Screening of white-rot fungi on (14C)lignin-labelled and (14C)whole-labelled wheat straw

Summary 74 Basidiomycetes have been tested for ligninolytic capability on (¹⁴C)lignin-labelled wheat straw. Fifteen strains were selected and rested more accurately for ligninolytic activity and the capacity to degrade wheat straw. The asymptote, inflexion point and degradation rate were determined using a model approach. The fungi exhibited very different responses with respect to lignin biodegradation: high asymptote for Pleurotus ostreatus (77%), low inflexion points for Sporotrichum pulverulentum Nov. (6.1 days) and Pycnoporus spp. (2.7 to 4.7 days) with high and slow degradation rates, respectively (0.91% and 0.45% of ¹⁴CO₂ release/day). Degradation values for (¹⁴C)whole-labelled wheat straw exhibited less variation. Finally, the strains Pleurotus ostreatus, Dichomitus squalens and Bjerkandera adusta showed the highest selectivity of lignin removal.     

Solid state fermentation of lignocellulose containing plant residues withSporotrichum pulverulentum Nov. andDichomitus squalens (Karst.) Reid.

Summary The fermentation profiles ofSporotrichum pulverulentum andDichomitus squalens showed distinct differences.D. squalens digested the substrate more slowly thanSporotrichum pulverulentum. The relative degradation rates of total organic matter and lignin also differed considerably.Whereas withS. pulverulentum the ratio was about the same throughout the whole observation period, withDichomitus squalens it altered in favour of lignin degradation.WithSporotrichum pulverulentum an optimum digestion in vitro of 40%–50% was achieved after 20 days of incubation. WithDichomitus squalens the best value (about 60%) was reached after 30 days of incubation. Increasing incubation temperatures enhanced the degradation of the substrate.As found with wheat straw, all other substrates tested (straw of rape and barley, glumes of rice) were degraded more slowly byDichomitus squalens than bySporotrichum pulverulentum. The degradation rates for oak, spruce and beech sawdust were very low compared to those for straw.Small amounts of ammonium nitrate stimulated the degradation of straw byS. pulverulentum whereas higher concentrations had an inhibitory effect. The optimum water content of the substrate, measured by decomposition of total organic matter and lignin and by in vitro digestibility, was between 50 and 100 ml of water/25 g substrate. Higher and lower water contents had an unfavourable effect.Varying the pore size of the substrate by using milled straw of defined particle size had no influence on the 6 parameters tested under the given experimental conditions.The best method to supress potential competitors was to heat the substrate to 90°C for 24 h.     

Screening of white-rot fungi for their ability to mineralize polycyclic aromatic hydrocarbons in soil

Soil samples from an agricultural field contaminated with 10 ppm¹⁴C-benz(a)anthracene in glass tubes were brought into contact with cultures of wood-rotting fungi, precultivated on wheat straw substrate. Forty-five strains of white-rot fungi and four brown-rot fungi were tested for their ability to colonize the soil and to mineralize¹⁴C-benz(a)anthracene to¹⁴CO₂ within a 20-week incubation time. Twenty-two white-rot fungi and all brown-rot fungi were unable to colonize the soil. Twenty-three strains of white-rot fungi, all belonging to the genusPleurotus, colonized the soil. During the experiment the noncolonizing fungi and their substrate disintegrated more and more to a nonstructured pulp from which water diffused into the soil. The same phenomenon was observed in the control which contained only straw without fungus and contaminated soil. In samples with colonizing fungi the substrate as well as the mycelia in the soil remained visibly unchanged during the entire experiment. Surprisingly, most samples with fungi not colonizing the soil and the control without fungus liberated between 40 and 58 % of the applied radioactivity as¹⁴CO₂ whereas the samples with the colonizing fungi respired only 15–25 % as¹⁴CO₂. This was 3–5 times more¹⁴CO₂ than that liberated from the control (4.9 %) which contained only contaminated soil without straw and fungus. A similar result was obtained with selected colonizing and noncolonizing fungi and soil contaminated with 10 ppm¹⁴C-pyrene. However, in pure culture studies in which¹⁴C-pyrene was added to the straw substrate,Pleurotus sp. (P2), as a representative of the colonizing fungi, mineralized 40.3 % of the added radioactivity to¹⁴CO₂. The noncolonizing fungiDichomitus squalens andFlammulina velutipes liberated only 17.2 or 1.7 %, respectively, as¹⁴CO₂. These results lead to the hypothesis that the native soil microflora stimulated by the formed products of straw lysis is responsible for high degradation rates found with noncolonizing fungi.     

