Presley Gerald N, Schilling Jonathan S
University of Minnesota Department of Bioproducts and Biosystems Engineering, St. Paul, Minnesota, USA.
University of Minnesota Department of Bioproducts and Biosystems Engineering, St. Paul, Minnesota, USA
Appl Environ Microbiol. 2017 Mar 17;83(7). doi: 10.1128/AEM.02987-16. Print 2017 Apr 1.
Brown rot fungi are wood-degrading fungi that employ both oxidative and hydrolytic mechanisms to degrade wood. Hydroxyl radicals that facilitate the oxidative component are powerful nonselective oxidants and are incompatible with hydrolytic enzymes unless they are spatially segregated in wood. Differential gene expression has been implicated in the segregation of these reactions in , but it is unclear if this two-step mechanism varies in other brown rot fungi with different traits and life history strategies that occupy different niches in nature. We employed proteomics to analyze a progression of wood decay on thin wafers, using brown rot fungi with significant taxonomic and niche distances: (Boletales; "dry rot" lumber decay) and (order Gloeophyllales; slash, downed wood). Both fungi produced greater oxidoreductase diversity upon wood colonization and greater glycoside hydrolase activity later, consistent with a two-step mechanism. The two fungi invested very differently, however, in terms of growth (infrastructure) versus protein secretion (resource capture), with the ergosterol/extracted protein ratio being 7-fold higher with than with In line with the native substrate associations of these fungi, hemicellulase-specific activities were dominated by mannanase in and by xylanase in Consistent with previous observations, did not produce glycoside hydrolase 6 (GH6) cellobiohydrolases (CBHs) in this study, despite taxonomically belonging to the order Boletales, which is distinguished among brown rot fungi by having CBH genes. This work suggests that distantly related brown rot fungi employ staggered mechanisms to degrade wood, but the underlying strategies vary among taxa. Wood-degrading fungi are important in forest nutrient cycling and offer promise in biotechnological applications. Brown rot fungi are unique among these fungi in that they use a nonenzymatic oxidative pretreatment before enzymatic carbohydrate hydrolysis, enabling selective removal of carbohydrates from lignin. This capacity has independently evolved multiple times, but it is unclear if different mechanisms underpin similar outcomes. Here, we grew fungi directionally on wood wafers and we found similar two-step mechanisms in taxonomically divergent brown rot fungi. The results, however, revealed strikingly different growth strategies, with investing more in biomass production than secretion of proteins and showing the opposite pattern, with a high diversity of uncharacterized proteins. The "simplified" secretomic system could help narrow gene targets central to oxidative brown rot pretreatments, and a comparison of its distinctions with and other brown rot fungi (e.g., ) might offer similar traction in noncatabolic genes.
褐腐真菌是利用氧化和水解机制来降解木材的木材降解真菌。促进氧化成分的羟基自由基是强大的非选择性氧化剂，除非它们在木材中空间隔离，否则与水解酶不相容。差异基因表达与这些反应在……中的隔离有关，但尚不清楚这种两步机制在自然界中占据不同生态位、具有不同特征和生活史策略的其他褐腐真菌中是否有所不同。我们采用蛋白质组学方法分析了薄木片上木材腐朽的进程，使用了具有显著分类学和生态位差异的褐腐真菌：……（牛肝菌目；“干腐”木材腐朽）和……（革盖菌目；砍伐后的木材、倒木）。两种真菌在木材定殖时都产生了更多样的氧化还原酶，随后糖苷水解酶活性增强，这与两步机制一致。然而，这两种真菌在生长（基础设施）与蛋白质分泌（资源捕获）方面的投入差异很大，……的麦角固醇/提取蛋白比率比……高7倍。与这些真菌的天然底物关联一致，……的半纤维素酶特异性活性以甘露聚糖酶为主，而……以木聚糖酶为主。与之前的观察结果一致，在本研究中，……尽管在分类学上属于牛肝菌目，而牛肝菌目在褐腐真菌中因具有纤维二糖水解酶（CBH）基因而有别于其他类群，但它并未产生糖苷水解酶6（GH6）纤维二糖水解酶（CBH）。这项工作表明，亲缘关系较远的褐腐真菌采用交错机制来降解木材，但不同类群的潜在策略有所不同。木材降解真菌在森林养分循环中很重要，并且在生物技术应用中具有前景。褐腐真菌在这些真菌中独一无二，因为它们在酶促碳水化合物水解之前使用非酶促氧化预处理，从而能够从木质素中选择性去除碳水化合物。这种能力已经独立进化了多次，但尚不清楚不同的机制是否支撑了相似的结果。在这里，我们让真菌在木片上定向生长，并且我们在分类学上不同的褐腐真菌中发现了相似的两步机制。然而，结果显示出截然不同的生长策略，……在生物量生产上的投入比蛋白质分泌更多，而……则呈现相反的模式，具有高度多样的未表征蛋白质。“简化”的……分泌组系统可能有助于缩小氧化褐腐预处理核心的基因靶点，并且将其与……和其他褐腐真菌（例如……）的差异进行比较，可能会在非分解代谢基因方面提供类似的线索。
