Department of Animal Sciences and Institute for Genomic Biology, University of Illinois, Urbana, Illinois 61801; email:
Annu Rev Microbiol. 2014;68:279-96. doi: 10.1146/annurev-micro-092412-155618. Epub 2014 Jun 16.
Mammals rely entirely on symbiotic microorganisms within their digestive tract to gain energy from plant biomass that is resistant to mammalian digestive enzymes. Especially in herbivorous animals, specialized organs (the rumen, cecum, and colon) have evolved that allow highly efficient fermentation of ingested plant biomass by complex anaerobic microbial communities. We consider here the two most intensively studied, representative gut microbial communities involved in degradation of plant fiber: those of the rumen and the human large intestine. These communities are dominated by bacteria belonging to the Firmicutes and Bacteroidetes phyla. In Firmicutes, degradative capacity is largely restricted to the cell surface and involves elaborate cellulosome complexes in specialized cellulolytic species. By contrast, in the Bacteroidetes, utilization of soluble polysaccharides, encoded by gene clusters (PULs), entails outer membrane binding proteins, and degradation is largely periplasmic or intracellular. Biomass degradation involves complex interplay between these distinct groups of bacteria as well as (in the rumen) eukaryotic microorganisms.
哺乳动物完全依赖其消化道内的共生微生物，从抵抗哺乳动物消化酶的植物生物质中获取能量。特别是在草食性动物中，已经进化出专门的器官（瘤胃、盲肠和结肠），使复杂的厌氧微生物群落能够高效发酵摄入的植物生物质。在这里，我们考虑了两种最受关注的参与植物纤维降解的代表性肠道微生物群落：瘤胃和人类大肠中的微生物群落。这些群落主要由厚壁菌门和拟杆菌门的细菌组成。在厚壁菌门中，降解能力主要局限于细胞表面，并涉及专门的纤维素分解物种中的复杂纤维素酶复合物。相比之下，在拟杆菌门中，对基因簇 (PULs) 编码的可溶性多糖的利用需要外膜结合蛋白，并且降解主要在周质或细胞内进行。生物质降解涉及这些不同细菌群之间的复杂相互作用，以及（在瘤胃中）真核微生物。
