Degradation of cellulose by basidiomycetous fungi

Cellulose is the main polymeric component of the plant cell wall, the most abundant polysaccharide on Earth, and an important renewable resource. Basidiomycetous fungi belong to its most potent degraders because many species grow on dead wood or litter, in environment rich in cellulose. Fungal cellulolytic systems differ from the complex cellulolytic systems of bacteria. For the degradation of cellulose, basidiomycetes utilize a set of hydrolytic enzymes typically composed of endoglucanase, cellobiohydrolase and beta-glucosidase. In some species, the absence of cellobiohydrolase is substituted by the production of processive endoglucanases combining the properties of both of these enzymes. In addition, systems producing hydroxyl radicals based on cellobiose dehydrogenase, quinone redox cycling or glycopeptide-based Fenton reaction are involved in the degradation of several plant cell wall components, including cellulose. The complete cellulolytic complex used by a single fungal species is typically composed of more than one of the above mechanisms that contribute to the utilization of cellulose as a source of carbon or energy or degrade it to ensure fast substrate colonization. The efficiency and regulation of cellulose degradation differs among wood-rotting, litter-decomposing, mycorrhizal or plant pathogenic fungi and yeasts due to the different roles of cellulose degradation in the physiology and ecology of the individual groups.     

Nylon biodegradation by lignin-degrading fungi.

The biodegradation of nylon by lignin-degrading fungi was investigated. The fungus IZU-154 significantly degraded nylon-66 membrane under ligninolytic conditions. Nuclear magnetic resonance analysis showed that four end groups, CHO, NHCHO, CH3, and CONH2, were formed in the biodegraded nylon-66 membranes, suggesting that nylon-66 was degraded oxidatively.     

Sorption of heavy metals by four basidiomycetous fungi

Biosorptions of Pb²⁺, Cr⁶⁺, Cd²⁺ and Ni²⁺ were investigated, with special emphasis on the first one, using live and dead fungal mycelia. Of the four fungi, namely Polyporus ostreiformis, Volvariella volvacea, Pleurotus sajor-caju and Phanerochaete chrysosporium, the last one was found to be most effective in Pb²⁺ removal. Total biosorption was effected in 6 days up to the Pb²⁺ concentration of 6 mg/l, with a specific uptake of 1.33 mg Pb²⁺/g dry cell mass. The removal of other three metals varied between 28.8–73.3% from a medium containing 4 mg/l of each of the metals.Laboratory facilities created under M.Tech programme in Biotechnology and Engineering (sponsored by Department of Biotechnology, Govt. of India) were partly utilized for this study.     

Removal and mineralization of polycyclic aromatic hydrocarbons by litter-decomposing basidiomycetous fungi

Nine strains of litter-decomposing fungi, representing eight species of agaric basidiomycetes, were tested for their ability to remove a mixture of three polycyclic aromatic hydrocarbons (PAHs) (total 60 mg l(-1)) comprising anthracene, pyrene and benzo(a)pyrene (BaP) in liquid culture. All strains were able to convert this mixture to some extent, but considerable differences in degradative activity were observed depending on the species, the Mn(II) concentration, and the particular PAH. Stropharia rugosoannulata was the most efficient degrader, removing or transforming BaP almost completely and about 95% of anthracene and 85% of pyrene, in cultures supplemented with 200 micro M Mn(II), within 6 weeks. In contrast less than 40, 18, and 50% BaP, anthracene and pyrene, respectively, were degraded in the absence of supplemental Mn(II). In the case of Stropharia coronilla, the presence of Mn(II) led to a 20-fold increase of anthracene conversion. The effect of manganese could be attributed to the stimulation of manganese peroxidase (MnP). The maximum activity of MnP increased in S. rugosoannulata cultures from 10 U l(-1) in the absence of Mn(II) to 320 U l(-1) in Mn(II)-supplemented cultures. The latter degraded about 6% of a (14)C-labeled BaP into (14)CO(2) whereas only 0.7% was mineralized in the absence of Mn(II). In solid-state straw cultures, S. rugosoannulata, S. coronilla and Agrocybe praecox mineralized between 4 and 6% of (14)C-labeled BaP within 12 weeks.     

