Abstract
Lignocellulose degradation is being explored as part of the process of bioethanol production from waste products, such as wood-flour. Identified as a natural lignin degrader and its ability to produce cellulase enzymes, Streptomyces viridosporus was deemed worthy of investigation for lignocellulose degradation. It has the ability to degrade lignin, hemicellulose and cellulose components of lignocellulose substrates by secreting a large range of lignocellulose degrading enzymes, including peroxidases, esterases, endoglucanases and xylanases. Experiments in other laboratories had show that this Streptomyces species is capable of degrading both hard- and soft- wood substrates, as well as grass lignin lignocellulose. Using a continuous (chemostat) culture and employing carboxymethylcellulose (CMC) as the main carbon source, five dilution rates were investigated (0. 05h-1, 0. 07b-1, 0. 09h-1, 0. 11h-1 and 0. 13h-1) and the effect of mycelium taken from steady state cultures, on the lignocellulose degradation of wood-flour by S. viridosporus analysed. Employing in vivo and in vitro techniques the complex relationship between lignocellulose components and cellulase enzymes were investigated, as well as the effects of amino acids and nutrient limitations on cellulase activity. In particular, a critical sequence of enzyme activity and precursor liberation for successful degradation to glucose was identified. We have obtained conditions whereby S. viridosporus can successfully degrade lignocellulose, without using all the liberated sugars as a carbon source. Liquid cultures of S. viridosporus were able to liberate glucose from wood-flour (mesh size 40). This finding indicated considerable potential for using this species in lignocellulose degradation for commercial exploitation (as a precursor to bioethanol production). However, S. viridosporus liquid cultures have a pre-disposition to form pellets (discrete islands of hyphal growth) which can inhibit the effectiveness of some hyphal species in biotechnological processes (such as antibiotic biosynthesis). The pelleting of cultures was reduced by the selection of a non- pelleting strain via a prolonged continuous culture.