Taxonomic, ecological and biodegradation studies of the basidiomycetous wood inhabiting fungi of Karura forest –Kenya
Wood inhabiting basidiomycetous fungi are able to metabolise lignin, cellullose and hemicellullose components of the plant cell wall causing either a white rot when both lignin and cellullose are metabolized or a brown rot when only cellulose and hemicellulose are mineralized. White rot fungi are the major degraders of highly lignifiedtissue and so play an important role in the recycling of photosythetically fixed carbon. The lignin enzyme system of the white rot fungi is extracellular, non-specific and non-hydrolytic enabling these organisms to mineralize a varierty of synthetic insecticide compounds including polycyclic aromatics and some chlorinated phenols. These fungi can therefore, be useful in bio-remediation of contaminated soils as a result of pesticide use. Some wood inhabiting fungi are responsible for biodeterioration of timber in use and electric poles while others are pathogenic on living trees. The first critical flora. ef East Africa only treats the very important ecological aspects of the fungi peripherally. The enzyme system of the decay fungi has been studied mainly on one species, Phanerochaete chrysosporium. Since the system can be useful not only in bioremediation but also in biopulping, there is need for a comprehensive study of this system in other wood inhabiting fungi. This study therefore involved, taxonomic, ecological and biodegradation aspects of these fungi. The method ofRyvarden and Johansen (1980), Gilbertson and Ryvarden (1986) and Pegler (1977, 1984) were followed for taxonomic studies. The type of rot, host, rainfall,temperature, humidity and moisture were recorded when the forest was visited for a period of one year. Nitrogen and carbon were determined according to the method ofMerril and Cowling, (1966). The enzyme production and assays of P. luteoalbus were done following the method of Niku- paavola et al. (1988) with modification while DDT biodegradation studies were carried out using 14Cscintillation counter and GC analysis. The procedure of biodeterioration of timber followed Otjen and Blanshette (1987), 54 speciesbelonging to 35 genara were identified. Two new species of Diplomitoporus and Wolfiporia are proposed. The species Antrodia daedaliformis is transferred to genus Diplomitoporus frorrl Antrodia on the basis of decay characteristics. A new genus is proposed for Trametes elegans on the same grounds, while a revision is proposed for Schizopora and Favolus. A recombination of the genera Loweporus and Perreniporia is proposed The catalyticactivity of the ligninolytic enzyme~rele.ased by P. lutoalbus has A pHoptimum value of 4.0 and is substrate dependent with a KM value of 0.23 Ii molesand Vmax of0.357"fJ.molesper minute. This enzyme mineralised up to 69% 14C DDT to either 14C02or its metabolites while Pycnoporus sanguinerius caused up to 78% weight loss in Eucalyptus sp. Wood inhabiting basidiomycetes fruited at relativelylow water potential of - 20 to - 40 MPa and were affected by Carbon and Nitrogen independently but not by C:N ratio. Most fungi fruited at pH 5- 6. More fungi were added onto the East African Polypore Flora. Some species were reallocated to different genera and a new genus proposed based on decay characteristics. Pleurotus luteoalbus released enzymes comparable with those of Phanerochaete chrysosporium. The very efficient biodegradation of DDT by the above enzyme system proves the importance of these fungi in bioremediation and possiblybiopuling. The decay potential of Pycnoporus sanguinerius is quite high and suchknowledge is crucial in effective wood preservation .
Department of Botany, University of Nairobi
Doctor of Philosophy