Catabolism of benzene compounds by ascomycetous and basidiomycetous yeasts and yeastlike fungi

A literature review is given on growth of yeasts on benzene compounds and on the catabolic pathways involved. Additionally, a yeast collection was screened for assimilation of phenol and 3-hydroxybenzoic acid. Fifteen ascomycetous and thirteen basidiomycetous yeast species were selected and were tested for growth on 84 benzene compounds. It appeared that 63 of these compounds supported growth of one or more yeast species. The black yeastExophiala jeanselmei assimilated 54 of these compounds.The catechol branch of the 3-oxoadipate pathway and its hydroxyhydroquinone variant were involved in phenol and resorcinol catabolism of ascomycetes as well as of basidiomycetes. However, these two groups of yeasts showed characteristic differences in hydroxybenzoate catabolism. In the yeastlike fungusE. jeanselmei and in basidiomycetes of the generaCryptococcus, Leucosporidium andRhodotorula, the protocatechuate branch of the 3-oxoadipate pathway was induced by growth on 3- and 4-hydroxybenzoic acids. In threeTrichosporon species and in all ascomycetous yeasts tested, 4-hydroxybenzoic acid was catabolyzed via protocatechuate and hydroxyhydroquinone. These yeasts were unable to cleave protocatechuate. 3-Hydroxybenzoic and 3-hydroxycinnamic acids were catabolized in ascomycetous yeasts via the gentisate pathway, but in basidiomycetes via protocatechuate.Incomplete oxidation of phenol, some chlorophenols, cresols and xylenols was observed in cultures ofCandida parapsilosis growing on hydroquinone. Most compounds transformed by the growing culture were also converted by the phenol monooxygenase present in cell-free extracts of this yeast. They did not support growth.The relationship between the ability of ascomycetous yeasts to assimilate n-alkanes, amines and benzene compounds, and the presence of Coenzyme Q₉ is discussed.     

Ubiquity of lignin-degrading peroxidases among various wood-degrading fungi.

Phanerochaete chrysosporium is rapidly becoming a model system for the study of lignin biodegradation. Numerous studies on the physiology, biochemistry, chemistry, and genetics of this system have been performed. However, P. chrysosporium is not the only fungus to have a lignin-degrading enzyme system. Many other ligninolytic species of fungi, as well as other distantly related organisms which are known to produce lignin peroxidases, are described in this paper. In this study, we demonstrated the presence of the peroxidative enzymes in nine species not previously investigated. The fungi studied produced significant manganese peroxidase activity when they were grown on an oak sawdust substrate supplemented with wheat bran, millet, and sucrose. Many of the fungi also exhibited laccase and/or glyoxal oxidase activity. Inhibitors present in the medium prevented measurement of lignin peroxidase activity. However, Western blots (immunoblots) revealed that several of the fungi produced lignin peroxidase proteins. We concluded from this work that lignin-degrading peroxidases are present in nearly all ligninolytic fungi, but may be expressed differentially in different species. Substantial variability exists in the levels and types of ligninolytic enzymes produced by different white not fungi.     

Degradation of xenobiotic compounds by lignin-degrading white-rot fungi: enzymology and mechanisms involved

White-rot fungi (WRF) are ubiquitous in nature with their natural ability to compete and survive. WRF are the only organisms known to have the ability to degrade and mineralize recalcitrant plant polymer lignin. Their potential to degrade second most abundant carbon reserve material lignin on the earth make them important link in global carbon cycle. WRF degrade lignin by its unique ligninolytic enzymatic machinery including lignin peroxidase, manganese peroxidase, laccase, cellobiose dehydrogenase, H2O2-generating enzymes, etc. The ligninolytic enzymes system is non-specific, extracellular and free radical based that allows them to degrade structurally diverse range of xenobiotic compounds. Lignin peroxidase and manganese peroxidase carry out direct and indirect oxidation as well as reduction of xenobiotic compounds. Indirect reactions involved redox mediators such as veratryl alcohol and Mn2+. Reduction reactions are carried out by carboxyl, superoxide and semiquinone radicals, etc. Methylation is used as detoxification mechanism by WRF. Highly oxidized chemicals are reduced by transmembrane redox potential. Degradation of a number of environmental pollutants by ligninolytic system of white rot fungi is described in the present review.     