Two-step degradation of pyrene by white-rot fungi and soil microorganisms

  The effect of soil microorganisms on mineralization of ¹⁴C-labelled pyrene by white-rot fungi in solid-state fermentation was investigated. Two strains of white-rot fungi, Dichomitus squalens and a Pleurotus sp., were tested. The fungi were incubated on milled wheat straw contaminated with [¹⁴C]pyrene for 15 weeks. CO₂ and ¹⁴CO₂ liberated from the cultures were determined weekly. To study the effect of soil microorganisms on respiration and [¹⁴C]pyrene mineralization in different periods of fungal development, the fungal substrate was covered with soil at different times of incubation (after 0, 1, 3, 5, 7, 9 or 11 weeks). The two fungi showed contrasting ecological behaviour in competition with the soil microflora. Pleurotus sp. was highly resistant to microbial attack and had the ability to penetrate the soil. D. squalens was less competitive and did not colonize the soil. The resistance of the fungus was dependent on the duration of fungal preincubation. Mineralization of [¹⁴C]pyrene by mixed cultures of D. squalens and soil microorganisms was higher than by the fungus or the soil microflora alone when soil was added after 3 weeks of incubation or later. With Pleurotus sp., the mineralization of [¹⁴C]pyrene was enhanced by the soil microflora irrespective of the time of soil application. With D. squalens, which in pure culture mineralized less [¹⁴C]pyrene than did Pleurotus sp., the increase of [¹⁴C]pyrene mineralization caused by soil application was higher than with Pleurotus sp. Received: 8 March 1996 / Received revision: 1 July 1996 / Accepted: 8 July 1996     

Influence of cell immobilization on the production of benzaldehyde and benzyl alcohol by the white-rot fungi Bjerkandera adusta, Ischnoderma benzoinum and Dichomitus squalens

Three white-rot basidiomycetes, Bjerkandera adusta, Ischnoderma benzoinum and Dichomitus squalens, were cultivated on a liquid medium supplemented with l-phenylalanine, a precursor for benzaldehyde (bitter almond aroma) and benzyl alcohol. Remarkable amounts of benzaldehyde (587 mg l⁻¹) were found in cultures of B. adusta. Immobilization of this fungus on polyurethane foam cubes allowed an 8.3-fold increase of the production of benzaldehyde and a 15-fold increase of the productivity as compared with non-immobilized cells. Aryl-alcohol oxidase activity was only detected in B. adusta. This activity was also significantly enhanced in immobilized cells, suggesting that it plays an important role in benzaldehyde biosynthesis. Conversely, consistent amounts of benzyl alcohol (340 mg l⁻¹ for B. adusta and I. benzoinum and 100 mg l⁻¹ for D. squalens) were produced by the three fungi when immobilized. Laccase activity was found only in the strains I. benzoinum and D. squalens. This activity was markedly enhanced in free cells cultures. Immobilization of the fungi did not promote benzyl alcohol production by comparison with free cell cultures (500 mg l⁻¹). Received: 10 December 1996 / Received revision: 17 February 1997 / Accepted: 22 February 1997     

Modification of wheat straw lignin by solid state fermentation with white-rot fungi

The potential of crude enzyme extracts, obtained from solid state cultivation of four white-rot fungi (Trametes versicolor, Bjerkandera adusta, Ganoderma applanatum and Phlebia rufa), was exploited to modify wheat straw cell wall. At different fermentation times, manganese-dependent peroxidase (MnP), lignin peroxidase (LiP), laccase, carboxymethylcellulase (CMCase), avicelase, xylanase and feruloyl esterase activities were screened and the content of lignin as well as hydroxycinnamic acids in fermented straw were determined. All fungi secreted feruloyl esterase while LiP was only detected in crude extracts from B. adusta. Since no significant differences (P > 0.05) were observed in remaining lignin content of fermented straw, LiP activity was not a limiting factor of enzymatic lignin removal process. The levels of esterified hydroxycinnamic acids degradation were considerably higher than previous reports with lignocellulosic biomass. The data show that P. rufa, may be considered for more specific studies as higher ferulic and p-coumaric acids degradation was observed for earlier incubation times.     

