Kerem Z, Bao W, Hammel K E
Institute for Microbial and Biochemical Technology, U.S. Department of Agriculture Forest Products Laboratory, Madison, WI 53705, USA.
Proc Natl Acad Sci U S A. 1998 Sep 1;95(18):10373-7. doi: 10.1073/pnas.95.18.10373.
Fungi that cause brown rot of wood are essential biomass recyclers and also the principal agents of decay in wooden structures, but the extracellular mechanisms by which they degrade lignocellulose remain unknown. To test the hypothesis that brown-rot fungi use extracellular free radical oxidants as biodegradative tools, Gloeophyllum trabeum was examined for its ability to depolymerize an environmentally recalcitrant polyether, poly(ethylene oxide) (PEO), that cannot penetrate cell membranes. Analyses of degraded PEOs by gel permeation chromatography showed that the fungus cleaved PEO rapidly by an endo route. 13C NMR analyses of unlabeled and perdeuterated PEOs recovered from G. trabeum cultures showed that a major route for depolymerization was oxidative C---C bond cleavage, a reaction diagnostic for hydrogen abstraction from a PEO methylene group by a radical oxidant. Fenton reagent (Fe(II)/H2O2) oxidized PEO by the same route in vitro and therefore might account for PEO biodegradation if it is produced by the fungus, but the data do not rule out involvement of less reactive radicals. The reactivity and extrahyphal location of this PEO-degrading system suggest that its natural function is to participate in the brown rot of wood and that it may enable brown-rot fungi to degrade recalcitrant organopollutants.
引起木材褐腐的真菌是重要的生物质循环利用者，也是木结构腐朽的主要因素，但其降解木质纤维素的胞外机制尚不清楚。为了验证褐腐真菌利用胞外自由基氧化剂作为生物降解工具这一假说，对毛革盖菌降解一种难溶于环境且无法穿透细胞膜的聚醚——聚环氧乙烷（PEO）的能力进行了研究。通过凝胶渗透色谱法对降解后的聚环氧乙烷进行分析，结果表明该真菌通过内切途径快速裂解聚环氧乙烷。对从毛革盖菌培养物中回收的未标记和全氘代聚环氧乙烷进行的13C核磁共振分析表明，主要的解聚途径是氧化碳-碳键断裂，这是一种由自由基氧化剂从聚环氧乙烷亚甲基上夺取氢的反应特征。芬顿试剂（Fe(II)/H2O2）在体外通过相同途径氧化聚环氧乙烷，因此如果它由真菌产生，可能是聚环氧乙烷生物降解的原因，但这些数据并未排除活性较低的自由基的参与。这种聚环氧乙烷降解系统的反应活性和菌丝外位置表明，其天然功能是参与木材的褐腐过程，并且可能使褐腐真菌能够降解难降解的有机污染物。