Use of lignin-degrading fungi in the disposal of pentachlorophenol-treated wood

Summary The lignin-degrading fungiPhanerochaete chrysosporium, P. sordida, Trametes hirsuta, andCeriporiopsis subvermispora were evaluated for their ability to decrease the concentration of pentachlorophenol (PCP) and to cause dry weight loss in PCP-treated wood. Hardwood and softwood materials from PCP-treated ammunition boxes that were chipped to pass a 3.8-cm screen were used. All four fungi caused significant weight losses and decreases in the PCP concentration. The largest PCP decrease (84% in 4 weeks) was caused byT. hirsuta, and the smallest decrease was caused byC. subvermispora (37% in 4 weeks). After 4 weeks, the fate of spiked¹⁴C[PCP] in softwood chips inoculated withT. hirsuta was as follows: 27% was mineralized, 42.5% was non-extractable and bound to the chips, 23.5% was associated with fungal hyphae, and 6% was organic-extractable. Decreases of PCP byP. chrysosporium andP. sordida averaged 59% and 57%, respectively. PCP decreases caused byPhanerochaete spp. were not significantly affected by wood type or sterilization and were primarily due to methylation of PCP that resulted in accumulation of pentachloroanisole. Softwood weight losses caused byT. hirsuta, P. chrysosporium andC. subvermispora were respectively, 24, 6.5, and 17%, after 4 weeks. These weight losses are comparable to reported weight losses by these organisms in non-treated softwood. Nutrient supplementation significantly increased weight loss but not percentage decrease of PCP. The results of this research demonstrate the potential for using lignin-degrading fungi to destroy PCP-treated wood.     

Comparison of two lignin-degrading fungi:Phlebia radiata andPhanerochaete chrysosporium

Summary The ligninolytic enzymes ofPhlebia radiata were produced in static conditions earlier developed forPhanerochaete chrysosporium. The production pattern of lignin peroxidases resembled that ofP. chrysosporium. The extracellular proteins ofPhlebia radiata were separated by isoelectric focusing. Four proteins with acidic isoelectric points (4.15) were detected by peroxidase staining. The peroxidases ofP. radiata reacted with antibodies produced against a peroxidase ofPhanerochaete chrysosporium and vice versa. Thus the lignin peroxidases of the two fungi have major similarities despite slight differences in their isoelectric points and molecular weights. Veratryl alcohol was produced by both fungi and degraded to veratraldehyde, two lactones and a quinone by the ligninolytic cultures.     

Activities of chitinolytic enzymes during primary and secondary colonization of wood by basidiomycetous fungi

The nitrogen (N) content of wood is usually suboptimal for fungal colonization. During decomposition of wood, an increasing fraction of the N becomes incorporated into fungal mycelium. Between 5 and 50% of the N in wood-degrading mycelium may be incorporated into chitin. Chitinolytic enzymes render this N available for re-utilization. Here, the activities of chitinolytic enzymes produced by wood-rotting fungi during degradation of spruce (Picea abies) wood were quantified in situ using fluorogenic 4-methylumbelliferyl substrates. A new method was developed that enables spatial quantification of enzyme activities on solid surfaces. All of the three tested fungi produced endochitinases, chitobiosidases and N-acetylhexosaminidases during colonization of wood. N-acetylhexosaminidase activity, and in some cases also chitobiosidase and endochitinase activities, were higher during secondary overgrowth of another fungus than during primary colonization of noncolonized wood. The results suggest that wood-degrading fungi degrade their own cell walls as well as the hyphae of earlier colonizers. Recycling of cell wall material within single mycelia and between fungal individuals during succession may lead to retention of N within woody debris.     

食用菌生物修复重金属污染研究进展

生物修复是利用生物体及其衍生物对重金属进行吸收/吸附来处理环境中重金属污染的方法,具有成本低、来源广、无二次污染等特点.食用菌富集重金属是生物修复的一个重要研究方向,食用菌修复作用主要通过对重金属的吸收来降低其生态毒性,从而对重金属污染起到一定的修复作用.本文论述了食用菌对重金属Cu、Cd、Pb、Zn、As、Cr的富集作用,揭示了食用菌富集重金属的可能机理,并对采用食用菌富集重金属以治理环境污染的前景进行了展望.     

Dye decolorization by sub-tropical basidiomycetous fungi and the effect of metals on decolorizing ability

White-rot basidiomycetous fungi from sub-tropical forests plus a Phanerochaete chrysosporium control were able to decolorize several azo, triphenylmethane and heterocyclic/polymeric dyes over 14 days. The effects of metal ions on decolorizing ability towards the dye Poly-R varied. Two sub-tropical strains were capable of decolorization in the presence of up to 0.25 mM Cd²⁺, Cu²⁺ and Zn²⁺, whereas decolorization by P. chrysosporium was completely inhibited by all metals at concentrations as low as 0.1 mM. In all cases decolorizing ability was more sensitive than biomass production to metal inhibition.     