Inheritance of cellulose- and lignin-degrading ability as well as endoglucanase isozyme pattern in Dichomitus squalens

Summary The progeny of Dichomitus squalens CBS-432-34 is heterogeneous with respect to specific growth rate on glucose, cellulolytic ([U¹⁴C]cellulose ¹⁴CO₂) and ligninolytic ([¹⁴C]synthetic lignin ¹⁴CO₂) activities with little correlation between these metric characters. Variations do not show clear-cut phenotypes but rather a continuous range between extreme values pointing to multigenic control of these characters. Most homocaryons showed decreased cellulolytic or ligninolytic activity compared to the parent dicaryon. However a few homocaryons were comparable or even superior to the parent dicaryon for ligninolytic or cellulolytic activity with no correlation between each factor. Strains with reduced cellulolytic activity and altered isozyme patterns of endoglucanases were isolated in the progeny of D. squalens CBS-432-34. While the parent strain produced three main endoglucanase multiple enzymes designated EnI, EnII and EnIII, several strains in the progeny produced a different multiple enzyme pattern. In contrast to the quantitative ability to degrade cellulose, multiple enzyme pattern variation in the progeny did not show continuous variations. characterization of heterocaryon phenotypes derived from Ien⁺ and Ien 1 homocaryons and first filial generation (f1) analysis showed that genetic control of the multiple enzyme pattern (Ien 1 phenotype) in D. squalens is complex. Offprint requests to: E. Odier     

Degradation of styrene by white-rot fungi

Degradation of styrene in the gaseous phase was investigated for white-rot fungi Pleurotus ostreatus (two strains), Trametes versicolor, Bjerkandera adusta and Phanerochaete chrysosporium. Fungi were grown in liquid culture and the gas/mycelium contact surface was enhanced with the help of perlite. The influence of various inducers on styrene degradation was studied. The best inducers for styrene degradation were lignosulphonate for P. ostreatus and T. versicolor and wood meal for B. adusta and P. chrysosoporium. Under these conditions all fungi were able to degrade styrene almost completely in 48 h at a concentration of 44 μmol/250 ml total culture volume; one strain of P. ostreatus was able to remove 88 μmol styrene under these conditions. Three transformation products of [¹⁴C]styrene in cultures of P. ostreatus were identified: phenyl-1,2-ethanediol, 2-phenylethanol and benzoic acid; 4% of the styrene was metabolised to CO₂ in 24 h and no other volatile products were found. Received: 16 July 1996 / Received revision: 23 September 1996 / Accepted: 29 September 1996     

Degradation of 14C-labelled poplar wood lignin by selected white-rot fungi

Summary Of eight white-rot fungi examined, seven fungi grew on nitrogen-limited poplar wood meal medium and degraded ¹⁴C-lignin in wood meal to ¹⁴CO₂. Increased oxygen enhanced both the rate and extent of degradation. However, whereas Pleurotus ostreatus, Pycnoporus cinnabarinus 115 and Pycnoporus cinnabarinus A-360 degraded 12–17% of ¹⁴C-(U)-lignin of poplar wood to ¹⁴CO₂ also in an air atmosphere, Sporotrichum pulverulentum, Phlebia radiata 79 and Phanerochaete sordida 37 degraded only 1–5% under these conditions. Addition of cellulose and glucose to the poplar wood medium stimulated degradation of ¹⁴C-(RING)-lignin of poplar wood by Phlebia radiata 79 but repressed degradation by Polyporus versicolor and Pleurotus ostreatus. Cellulose added to the wood meal medium had no effect on the degradation of lignin by Phanerochaete sordida 37 and Sporotrichum pulverulentum but glucose slightly repressed lignin degradation by these fungi. Those white-rot fungi which were considered as preferentially lignin attacking fungi could degrade ¹⁴C-(RING)-lignin of poplar wood efficiently under 100% oxygen. They did not require an extra energy source in addition to wood meal polysaccharides for rapid ring cleavage and they degraded up to 50–60% of the ¹⁴C-lignin to ¹⁴CO₂ in 6–7 weeks at a maximum rate of 3–4% per day.These results were reported in part at the Journées Internationales d'Etudes du Groupe Polyphenols, 29. 9.–1. 10. 1982, Université Paul Sabatier, Toulouse, France     

