Department of Biological Chemistry, The Weizmann Institute of Science, Rehovot, Israel.
BMC Genomics. 2012 May 30;13:210. doi: 10.1186/1471-2164-13-210.
Microbial degradation of plant cell walls and its conversion to sugars and other byproducts is a key step in the carbon cycle on Earth. In order to process heterogeneous plant-derived biomass, specialized anaerobic bacteria use an elaborate multi-enzyme cellulosome complex to synergistically deconstruct cellulosic substrates. The cellulosome was first discovered in the cellulolytic thermophile, Clostridium thermocellum, and much of our knowledge of this intriguing type of protein composite is based on the cellulosome of this environmentally and biotechnologically important bacterium. The recently sequenced genome of the cellulolytic mesophile, Acetivibrio cellulolyticus, allows detailed comparison of the cellulosomes of these two select cellulosome-producing bacteria.
Comprehensive analysis of the A. cellulolyticus draft genome sequence revealed a very sophisticated cellulosome system. Compared to C. thermocellum, the cellulosomal architecture of A. cellulolyticus is much more extensive, whereby the genome encodes for twice the number of cohesin- and dockerin-containing proteins. The A. cellulolyticus genome has thus evolved an inflated number of 143 dockerin-containing genes, coding for multimodular proteins with distinctive catalytic and carbohydrate-binding modules that play critical roles in biomass degradation. Additionally, 41 putative cohesin modules distributed in 16 different scaffoldin proteins were identified in the genome, representing a broader diversity and modularity than those of Clostridium thermocellum. Although many of the A. cellulolyticus scaffoldins appear in unconventional modular combinations, elements of the basic structural scaffoldins are maintained in both species. In addition, both species exhibit similarly elaborate cell-anchoring and cellulosome-related gene- regulatory elements.
This work portrays a particularly intricate, cell-surface cellulosome system in A. cellulolyticus and provides a blueprint for examining the specific roles of the various cellulosomal components in the degradation of complex carbohydrate substrates of the plant cell wall by the bacterium.
微生物对植物细胞壁的降解及其转化为糖和其他副产品是地球碳循环的关键步骤。为了处理异质的植物衍生生物质，专门的厌氧菌使用复杂的多酶纤维素体复合物协同地解构纤维素基质。纤维素体最初在纤维素分解嗜热菌 Clostridium thermocellum 中被发现，我们对这种引人入胜的蛋白质复合物的大部分了解都是基于这种具有环境和生物技术重要性的细菌的纤维素体。最近测序的纤维素分解中温菌 Acetivibrio cellulolyticus 的基因组，允许对这两种选择的纤维素产生菌的纤维素体进行详细比较。
对 A. cellulolyticus 草图基因组序列的综合分析揭示了一个非常复杂的纤维素体系统。与 C. thermocellum 相比，A. cellulolyticus 的纤维素体结构要广泛得多，基因组编码的粘着蛋白和 dockerin 蛋白数量是前者的两倍。因此，A. cellulolyticus 基因组进化出了大量的 143 个 dockerin 基因，这些基因编码具有独特催化和碳水化合物结合模块的多模块蛋白，这些模块在生物质降解中起着关键作用。此外，在基因组中还鉴定出 41 个推定的粘着蛋白模块，分布在 16 种不同的支架蛋白中，这代表了比 Clostridium thermocellum 更广泛的多样性和模块化。尽管 A. cellulolyticus 的许多支架蛋白似乎存在于非常规的模块化组合中，但这两种物种的基本结构支架蛋白的元素都得以保留。此外，这两种物种都表现出类似精细的细胞锚定和纤维素体相关基因调控元件。
这项工作描绘了 A. cellulolyticus 中一个特别复杂的细胞表面纤维素体系统，并为研究各种纤维素体成分在细菌降解植物细胞壁复杂碳水化合物底物中的具体作用提供了蓝图。
