Extracellular Enzyme Production and Wood Degradation by Freshwater Lignicolous Fungi
Zare-Maivan, Hassan
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https://hdl.handle.net/2142/71288
Description
Title
Extracellular Enzyme Production and Wood Degradation by Freshwater Lignicolous Fungi
Author(s)
Zare-Maivan, Hassan
Issue Date
1987
Doctoral Committee Chair(s)
Shearer, Carol Anne
Department of Study
Plant Biology
Discipline
Plant Biology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Botany
Biology, Ecology
Abstract
In terrestrial habitats, fungi, especially white- and brown-rot fungi, are important decomposers of wood. It is not known, however, whether fungi play a comparable role in freshwater systems. Although numerous fungal species have been reported from submerged wood, little is known about their degradative activities. This study was undertaken to determine for selected species of freshwater wood-inhabiting ascomycetes, hyphomycetes and an oomycete: (1) the range of plant components that they are able to hydrolyze; (2) whether they are able to degrade cell walls of woody tissue; (3) the extent to which they degrade specific wood components such as cellulose, hemicellulose, and lignin; and (4) the effect of wood type on their degradation activities.
Extracellular enzymes were assayed on both solid and liquid media. Type of cell wall degradation was determined by growing fungi on thin-sections of ash and cottonwood, and then examining colonized sections with polarized light. Wood decay activity was determined by growing fungi on small wood and bark blocks of ash and cottonwood, and measuring weight-loss of the blocks after incubation. Analytical measurements of changes in cell wall components were determined chemically according to TAPPI standard methods.
Except for Pythium sp., all species produced a broad array of extracellular enzymes. The greatest differences in enzyme production among species were for pectinases, laccase, tyrosinase, gum guaiac oxidase, oxidases for lignin derivatives, and chitinase. Pyramidospora sp. was positive for all enzymes tested and caused the highest weight-loss in ash and cottonwood blocks. This species and Pseudohalonectria lignicola, Pseudohalonectria sp. 1, and Trichocladium lignincola were the most active degraders of cell walls and produced laccase and hydrolyzed lignin derivatives. Although the early-successional species, Nectria haematococca, N. lucidum, Filosporella annelidica, Heliscus lugdunensis, and Pythium sp., produced coupled cellulases, they did not degrade lignin derivatives, form soft-rot cavities or cause much weight-loss in wood test blocks. Inability to degrade intact cell walls and lignin may contribute to their early disappearance from wood.
Cottonwood was degraded more rapidly and to a greater extent than ash. Weight-loss in bark blocks was generally greater than in sapwood blocks. The inner bark was colonized by more species and degraded more than the outer bark.
Species able to degrade wood produced typical soft-rot cavities and caused slow, superficial degradation of wood. No species were found to be very active decomposers or to cause the type of degradation characteristic of terrestrial white- and brown-rot fungi.
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