Effect of three strains of Pleurotus tuber-regium (Fr.) Sing. on chemical composition and rumen fermentation of wheat straw

This study was conducted to investigate changes in in vitro dry matter digestibility (IVDMD) and cell wall constituent degradation in wheat straw treated with 3 strains of the fungus Pleurotus tuber-regium (PT). The incubation of wheat straw for 30 days at 28 degrees C improved IVDMD from 30.3% (UWS-untreated wheat straw) to 47.1% for strain PT1, to 48.5% for PT4, and was unchanged IVDMD-29.9% -for PT5. The growth of fungi was accompanied by the dry matter loss of wheat straw: 31.5% for PT1, 20.9% for PT4, and 4.8% for PT5. Fungal treatment was characterized by increased crude protein and ash contents (%) in all fungi-treated straws and reduced hemicellulose and lignin content. It is evident that enzymes of all 3 PT strains preferentially degraded hemicellulose and lignin over cellulose. Wheat straw treated with PT1 (TWS-PT1), PT4 (TWS-PT4), and PT5 (TWS-PT5) and barley (80% : 20%) were used as the experimental diets at the fermentation in the artificial rumen. UWS with barley (80% : 20%) served as the control diet. The fermentation of experimental diets was accompanied with increased IVDMD and a very low degree of hemicellulose degradation. Total gas and methane productions were similar in all diets. Moreover, total volatile fatty acid (VFA) production (mmol day(-1)), mol % of acetate, propionate, butyrate, isobutyrate, and isovalerate were not influenced during the fermentation of experimental diets. From the stoichiometric relations, production, utilization, and recovery of metabolic hydrogen and organic matter fermented were unchanged. Only the recovery of metabolic hydrogen in TWS-PT5 was significantly increased in comparison to control diet. Total microbial production showed the tendency of lower values in experimental diets, and it was accompanied with a significant decrease of ammonia nitrogen (mg L(-1)). Finally the results showed that the strains of Pleurotus tuber-regium can improve the quality of wheat straw, but the loss of dry matter (DM) (mainly hemicellulose) limits the effective utilization of fungi-treated straw in ruminant digestion.     

Enhancing the mineralization of [U-14C]dibenzo-p-dioxin in three different soils by addition of organic substrate or inoculation with white-rot fungi

The potential for aerobic mineralization of [U-¹⁴C]dibenzo-p-dioxin (DD) was investigated in samples of three different agricultural soils already contaminated with polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) by industrial activities. The influence of amendments, i.e. wheat straw and compost, and of soil treatment by inoculation with lignolytic fungi, grown on wheat straw substrate, was tested. All the soils tested contained an indigenous DD-mineralizing microflora. The soil characterized by the highest organic matter content and the highest content of soil microbial biomass displayed the best DD mineralization of 36.6% within 70 days, compared with the two organic-matter-poor soils with an endogenous DD mineralization of 19.5% and 23.3% respectively. Amendments with compost increased DD mineralization up to 28% in both soils with low organic matter and microbial biomass content, but did not affect mineralization in the organic-matter-rich soil. Addition of wheat straw had no constant influence on DD mineralization in the soils tested. The best DD mineralization resulted from inoculation with lignolytic white-rot fungi (Phanerochaete chrysosporium, Pleurotus sp. Florida, Dichomitus squalens) and with an unidentified lignolytic fungus, which was isolated originally from a long-term PCDD/F-contaminated soil. A mineralization of up to 50% within 70 days was reached by this treatment. The influence of inoculated fungi on mineralization differed between the soils investigated. Received: 14 April 1997 / Received revision: 24 June 1997 / Accepted: 29 June 1997     