Bioremediation of DDT contaminated soil using brown-rot fungi

The ability of brown-rot fungi (BRF) to eliminate DDT in artificially and historically contaminated soil was investigated to determine whether the BRF would be suitable for the bioremediation of DDT in soil. Gloeophyllum trabeum, Fomitopsis pinicola and Daedalea dickinsii showed an ability to eliminate DDT in artificially contaminated sterilized (SL) and un-sterilized (USL) soils. The addition of Fe²⁺ to the soil system enhanced the ability of some BRF to eliminate DDT. In the contaminated SL soil, the DDT was eliminated by approximately 41%, 9% and 15% by G. trabeum, F. pinicola and D. dickinsii, respectively. Compared with the controls, in the USL soil approximately 43%, 29% and 32% of DDT was eliminated and approximately 20%, 9% and 26% of DDD (1,1-dichloro-2,2-bis (4-chlorophenyl) ethane) was detected as a metabolic product with G. trabeum, F. pinicola and D. dickinsii, respectively. Of the BRF, G. trabeum demonstrated the greatest ability to eliminate DDT both in the SL and USL soils. G. trabeum was applied to a historically contaminated soil which had a DDT concentration more than three times the artificially contaminated soil. G. trabeum remediated about 64% of the initial DDT with the addition of Fe²⁺. There were no significant differences in the results with or without the addition of Fe²⁺, indicating that G. trabeum can be used directly for the degradation of DDT in soil without any other additional treatment. This study identified that G. trabeum is the most promising BRF for use in the bioremediation of DDT contaminated soil.     

Biodegradation of tetrabromobisphenol A by oxidases in basidiomycetous fungi and estrogenic activity of the biotransformation products

Tetrabromobisphenol A (TBBPA) degradation was investigated using white rot fungi and their oxidative enzymes. Strains of the Trametes, Pleurotus, Bjerkandera and Dichomitus genera eliminated almost 1 mM TBBPA within 4 days. Laccase, whose role in TBBPA degradation was demonstrated in fungal cultures, was applied to TBBPA degradation alone and in combination with cellobiose dehydrogenase from Sclerotium rolfsii. Purified laccase from Trametes versicolor degraded approximately 2 mM TBBPA within 5 h, while the addition of cellobiose dehydrogenase increased the degradation rate to almost 2.5 mM within 3 h. Laccase was used to prepare TBBPA metabolites 2,6-dibromo-4-(2-hydroxypropane-2-yl) phenol (1), 2,6-dibromo-4-(2-methoxypropane-2-yl) phenol (2) and 1-(3,5-dibromo-4-hydroxyphen-1-yl)-2,2',6,6'-tetrabromo-4,4'-isopropylidene diphenol (3). As compounds 1 and 3 were identical to the TBBPA metabolites prepared by using rat and human liver fractions (Zalko et al., 2006), laccase can provide a simple means of preparing these metabolites for toxicity studies. Products 1 and 2 exhibited estrogenic effects, unlike TBBPA, but lower cell toxicity.     

拮抗植物病原真菌的纤维素/木质素降解菌株的筛选及鉴定

【背景】秸秆还田在改善土壤肥力和丰富营养等方面有重要作用,但是也存在秸秆难以快速降解利用和病原真菌病害威胁的问题。【目的】为解决还田秸秆的降解和病原真菌病害问题,从长期秸秆还田地区采集样品,从中筛选出具有降解秸秆和抑菌功能的菌株。【方法】采用稀释分离法、苯胺蓝染色法和刚果红染色法等对秸秆高效降解菌株进行筛选,通过16S rRNA基因测序及构建系统发育树进行菌株鉴定。采用对峙培养法测定筛选到的秸秆降解菌株对玉米大斑病菌(Setostphaeria turcica)、梨黑斑病菌(Alternaria kikuchiana)、马铃薯早疫病菌(Alternaria solani)、链格孢属真菌(Alternaria alternata) ACCC38230和ACCC38231等5种供试植物病原真菌的抑制作用。以玉米大斑病菌(Setostphaeria turcica)为后期供试植物病原真菌,测定拮抗菌株代谢产物的抑菌能力;通过观察拮抗菌株粗提液对玉米大斑病菌分生孢子萌发和菌丝生长的影响,从而测定菌株对病原真菌的抑制作用。【结果】从秸秆还田土壤中分离筛选获得3株高效降解纤维素及木质素菌株并命名为JY122、ZY133和JY215。通过形态学观察和16S rRNA基因测序鉴定上述菌株全部为芽孢杆菌属(Bacillus)。通过系统发育树分析结果表明,JY122与蜡样芽孢杆菌(Bacillus cereus)相似性为99.4%,ZY133与枯草芽孢杆菌(Bacillus subtilis)相似性为100%,JY215与贝莱斯芽孢杆菌(Bacillus velezensis)相似性为99.1%。平板对峙实验结果显示,JY122、ZY133和JY215菌株对不同种属的植物病原真菌均有较强的抑制作用,抑制率高达43.74%-67.54%。此外,上述芽孢杆菌代谢产物具有抑菌活性及很强的热稳定性,经95℃处理后依然具有良好的抑菌效果。【结论】筛选获得的JY122、JY133和JY215菌株具有高效降解纤维素/木质素能力,抑制多种植物病原真菌生长,代谢产物抑菌能力强且热稳定性高。这为玉米秸秆还田提供菌株资源,也为进一步解决秸秆还田难点提供了新方法和思路。     

