Development and comparison of methods for measuring growth of filamentous fungi on wood

Abstract

Measures of fungal growth with potential for use on wood-chip media were developed. These included (i) visual inspection, (ii) substrate dry weight loss, (iii) rate of fluorescein diacetate hydrolysis, (iv) extractable protein content, and (v) chitin content of the colonized substrate. The responses of the various assays to different growing conditions were assessed by using them on measured weights of mycelium, collected at intervals from liquid media with various composition. Growth of various species on either nutrient supplemented or unsupplemented wood chips was then measured. Each assay measured a different aspect of growth. The relationship between these changed in a distinctive way for each species during growth. Chitin gave the best measure of biomass, whereas fluorescein diacetate hydrolysis was a measure of growth-related metabolic activity. The protein and substrate dry weight loss data gave information about fungal protein and carbohydrate metabolism of the species, respectively. Addition of nutrient supplement to the wood increased both biomass and growth-related metabolic activity. It also increased the amount of wood used to produce a given amount of biomass by about 500% with some species. Some species showed a strong capacity to lower their cellular protein concentration during growth, which is probably of advantage for growth on a low-N substrate such as wood. Used together, the assays gave insight into different strategies fungi use to grow on wood. Key words: fungi, growth, chitin, fluorescein diacetate.