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The effects of two extraction procedures on the yield and properties of APPL (acid-precipitable polymeric lignin, or solubilized lignocellulose) produced by four streptomycetes during growth in solid-state fermentation were examined. When APPL was extracted with NaOH (0.1 M) rather than distilled water, y i e Ids increased threefold, with Streptomyces cha ttanoogensis exhibiting maximum solubilization levels [I63 mg product (g straw) '']. Alterations in the characteristics of APPL obtained during extraction with NaOH were detected using cross-polarization and magic-angle spinning (CPMAS) 13C NMR and IR spectroscopy and by GC-MS analysis after CuO oxidation, with the most significant changes detected in the cinnamic acid and lignin moieties. When APPL was extracted with NaOH, ester links between hemicellulose and lignin and between hemicellulose and cinnamic acid were cleaved, resulting in a decrease in the alkyl and carbonyl groups attached to lignin, enabling greater solubilization. Yields of APPL extracted with water were lower, but spectral characterization of this APPL suggested a possible role for actinomycete peroxidases and phenolic acid esterases in lignin solubilization. For industrial solubilization of lignocellulose, a possible role for the application of streptomycetes, or their enzymes, in alkali extraction is suggested as a means of increasing solubilization levels.Keywords : streptomycetes, acid-precipitable polymeric lignin, lignocellulose degradation INTRODUCTIONThere is considerable interest in the biological degradation of lignocellulose in the environment and its potential for industrial application. The biotechnological potential of waste biomass bioconversion has centred upon the biological and chemical treatment of lignocellulosic material to produce a range of products, including ethanol and sugars (Hartley et al., 1987). Also, the transformation of wheat straw during the growth of micro-organisms under solid-state fermentation conditions has been examined for the upgrading of straw to produce pulps and animal feed (for a review see Dart & Betts, 1991). The potential role of lignocellulosedegrading enzymes in the bleaching of pulp for paper has been investigated as an alternative or supplement to chemical bleaching techniques, which cause environmental problems through the release of chlorinecontaining effluents. Among the micro-organisms screened for the production of suitable enzymes, the actinomycetes are a group that have often been selected (Winter et al., 1991;Zhou et al., 1993).Actinomycetes produce a range of hydrolytic and oxidative enzymes which act co-operatively in degradation of the lignocellulose complex during primary growth (Ball et al., 1990). The mechanisms involved in this degradation process have not yet been fully elucidated; however, the main role attributed to these micro- organisms is solubilization rather than depolymerization and mineralization of lignin (McCarthy, 1987). The main product of solubilization of wheat straw and other lignocellulosic residues by act...

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Low molecular weight aromatic compounds released during the growth of several Streptomyces strains on wheat straw in solid-state fermentation (SSF) were identified by gas chromatography/mass spectrometry. The analysis of the compounds derived from p-hydroxyphenyl, guaiacyl and syringyl units (H, G and S respectively) of lignin indicate the ability of streptomycetes to depolymerize lignin from lignocellulose substrates. Differences in the relative area of the compounds obtained from fermented substrate from the uninoculated control were observed. Moreover, the different proportion of the aromatic compounds obtained from fermented wheat straw proved that the ability to depolymerize lignin in Streptomyces is strain specific. The predominance of acidic forms among these compounds showed an oxidative attack on lignin by Streptomyces. The high level of vanillic acid released from lignin by the strains Streptomyces UAH 23 and Streptomyces UAH 33 seems to indicate the breakdown of Ca-Cb linkages in the lignin molecule. The biotechnological applications of ferulic and vanillic acid as precursors of food additives is also undertaken.