Universal and species-specific bacterial 'fungiphiles' in the mycospheres of different basidiomycetous fungi

In previous work, several bacterial groups that show a response to fruiting bodies (the mycosphere) of the ectomycorrhizal fungus Laccaria proxima were identified. We here extend this work to a broader range of fungal fruiting bodies sampled at two occasions. PCR-DGGE analyses showed clear effects of the mycosphere of diverse fungi on the total bacterial and Pseudomonas communities in comparison with those in the corresponding bulk soil. The diversities of the Pseudomonas communities increased dramatically in most of the mycospheres tested, which contrasted with a decrease of the diversity of the total bacterial communities in these habitats. The data also indicated the existence of universal (i.e. Pseudomonas poae , P. lini , P. umsongensis , P. corrugata , P. antarctica and Rahnella aquatilis ) as well as specific (i.e. P. viridiflava and candidatus Xiphinematobacter americani) fungiphiles, defined as bacteria adapted to the mycospheres of, respectively, three or more or just one fungal species. The selection of such fungiphiles was shown to be strongly related to their capacities to use particular carbonaceous compounds, as evidenced using principal components analyses of BIOLOG-based substrate utilization tests. The differentiating compounds, i.e. l -arabinose, l -leucine, m-inositol, m-arabitol, d -mannitol and d -trehalose, were tentatively linked to compounds known to occur in mycosphere exudates.     

Bioremediation of crude oil by white rot fungi Polyporus sp. S133

The bioremediation potential of crude oil by Polyporus sp. S133 pre-grown in wood meal was investigated in two separate experiment trials; liquid medium and soil. The effect of three nutrients (glucose, polypeptone, and wood meal), oxygen flow, and some absorbent on the efficiency of the process was also evaluated. Degradation of crude oil in soil was significantly increased with an addition of oxygen flow and some absorbent (kapok and pulp). The highest degradation rate of crude oil was 93% in the soil with an addition of 10% kapok. The present study clearly demonstrates that, if suitably developed, Polyporus sp. S133 could be used to remediate soil contaminated with crude oil.     

Mineralisation of 14C-labelled synthetic lignin and ligninolytic enzyme activities of litter-decomposing basidiomycetous fungi

Within a screening program, 27 soil litter-decomposing basidiomycetes were tested for ligninolytic enzyme activities using agar-media containing 2,2′-azinobis(3-ethylbenzthiazoline-6-sulphonate), a humic acid or Mn²⁺ ions as indicator substrates. Most active species were found within the family Strophariaceae (Agrocybe praecox, Stropharia coronilla, S. rugosoannulata) and used for mineralisation experiments with a ¹⁴C-ring-labelled synthetic lignin (¹⁴C-DHP). The fungi mineralised around 25% of the lignin to ¹⁴CO₂ within 12 weeks of incubation in a straw environment; about 20% of the lignin was converted to water-soluble fragments. Mn-peroxidase was found to be the predominant ligninolytic enzyme of all three fungi in liquid culture and its production was strongly enhanced in the presence of Mn²⁺ ions. The results of this study demonstrate that certain ubiquitous litter-decomposing basidiomycetes possess ligninolytic activities similar to the wood-decaying white-rot fungi, the most efficient lignin degraders in nature. Received: 20 April 2000 / Received revision: 12 July 2000 / Accepted: 16 July 2000