Weimer Paul J
Department of Bacteriology, University of Wisconsin, Madison, WI 53706, USA.
Microorganisms. 2022 Nov 27;10(12):2345. doi: 10.3390/microorganisms10122345.
As major structural components of plant cell walls, cellulose and hemicellulose are degraded and fermented by anaerobic microbes in the rumen to produce volatile fatty acids, the main nutrient source for the host. Cellulose degradation is carried out primarily by specialist bacteria, with additional contributions from protists and fungi, via a variety of mechanisms. Hemicelluloses are hydrolyzed by cellulolytic bacteria and by generalist, non-cellulolytic microbes, largely via extracellular enzymes. Cellulose hydrolysis follows first-order kinetics and its rate is limited by available substrate surface area. Nevertheless, its rate is at least an order of magnitude more rapid than in anaerobic digesters, due to near-obligatory adherence of microbial cells to the cellulose surface, and a lack of downstream inhibitory effects; in the host animal, fiber degradation rate is also enhanced by the unique process of rumination. Cellulolytic and hemicellulolytic microbes exhibit intense competition and amensalism, but they also display mutualistic interactions with microbes at other trophic levels. Collectively, the fiber-degrading community of the rumen displays functional redundancy, partial niche overlap, and convergence of catabolic pathways that all contribute to stability of the ruminal fermentation. The superior hydrolytic and fermentative capabilities of ruminal fiber degraders make them promising candidates for several fermentation technologies.
作为植物细胞壁的主要结构成分，纤维素和半纤维素在瘤胃中被厌氧微生物降解和发酵，产生挥发性脂肪酸，这是宿主的主要营养来源。纤维素降解主要由专门的细菌进行，原生生物和真菌也通过多种机制做出额外贡献。半纤维素主要通过细胞外酶被纤维素分解细菌和非纤维素分解的普通微生物水解。纤维素水解遵循一级动力学，其速率受可用底物表面积限制。然而，由于微生物细胞几乎必然会附着在纤维素表面，且不存在下游抑制作用，其速率至少比厌氧消化器快一个数量级；在宿主动物中，反刍这一独特过程也提高了纤维降解速率。纤维素分解和半纤维素分解微生物表现出激烈的竞争和偏害共生，但它们也与其他营养级的微生物表现出互利共生关系。总体而言，瘤胃中的纤维降解群落表现出功能冗余、部分生态位重叠以及分解代谢途径的趋同，所有这些都有助于瘤胃发酵的稳定性。瘤胃纤维降解菌卓越的水解和发酵能力使其成为多种发酵技术的理想候选者。
