent model. Additionally the proposed study is embedded in an ECMM-network and will contribute to a proposed EU-project (6 th framework programme for research) coordinated by Prof. Dr. G. S. de Hoog (CBS, NL).

Opportunistic pathogenic fungi are recognised as cause of severe infections with increasing frequency due to the rising number of risk patients. Pseudallescheria boydii is one of those and is even able to infect otherwise healthy persons. It is known as agent of diverse clinical pictures and resistant to most of the available antifungal drugs. The infections occur mostly as traumatic inoculations after e. g. motorbike accidents or as a result of the aspiration of contaminated water after near drowning events. The ecological niche is assumed to be nutrient rich, eutrophic habitats. Research in this project aimed to describe anthropogenic factors, which could promote the distribution of P. boydii and have an influence on the development of populations. Further, molecular changes and reproduction modes were investigated for a better understanding of the biology and evolution of opportunistic pathogens. The most important results were: 1) P. boydii is a species complex and not a single species. This is important, because the complex behaviour as pathogen and strain dependent resistance to drugs could be understood better. 2) Tolerance to Nitrogen and Phosphate sources is strain dependent in P. boydii. 3) P. boydii has a high competitive potential under nutrient rich conditions. 4) Among the tested P. boydii strains some were more competitive than others. Selection was not only strain dependent but was also down to the applied nutrient sources. 5) Competitive effects were amplified by higher temperatures. 6) Even though P. boydii is an ascomycete, reproduction occurs mainly clonal, also in sexual reproduction organs. The most important outcome of the project was, that we were able to describe the effect of certain anthropogenic influences on populations and communities in detail. This results can be used for computer models on risk assessment of environmental changes.