Biodegradation of the wood Ceriporiopsis subvermispora: characterization of residual polymers

Author(s)

Anderson de Almeida Guerra

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Conjunto das Químicas (IQ e FCF) (CQ/DBDCQ)
• Defense date: 2002-05-27

Examining board members

André Luís Ferraz; Adalberto Pessoa Junior; Luiz Pereira Ramos; Flávio Teixeira da Silva; Michele Vitolo

• Advisor: André Luís Ferraz

Abstract

Biopulping is the fungaI pretreatment of wood chips designed as a solid-state fermentation process for production of mechanical or chemical pulps. Although promising results have been obtained by combining fungaI pretreatment with chemical pulping methods, there is no relationship between the pattern of biodegradation of the wood components and the increase in efficiency of pulp methods subsequently adopted. This study presents some efforts to elucidate changes in the structure of residual components and enzymes produced during the wood biotreatment. Softwood Pinus taeda was degraded by Ceriporiopsis subvermispora for periods from 15 to 90 days under solid-state fermentation. The fungus degraded lignin and extractives extensively without removing large amounts of glucan. Polyoses were significantly removed (7%) only after 60 days of degradation, reaching 31 % after 90 days . Decayed and undecayed wood chips were characterized as to their residual lignin and polysaccharides. Residual lignin fraction was evaluated by using in situ techniques and analysis performed on milled wood lignin and enzymatically-liberated lignin isolated from biodegraded wood. Compiled data suggested that the main reaction taking place on the lignin moiety during biodegradation was the cleavage of β-0-4 linkages. This oxidation reaction generates lignin depolymerization, which is followed by an increase in the amount of dimmers connected by C-C and 4-0-5 linkages and the appearance of new saturated-carbons at the side chain. After longer biodegradation periods, ring-opening reactions can also occur. Depolymerization of cellulose was evaluated by preparing α-cellulose samples from biotreated wood chips. High performance size exclusion chromatography of tricarbanyl derivatives of these α-cellulose samples was also evaluated. Both, acellulose yield and elution profiles indicated some depolymerization of the cellulose fraction starting from the 30th day of biodegradation. This result suggests that degradation reactions started at the cellulose backbone before mineralization has been detected as glucan loss. Hydrolytic and ligninolytic enzymes were extracted from the cultures and quantified.· During the first 30 days of biodegradation, high xylanolytic activities did not produce an extensive degradation of the polyoses fractions indicating that the biodegradation process was limited by the low porosity of the wood ceIl walls. On the other hand, some enzimatically-mediated reactions are suggested to be responsible for cellulose and lignin depolymerization at an early decay stage. (AU)