Taillefer Marcel, Arntzen Magnus Ø, Henrissat Bernard, Pope Phillip B, Larsbrink Johan
Wallenberg Wood Science Center, Department of Biology and Biotechnology, Chalmers University of Technology, Gothenburg, Sweden.
Faculty of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, Ås, Norway.
mSystems. 2018 Nov 20;3(6). doi: 10.1128/mSystems.00240-18. eCollection 2018 Nov-Dec.
Bacteria of the phylum are regarded as highly efficient carbohydrate metabolizers, but most species are limited to (semi)soluble glycans. The soil species Cytophaga hutchinsonii and Sporocytophaga myxococcoides have long been known as efficient cellulose metabolizers, but neither species conforms to known cellulolytic mechanisms. Both species require contact with their substrate but do not encode cellulosomal systems of cell surface-attached enzyme complexes or the polysaccharide utilization loci found in many other species. Here, we have fractionated the cellular compartments of each species from cultures growing on crystalline cellulose and pectin, respectively, and analyzed them using label-free quantitative proteomics as well as enzymatic activity assays. The combined results enabled us to highlight enzymes likely to be important for cellulose conversion and to infer their cellular localization. The combined proteomes represent a wide array of putative cellulolytic enzymes and indicate specific and yet highly redundant mechanisms for cellulose degradation. Of the putative endoglucanases, especially enzymes of hitherto-unstudied glycoside hydrolase family, 8 were abundant, indicating an overlooked important role during cellulose metabolism. Furthermore, both species generated a large number of abundant hypothetical proteins during cellulose conversion, providing a treasure trove of targets for future enzymology studies. Cellulose is the most abundant renewable polymer on earth, but its recalcitrance limits highly efficient conversion methods for energy-related and material applications. Though microbial cellulose conversion has been studied for decades, recent advances showcased that large knowledge gaps still exist. Bacteria of the phylum are regarded as highly efficient carbohydrate metabolizers, but most species are limited to (semi)soluble glycans. A few species, including the soil bacteria C. hutchinsonii and S. myxococcoides, are regarded as cellulose specialists, but their cellulolytic mechanisms are not understood, as they do not conform to the current models for enzymatic cellulose turnover. By unraveling the proteome setups of these two bacteria during growth on both crystalline cellulose and pectin, we have taken a significant step forward in understanding their idiosyncratic mode of cellulose conversion. This report provides a plethora of new enzyme targets for improved biomass conversion.
该门细菌被认为是高效的碳水化合物代谢者，但大多数物种仅限于（半）可溶性聚糖。土壤中的哈氏噬纤维菌属物种哈钦森噬纤维菌（Cytophaga hutchinsonii）和粘球菌属物种粘液孢囊粘球菌（Sporocytophaga myxococcoides）长期以来一直被认为是高效的纤维素代谢者，但这两个物种都不符合已知的纤维素分解机制。这两个物种都需要与底物接触，但不编码细胞表面附着的酶复合物的纤维素体系统或许多其他该门物种中发现的多糖利用位点。在这里，我们分别从在结晶纤维素和果胶上生长的培养物中分离出每个物种的细胞区室，并使用无标记定量蛋白质组学以及酶活性测定对它们进行分析。综合结果使我们能够突出可能对纤维素转化很重要的酶，并推断它们的细胞定位。综合蛋白质组代表了大量假定的纤维素分解酶，并表明了纤维素降解的特定但高度冗余的机制。在假定的内切葡聚糖酶中，尤其是迄今未研究的糖苷水解酶家族8的酶很丰富，这表明在纤维素代谢过程中存在一个被忽视的重要作用。此外，这两个物种在纤维素转化过程中都产生了大量丰富的假定蛋白质，为未来的酶学研究提供了丰富的目标宝库。纤维素是地球上最丰富的可再生聚合物，但其难降解性限制了用于能源相关和材料应用的高效转化方法。尽管微生物纤维素转化已经研究了几十年，但最近的进展表明仍然存在很大的知识差距。该门细菌被认为是高效的碳水化合物代谢者，但大多数物种仅限于（半）可溶性聚糖。少数物种，包括土壤细菌哈钦森噬纤维菌和粘液孢囊粘球菌，被认为是纤维素专家，但它们的纤维素分解机制尚不清楚，因为它们不符合当前的酶促纤维素周转模型。通过揭示这两种细菌在结晶纤维素和果胶上生长期间的蛋白质组设置，我们在理解它们独特的纤维素转化模式方面向前迈出了重要一步。本报告为改进生物质转化提供了大量新的酶靶点。