Lignin solubilisation by Thermomonospora mesophila

Summary Thermomonospora mesophila degraded [¹⁴C]lignin-labelled wheat lignocellulose to yield high molecular weight water-soluble products and a small amount of ¹⁴CO₂. Solubilisation of [¹⁴C]lignin was found to be extracellular and inducible by growth on lignocellulose (straw) and hemicellulose (xylan), but was not correlated with xylanase or cellulase production.The acid-precipitable product of straw degradation by T. mesophila was found to be a complex of lignin, pentose-rich carbohydrate and protein with some similarity to humic acids. Solid-state ¹³C-NMR spectra of the dried product were generally similar to those of chemically extracted milled straw lignin but showed an increased content of carbonyl groups.The relationship between degradation and solubilisation of lignin is discussed and a role suggested for actinomycetes in humification and the exploitation of lignocellulose bioconversion.     

Effect of enzyme extracts isolated from white-rot fungi on chemical composition and in vitro digestibility of wheat straw

A series of in vitro experiments were completed to evaluate the potential of enzyme extracts, obtained from the white-rot fungi Trametes versicolor (TV1, TV2), Bjerkandera adusta (BA) and Fomes fomentarius (FF), to increase degradation of cell wall components of wheat straw. The studies were conducted as a completely randomized design and analysed using one-way ANOVA. Enzyme activities of the extracts, previously obtained from a liquid culture medium, were characterized in terms of laccase and peroxidase for ligninolytic activity. Carboxymethyl cellulase (CMCase) and avicell digesting cellulase (Avicelase) were used for cellulolytic enzyme assays. Wheat straw samples were incubated with enzyme extracts in a citrate buffer (pH 5.0) in a forced air oven at 25 °C for 6 days. In vitro NDF digestibility (IVNDFD), and the rate and extent of NDF fermentation, without and after incubation with the white-rot enzyme extracts, were determined using a gravimetric microbiological method and a gas production technique, respectively. Results from cell wall chemical composition showed that TV2 and BA enzyme extracts decreased NDF concentration (P<0.05) and that TV1 had higher activity (P<0.05) towards cellulose. There was an increase in IVNDFD (P<0.05), resulting from treatment of wheat straw with enzyme extracts from BA, TV1 and TV2, reaching a difference of 13% for TV2 (P<0.05), versus the non-treated straw control. Treatment with enzyme extract from TV2 caused increased gas production (P<0.05) after the first 20 h of incubation, and also increased the maximum rate of gas production, thus enhancing fermentation kinetics. This study indicates that enzyme extracts from white-rot fungi can be used to develop new approaches to overcome low digestibility of some plant cell walls. Utilization of different substrates to produce enzyme extracts can lead to production of viable ligninolytic complexes which could improve the nutritive value of fibrous feeds.     

Metabolism of 2,4,6-trinitrotoluene by the white-rot fungus Bjerkandera adusta DSM 3375 depends on cytochrome P-450

Degradation of 2,4,6-trinitrotoluene (TNT) by the white-rot fungus Bjerkandera adusta DSM 3375 was studied in relation to extracellular ligninolytic activities. The Mn(II)-dependent peroxidase, the only ligninolytic enzyme detectable, reached a maximum activity of 600 ± 159 U/l after incubation in mineral medium with a sufficient nitrogen source. In contrast, the highest extent of [¹⁴C]TNT mineralization was detected in malt extract broth, so that the ability of B. adusta to mineralize TNT did not parallel ligninolytic activity. The microsomal fraction of cells grown in the presence of TNT was found to contain 11 pmol cytochrome P-450/mg protein. In cells grown without TNT, no microsomal cytochrome P-450 could be found. Instead, 14 pmol P-450/mg protein was present in the cytosolic fraction of these cells. Cytochrome P-450 apparently affected the TNT metabolism, as shown by inhibitory studies. Addition of the cytochrome P-450 inhibitor piperonyl butoxide diminished the ¹⁴CO₂ release from 21% to 0.9%, as determined after 23 days of incubation, while 1-aminobenzotriazole and metyrapone decreased the mineralization to 8.6% and 6.3% respectively. Mass-balance analysis of TNT degradation in liquid cultures revealed that, by inhibition of cytochrome P-450, the TNT-derived radioactivity associated with biomass and with polar, water-soluble metabolites decreased from 93.9% to 15.0% and the fraction of radiolabelled metabolites extractable with organic solvents fell to 92.6%. The TNT metabolites of this fraction were identified as aminodinitrotoluenes, indicating that this initial transformation product of TNT may function as a substrate for cytochrome-P-450-dependent reactions in B. adusta. Received: 27 May 1999 / Received revision: 19 August 1999 / Accepted: 19 August 1999     

