Microbiology Group, The Rowett Institute, University of Aberdeen, Aberdeen, UK.
Department of Biomolecular Sciences, The Weizmann Institute of Science, Rehovot, Israel.
Environ Microbiol. 2018 Jan;20(1):324-336. doi: 10.1111/1462-2920.14000. Epub 2017 Dec 7.
Ruminococcus bromii is a dominant member of the human colonic microbiota that plays a 'keystone' role in degrading dietary resistant starch. Recent evidence from one strain has uncovered a unique cell surface 'amylosome' complex that organizes starch-degrading enzymes. New genome analysis presented here reveals further features of this complex and shows remarkable conservation of amylosome components between human colonic strains from three different continents and a R. bromii strain from the rumen of Australian cattle. These R. bromii strains encode a narrow spectrum of carbohydrate active enzymes (CAZymes) that reflect extreme specialization in starch utilization. Starch hydrolysis products are taken up mainly as oligosaccharides, with only one strain able to grow on glucose. The human strains, but not the rumen strain, also possess transporters that allow growth on galactose and fructose. R. bromii strains possess a full complement of sporulation and spore germination genes and we demonstrate the ability to form spores that survive exposure to air. Spore formation is likely to be a critical factor in the ecology of this nutritionally highly specialized bacterium, which was previously regarded as 'non-sporing', helping to explain its widespread occurrence in the gut microbiota through the ability to transmit between hosts.
布罗梭瘤胃球菌是人类结肠微生物群的主要成员，它在降解膳食纤维方面发挥着“基石”作用。最近来自于一个菌株的证据揭示了一个独特的细胞表面“淀粉体”复合物，它组织了淀粉降解酶。本文呈现的新基因组分析进一步揭示了这个复合物的特征，并显示了来自三个不同大陆的人类结肠菌株和来自澳大利亚牛瘤胃的布罗梭瘤胃球菌菌株之间淀粉体成分的惊人保守性。这些布罗梭瘤胃球菌菌株编码窄谱碳水化合物活性酶（CAZymes），反映了其在淀粉利用方面的极端专业化。淀粉水解产物主要被吸收为低聚糖，只有一个菌株能够以葡萄糖为生长基质。人类菌株，但不是瘤胃菌株，也拥有允许其在半乳糖和果糖上生长的转运蛋白。布罗梭瘤胃球菌菌株拥有完整的孢子形成和孢子萌发基因，我们证明了其形成能够耐受空气暴露的孢子的能力。孢子形成可能是这种营养高度专业化细菌的生态学中的一个关键因素，它以前被认为是“非孢子形成的”，通过在宿主间传播的能力有助于解释其在肠道微生物群中的广泛存在。
