真菌发酵胞外多糖的研究进展

真菌胞外多糖具有高黏性、抗氧化、抗病毒和抗肿瘤等多种生物学活性,在食品和医药工业等领域应用广泛。本文结合国内外最新研究成果,综述了近年来有关产胞外多糖的真菌、影响真菌胞外多糖产量的因素、产胞外多糖的菌株的选育策略以及真菌胞外多糖的功能研究,以期为真菌发酵胞外多糖的研究和应用提供参考。     

Atrovenetin as a potent antioxidant compound from penicillium species

We have established a program to screen large numbers of wild-type fungi isolated from soil for potential producers of antioxidants and synergists for tocopherol (Toe). An antioxidant and potent Toc synergist was isolated from mycelial mats ofPenicillium paraherquei. It was one of the deoxyherqueinone-type phenalenones and has been identified as atrovenetin. Under autoxidation conditions, the induction periods of this compound (0.025%) tested by the active oxygen method were 571 and 171 hr in lard with and without Toc (0.04%), respectively. It was also capable of stabilizing vegetable oils such as soybean, rapeseed and palm oils.     

Efrapeptin production byTolypocladium fungi (Deuteromycotina: Hyphomycetes): Intra- and interspecific variation

Production of the mitochondrial ATPase inhibitory peptides efrapeptins was evaluated by HPLC analysis in 44 strains of nine species of the fungal genusTolypocladium (Deuteromycotina: Hyphomycetes). Efrapeptin identification was confirmed by mass spectral data for the first time in the speciesT. cylindrosporum. HPLC retention time data indicated thatT. nubicola andT. tundrense, two species not previously known to produce efrapeptins, also produce the peptides. No efrapeptins were detected (<0.3 mg/100 ml broth) in single strains each ofT. balanoides, T. extinguens, T. parasiticum, andT. microsporum. Five strains ofT. geodes produced detectable amounts of efrapeptins and had compound F, or F and G, as the major component(s) in the mixture with the order of abundance being F> or ∼G > H ∼ D ∼ E > C. Eleven strains ofT. niveum produced detectable amounts of efrapeptins and had efrapeptins D and E as the primary and secondary components, respectively, in the mixture with the order of abundance being D > E > F > C ∼ G. A singleT. niveum strain had an efrapeptin profile similar to that of theT. geodes strains. Ten strains ofT. cylindrosporum had detectable amounts of efrapeptins. Of these, nine had F and one had G as the major component.T. cylindrosporum had higher ratios of E to D than didT. geodes. Efrapeptins were detected in one of twoT. nubicola strains analyzed (F > G > H) and one of threeT. tundrense strains (F > G > H > E).T. niveum strains could, in most cases, be identified to species on the basis of their efrapeptin profiles. Mention of a commercial or proprietary product does not constitute an endorsement by the USDA.     

Conserved Opposite Functions in Plant Resistance to Biotrophic and Necrotrophic Pathogens of the Immune Regulator SRFR1

Plant immunity is mediated in large part by specific interactions between a host resistance protein and a pathogen effector protein, named effector-triggered immunity (ETI). ETI needs to be tightly controlled both positively and negatively to enable normal plant growth because constitutively activated defense responses are detrimental to the host. In previous work, we reported that mutations in SUPPRESSOR OF rps4-RLD1 (SRFR1), identified in a suppressor screen, reactivated EDS1-dependent ETI to Pseudomonas syringae pv. tomato (Pto) DC3000. Besides, mutations in SRFR1 boosted defense responses to the generalist chewing insect Spodoptera exigua and the sugar beet cyst nematode Heterodera schachtii. Here, we show that mutations in SRFR1 enhance susceptibility to the fungal necrotrophs Fusarium oxysporum f. sp. lycopersici (FOL) and Botrytis cinerea in Arabidopsis. To translate knowledge obtained in AtSRFR1 research to crops, we generated SlSRFR1 alleles in tomato using a CRISPR/Cas9 system. Interestingly, slsrfr1 mutants increased expression of SA-pathway defense genes and enhanced resistance to Pto DC3000. In contrast, slsrfr1 mutants elevated susceptibility to FOL. Together, these data suggest that SRFR1 is functionally conserved in both Arabidopsis and tomato and functions antagonistically as a negative regulator to (hemi-) biotrophic pathogens and a positive regulator to necrotrophic pathogens.     

Development of a Highly Sensitive β-Glucan Detection System Using Scanning Single-Molecule Counting Method

To overcome the limitations of the Limulus amebocyte lysate (LAL) assay method for the diagnosis of invasive fungal infection, we applied a reaction system combining recombinant β-glucan binding proteins and a scanning single-molecule counting (SSMC) method. A novel (1→3)-β-D-glucan recognition protein (S-BGRP) and a (1→6)-β-glucanase mutant protein were prepared and tested for the binding of (1→6)-branched (1→3)-β-D-glucan from fungi. S-BGRP and (1→6)-β-glucanase mutant proteins reacted with β-glucan from Candida and Aspergillus spp. Although LAL cross-reacted with plant-derived β-glucans, the new detection system using the SSMC method showed low sensitivity to plant (1→3)-β-D-glucan, which significantly improved the appearance of false positives, a recognized problem with the LAL method. Measurement of β-glucan levels by the SSMC method using recombinant β-glucan-binding proteins may be useful for the diagnosis of fungal infections. This study shows that this detection system could be a new alternative diagnostic method to the LAL method.     

Volatiles of Bracket Fungi Fomitopsis pinicola and Fomes fomentarius and Their Functions as Insect Attractants

Volatiles released from fruiting bodies of the polypores Fomitopsis pinicola and Fomes fomentarius (Polyporaceae) were collected by entrainment and SPME techniques and analyzed by GC-MS. The most significant difference between the two species was found in the terpene fraction. F. fomentarius emitted a more complex blend, with more than 10 sesquiterpenes. During the sporulating phase, the release of (R)- and (S)-oct-1-en-3-ol, octan-3-one, and some sesquiterpene hydrocarbons (mainly -barbatene) increased in F. pinicola, whereas in F. fomentarius the release of octan-3-one, cis-furanoid linalool oxide, -phellandrene, -myrcene, and several sesquiterpene hydrocarbons increased. -Barbatene was identified for the first time in fungi. Chopping of the fruiting bodies altered the odor composition more in F. fomentarius than in F. pinicola. Five volatiles giving a typical fungal odor (rac-oct-1-en-3-ol, nonan-1-ol, rac-octan-3-ol, octan-1-ol, and octan-3-one) were tested for insect attraction in the field. Females of the three wood-living generalist beetles Malthodes fuscus, Anaspis marginicollis, and A. rufilabris and both sexes of the moth Epinotia tedella were attracted to rac-oct-1-en-3-ol. The generalist predator on fungus-insects Lordithon lunulatus was attracted to rac-oct-1-en-3-ol and octan-3-one in combination. Previous results regarding the host-specific attraction of beetles to the odors emanating from chopped fruiting bodies of F. pinicola and F. fomentarius are discussed in the light of this investigation.