Evaluation of different lignocellulosic substrates for the production of cellulases and xylanases by the basidiomycete fungi <Emphasis Type="Italic">Bjerkandera adusta</Emphasis> and <Emphasis Type="Italic">Pycnoporus sanguineus</Emphasis>

Agricultural waste products are potential resources for the production of a number of industrial compounds, including biofuels. Basidiomycete fungi display a battery of hydrolytic enzymes with prospective use in lignocellulosic biomass transformation, however little work has been done regarding the characterization of such activities. Growth in several lignocellulosic substrates (oak and cedar sawdust, rice husk, corn stubble, wheat straw and Jatropha seed husk) and the production of cellulases and xylanases by two basidiomycete fungi: Bjerkandera adusta and Pycnoporus sanguineus were analyzed. Growth for P. sanguineus was best in rice husk while corn stubble supported the highest growth rate for B. adusta. Among the substrates tested, cedar sawdust produced the highest cellulolytic activities in both fungal species, followed by oak sawdust and wheat straw. Xylanolytic activity was best in oak and cedar sawdust for both species. We found no correlation between growth and enzyme production. Zymogram analysis of xylanases and cellulases showed that growth in different substrates produced particular combinations of protein bands with hydrolytic activity.     

Biodegradation of chestnut shell and lignin-modifying enzymes production by the white-rot fungi Dichomitus squalens,Phlebia radiata

As a discarded lignocellulosic biomass, chestnut shell is of great potential economic value, thus a sustainable strategy is needed and valuable for utilization of this resource. Herein, the feasibility of biological processes of chestnut shell with Dichomitus squalens, Phlebia radiata and their co-cultivation for lignin-modifying enzymes (LMEs) production and biodegradation of this lignocellulosic biomass was investigated under submerged cultivation. The treatment with D. squalens alone at 12 days gained the highest laccase activity (9.42 ± 0.73 U mg^?1). Combined with the data of laccase and manganese peroxidase, oxalate and H₂O₂ were found to participate in chestnut shell degradation, accompanied by a rapid consumption of reducing sugar. Furthermore, specific surface area of chestnut shell was increased by 77.6–114.1 % with the selected fungi, and total pore volume was improved by 90.2 % with D. squalens. Meanwhile, the surface morphology was observably modified by this fungus. Overall, D. squalens was considered as a suitable fungus for degradation of chestnut shell and laccase production. The presence of LMEs, H₂O₂ and oxalate provided more understanding for decomposition of chestnut shell by the white-rot fungi.     

Biodegradation of azo and phthalocyanine dyes by Trametes versicolor and Bjerkandera adusta

Eighteen fungal strains, known for their ability to degrade lignocellulosic material or lignin derivatives, were screened for their potential to decolorize commercially used reactive textile dyes. Three azo dyes, Reactive Orange 96, Reactive Violet 5 and Reactive Black 5, and two phthalocyanine dyes, Reactive Blue 15 and Reactive Blue 38, were chosen as representatives of commercially used reactive dyes. From the 18 tested fungal strains only Bjerkandera adusta, Trametes versicolor and Phanerochaete chrysosporium were able to decolorize all the dyes tested. During degradation of the nickel-phthalocyanine complex, Reactive Blue 38, by B. adusta and T. versicolor respectively, the toxicity of this dye to Vibrio fischeri was significantly reduced. In the case of Reactive Violet 5, a far-reaching detoxification was achieved by treatment with B. adusta. Reactive Blue 38 and Reactive Violet 5 were decolorized by crude exoenzyme preparations from T. versicolor and B. adusta in a H₂O₂-dependent reaction. Specific activities of the exoenzyme preparations with the dyes were determined and compared to oxidation rates by commercial horseradish peroxidase. Received: 3 February 1997 / Received revision: 9 April 1997 / Accepted: 13 April 1997     

