Oleg Milstein

Partial suppression of cellulase action by artificial lignification of cellulose

Abstract Lignocellulose from plants is the major organic material in the biosphere and it is slowly biodegraded. The inability of cellulases to degrade the cellulose in the natural complex with lignin could be due to cellulose crystallinity or to a steric hindrance or other factors from the lignin. Digestible cellulose was artificially lignified using peroxidase, H2O2 and eugenol. It was less degradable by cellulases and by Trichoderma suggesting that it is the complexed lignin that interferes with cellulose degradation.

Metabolism of lignin related aromatic compounds by Aspergillus japonicus

Aspergillus japonicus metabolizes a wide variety of aromatic compounds, some of them resulting from lignin degradation. The efficient conversion of such compounds is related to the efficiency shown by this fungus in degrading the aromatic portion of lignocarbohydrate complexes. The rate and extent of degradation of simpler aromatics is affected by cellobiose which enhances their degradation but there are examples in which it is inhibitory. The organism was capable of the following activities: Non-oxidative and oxidative decarboxylations, aromatic alcohol and aldehyde oxidation, aromatic acid reduction, side chain oxidation, demethylation of aromatic compounds, aromatic ring hydroxylation and aromatic ring cleavage. A scheme is shown for the biodegradative pathways of phenylpropanoids and derived compounds in A. japonicus. This versatile fungus seems to have more rapid rates and a wider spectrum of biodegradative activities than other fungi previously tested.

Biodegradation of wheat straw lignocarbohydrate complexes (LCC)

SummaryHot water extractions of ground wheat straw were performed as part of a study to assess digestibility and utility as a substrate for ligninolytic fungi. The treatments gave solutions containing phenolics and carbohydrates. After 48 h reflux percolation or 3 h autoclaving, little additional carbohydrates or phenolics were extracted into the liquors. During percolation, the pH of the wet straw in the reflux thimble fell only slightly and it is difficult to attribute the extraction in this case to an autohydrolytic process catalyzed by organic acids liberated from the straw.Gel permeation chromatography enabled the separation of the extracts into fractions, several of which were free of reducing sugars but contained phenolics and bound carbohydrates. Rechromatography of these fractions failed to separate these two components, indicating a tight linkage between them. The bound sugars were identified as glucose, arabinose, xylose and traces of galactose, but uronic acids were absent. The high molecular size fraction was rich in glucose whereas lower molecular size fractions were richer in xylose and arabinose and poor in glucose.

Solar pasteurization of straw for nutritional upgrading and as substrate for ligninolytic organisms

SummarySolar digesters were designed to wet pasteurize straw. Microbial levels were reduced, precluding competition with ligninolytic organisms. The pasteurization treatment alone increased the available cellulose by 20–40%. Ligninolytic organisms produced biomass with 6–8% protein on pasteurized wheat straw.

Rapid, Sensitive, and Inexpensive Assay for the Determination of Lignin Degradation Using Different Flourescence Labelled Lignin Derivatives

Until now alarge scale screening oflignin degrading microorganisms is hardly possible because the process of lignin degradation still is very difficult to monitor under laboratory conditions. Several methods for analysis of lignin decay are worked out until now. The first approach to the decay of lignin äs it can be observed in natural wood was done by microscopical techniques (Meier 1955). Hiroi and Eriksson (1976) cultivated lignin degrading organisms on solid medium (agar, silica gel) containing milled-wood lignin or kraft lignin using the chlorine number method (Kyrklund and Strandeil 1967) äs a function for lignin content. This is a laborious and rather insensitive assay for lignin decay considering merely the loss of lignin and not the emerge of degradation products.

Lignin degrading ability of selected aspergillus Spp.

AbstractMost lignin research has been on wood-rot fungi and not on other lignolytic organisms. Members of the genusAspergillus inhabit lignin-rich environments, and we have studied their relative lignin-degrading potential.Aspergillus fumigatus, A. japonicus, A. niger, andA. terreus were tested for their ability to metabolize14C-labeled aromatic compounds. The species tested decarboxylated, demethoxylated, and cleaved the rings of coumaric, ferulic, vanillic, veratric, and anisic acids. More than 90% of C-ring-labeled ferulic and vanillic acids disappeared from the medium in 96 h of cultivation. More than half of the above was respired, the rest was incorporated in unknown form into the mycelium. Mycelia were homogenized and about 3% of the initial label was found in TCA precipitate of the cell-free supernatant. Protocatechuic acid 3,4-dioxygenase (EC 1.13.11.3) and catechol 1,2-dioxygenase (EC 1.13.11.1) activities were detected in the mycelial extracts of theAspergillus spp.All theAspergillus spp. were capable of degrading both aromatic and carbohydrate components of water-soluble lignocarbohydrate complexes (LCC) from wheat straw. The degradation of the aromatic moiety of soluble LCC with apparent molecular mass more than 100,000 daltons was far more active in theAspergillus spp. than in the whiterot fungi tested; i.e.Polyporus versicolor, Pleurotus ostreatus, andForties annosus. The aromatics present in the soluble LCC, as well as a variety of lignin-related compounds tested, did not affect the production of hemicellulases byA. japonicus. Aspergillus spp. degraded14C-dehydrogenative polymerizates, converting carbon from the ring as well as from the -O14CH3 groups to14CCO2.14CO2 release after 21 d did not exceed 10% of the total14C input. This situation is comparable to some white-rot fungi. Lignosulfonate was poorly degraded byA. japonicus, but clearly modified.Fomes annosus was able to grow much better on lignosulfonate whenA. japonicus had previously grown on it.Aspergillus spp. grew efficiently on wheat straw, utilizing lignin and some carbohydrates, and rendering the remaining carbohydrates more available to attack of carbohydrases.