Biodegradation of wheat straw lignocarbohydrate complexes (LCC)

Performance of wood-rotting fungi-based enzymes on enzymic saccharification of rice straw

BACKGROUND

For effective saccharification of rice straw we focused on enzyme preparations from wood-rotting fungi that have the ability to degrade cell wall polysaccharides and lignin. We tested extracellular enzyme preparations from 14 species of fungi for saccharification activity and examined the factor for saccharification by statistical analysis.

RESULTS

An enzyme preparation from Schizophyllum commune had the highest saccharification activity of rice straw. This preparation contained highly active endo-β-xylanase, endo-β-glucanase (CMCase), β-d-glucosidase and acetylxylan esterase. Correlation analysis of the 14 enzyme preparations demonstrated that acetylxylan esterase was closely related to saccharification activity in rice straw. Multiple regression analysis also showed that acetylxylan esterase had an important role in saccharification. Ligninolytic enzymes, which are characteristic of white-rot fungi, did not contribute to saccharification activity of rice straw.

CONCLUSION

Deacetylation is an essential factor for saccharification of rice straw and enzyme preparations for saccharification need to contain highly active acetylxylan esterase as well as highly active cellulolytic and xylanolytic enzymes, but not ligninolytic ones.

Biological bleaching of chemical pulps: A review

The pulp and paper industry is implementing changes in the bleaching process to minimize the use of chlorine in order to satisfy regulatory and market demands. Biotechnology has a potentially important role to play in providing alternatives to conventional chlorine bleaching of chemical pulps. The current developments in fungal, enzymatic and biomimetic bleaching are reviewed here within an engineering context.

Degradation of Lignin by Cyathus Species

The ability of 12 Cyathus species to degrade 14 C-labeled lignin in kenaf was studied. The sum of 14 C released into solution plus 14 C released into the gas phase over a 32-day fermentation period was used to determine average daily rates of lignin biodegradation. Cyathus pallidus. C. africanus , and C. berkeleyanus delignified kenaf most rapidly. C. canna showed the greatest preference for lignin degradation over other plant components, and its rate of lignin degradation was only slightly lower than the three most active species. The apparent ability of fungi to metabolize low-molecular-weight lignin breakdown products correlated well with their overall delignification rates. C. stercoreus metabolized degradation products of lignin from wheat straw better than those from kenaf lignin, based on the amount of low-molecular-weight products left in solution.

Fungal Biodegradation and Biotransformation of Soluble Lignocarbohydrate Complexes from Straw

Aspergillus japonicus is an efficient degrader of phenolics and carbohydrates present in a mixture of soluble lignocarbohydrate complexes extracted from wheat straw. Trichoderma sp. attacked part of the carbohydrate but hardly affected the aromatic portion of this solution. Polyporus versicolor had a complex effect; polymerization of low-molecular-size phenolics accompanied the degradation of aromatic and carbohydrate polymers. The addition of xylose to the medium facilitated depolymerization of lignin by the fungi tested and prevented the polymerization of low-molecular-size fractions of lignocarbohydrate complexes by P. versicolor. P. versicolor , in contrast to A. japonicus and Trichoderma sp., also excreted into the medium considerable amounts of laccase, but only in the absence of endogenous or exogenous carbohydrates. Apparently, laccase is involved in polymerization rather than degradation of lignin in this organism. A number of extracellular glycanases were also secreted by these fungi.