Lignocellulose Decomposition and Production of Ligninolytic Enzymes During Interaction of White Rot Fungi with Soil Microorganisms

Abstract Four strains of white rot fungi, including two strains of Pleurotus sp., one Dichomitus squalens, and one Ganoderma applanatum, were grown on milled straw. After colonization of the straw by the fungi, sterile or nonsterile plugs of soil were added to the fungal substrates. The influence of the sterile soil and the indigenous soil microbiota on fungal growth, overall respiration, and production of ligninolytic exoenzymes was assessed. A method for extraction of laccase from soil samples was developed. Lignocellulose decomposition, and enzyme production of D. squalens were enhanced by the presence of sterile soil. The availability of inorganic compounds such as manganese may be a trigger for this stimulation. Neither growth nor the production of laccase and manganese peroxidase (MnP) of the Pleurotus strains was markedly affected by the soil microbiota. These fungi were highly competitive with the soil microbiota. It was demonstrated for the first time that the exoenzymes of such fungi are active in nonsterile soil. Enzyme activity in the aqueous phase of soil was high as in the aqueous phase of the straw substrate. D. squalens and G. applanatum did not withstand the competition with the soil microbiota, but the mycelia associated with straw were overgrown by soil microorganisms. Correspondingly, the fungi did not penetrate the soil, decomposition of lignocellulose was impeded, and the activities of laccase and MnP decreased dramatically. Received: 2 April 1996; Accepted: 7 June 1996     

The effect of white-rot basidiomycetes on chemical composition andin Vitro digestibility of wheat straw

Five white-rot basidiomycetes were evaluated for their potential to improve ruminal degradation of wheat straw.Polyorus brumalis, Lyophyllum ulmarium III,Trametes gibbosa, Pleurotus ostreatus, and aPleurotus ostreatus mutant were incubated on wheat straw for 30 d at 28°C. Detergent fiber, crude protein andin vitro dry matter digestibility (IVDMD) were determined. The results showed increasing crude protein and ash contents in fungus-treated straw. IVDMD values were increased in straws treated withP. ostreatus, P. ostreatus mutant andT. gibbosa only. Relative to untreated wheat straw the detergent fiber content—neutral detergent fiber (NDF), and acid detergent fiber (ADF) was reduced in fungus-treated straw and out of three fractions—hemicellulose, cellulose and lignin, hemicellulose showed the largest proportionate loss whereas lignin the smallest one in all 5 samples of fungus treated straw.     

Catabolism of the lignin substructure model compound dehydrodivanillin by a lignin-degrading Streptomyces

The lignin-degrading actinomycete Streptomyces viridosporus T7A readily degrades the lignin model compound dehydrodivanillin. Four mutants of this organism (produced by irradiation of spores with ultraviolet light) were shown to have lost the ability to catabolize dehydrodivanillin. These mutant strains retained an undiminished ability to degrade Douglas-fir lignin (¹⁴C-lignin ¹⁴CO₂) as compared to the wild-type strain. None of the strains accumulated detectable quantities of dehydrodivanillin when grown on lignocellulose. Thus it appears that the enzymes involved in dehydrodivanillin catabolism are not a part of the streptomycete's system for degrading polymeric lignin. It is concluded that dehydrodivanillin is probably not a relevant model compound for study of lignin polymer degradation by Streptomyces viridosporus. Since many stable mutants completely lacking DHDV-degrading ability were readily obtained, it is suggested that the relevant catabolic enzymes may be encoded on a plasmid.Abbreviations DHDV dehydrodivanillin