Wood-Decomposing Fungi: Soil colonization, effects on indigenous bacterial community in soil and hydroxyl radical production

University dissertation from Microbial Ecology, Ecology building, S-22362 Lund, Sweden

Abstract: The extracellular enzyme activities of wood-decomposing basidiomycetes are essential for wood degradation, but are also able to degrade various recalcitrant organic pollutants. The possible application of wood-decomposing fungi in bioremediation has increased the interest in understanding their growth and activity in soil. Degradation and mineralization of pollutants can also be influenced by synergistic and antagonistic interactions between microorganisms. In this work I have shown that inoculation of soil with wood-decomposing fungi changes the indigenous bacterial community in the soil by analysing the phospholipid fatty acid (PLFA) pattern. Rather constant differences in bacterial PLFA composition were also found between the different fungal species within experiments. White-rot fungus Pleurotus ostreatus had a marked negative effect on the amount of bacterial PLFAs and colony forming units, which was accompanied by slower degradation of some PAHs and an accumulation of PAH metabolites in soil. Of thirty-two fungal species, which were investigated for soil colonization ability, less than ten species colonized the soil well. However, there are often shortcomings in, or a lack of techniques for studies of fungal growth in soil. Therefore, a method was developed, which could monitor colonization of wood-decomposing bacteria in three dimensions in soil, taking advantage of the ability of wood-decomposing fungi to colonize wood. The method, which was based on selective plating and molecular identification techniques, was used to monitor the growing mycelium of the brown-rot fungus Antrodia vaillantii in a non-sterile soil in a laboratory soil microcosm. A method for studying hydroxyl radical production by wood-decomposing fungi was also developed. This method was based on the specific reaction between coumarin-3-carboxylic and hydroxyl radicals, which produces a fluorescent product. The method was applied to fungi growing on agar plates. Hydroxyl radical production was demonstrated by both brown- and white-rot fungi. Interactions between wood-decomposing fungi and bacteria resulted in species-specific increases in hydroxyl radical production. Interactions between different fungal species changed the spatial distribution of hydroxyl radical production, in a way that was also specific for the different combinations of species.

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