Ruminococcus torques is a keystone degrader of intestinal mucin glycoprotein, releasing oligosaccharides used by Bacteroides thetaiotaomicron

Symbiotic interactions between humans and our communities of resident gut microbes (microbiota) play many roles in health and disease. Some gut bacteria utilize mucus as a nutrient source and can under certain conditions damage the protective barrier it forms, increasing disease susceptibility. We investigated how Ruminococcus torques—a known mucin-degrader that remains poorly studied despite its implication in inflammatory bowel diseases (IBDs)— degrades mucin glycoproteins or their component O-linked glycans to understand its effects on the availability of mucin-derived nutrients for other bacteria. We found that R. torques utilizes both mucin glycoproteins and released oligosaccharides from gastric and colonic mucins, degrading these substrates with a panoply of mostly constitutively expressed, secreted enzymes. Investigation of mucin oligosaccharide degradation by R. torques revealed strong fucosidase, sialidase and b1,4-galactosidase activities. There was a lack of detectable sulfatase and weak β1,3-galactosidase degradation, resulting in accumulation of glycans containing these structures on mucin polypeptides. While the Gram-negative symbiont, Bacteroides thetaiotaomicron grows poorly on mucin glycoproteins, we demonstrate a clear ability of R. torques to liberate products from mucins, making them accessible to B. thetaiotaomicron. This work underscores the diversity of mucin-degrading mechanisms in different bacterial species and the probability that some species are contingent on others for the ability to more fully access mucin-derived nutrients. The ability of R. torques to directly degrade a variety of mucin and mucin glycan structures and unlock released glycans for other species suggests that it is a keystone mucin degrader, which may contribute to its association with IBD. Ruminococcus torques VIII-239 was grown in 3 biological replicate cultures to mid-log phase under anaerobic conditions at 37ºC on YCFA medium containing either glucose or mucin O-glycans. RNA was isolated and rRNA depleted. RNA-seq analysis was performed to identify differentially regulated genes on these substrates.

人类与常驻肠道微生物群落（gut microbiota）之间的共生互作，在健康与疾病进程中发挥诸多关键作用。部分肠道细菌可利用黏液作为营养源，在特定条件下还会破坏其构成的保护性屏障，提升疾病易感风险。本研究聚焦于迟缓瘤胃球菌（Ruminococcus torques）——一种已被证实与炎症性肠病（inflammatory bowel diseases, IBDs）相关但研究仍较为匮乏的已知黏液降解菌，解析其降解黏液糖蛋白（mucin glycoproteins）及其组分O-连接聚糖（O-linked glycans）的机制，以阐明其对其他细菌获取黏液衍生营养物质的影响。研究发现，迟缓瘤胃球菌可同时利用黏液糖蛋白以及胃、结肠黏液释放的寡糖，并通过一套以组成型表达为主的分泌酶系降解此类底物。对迟缓瘤胃球菌降解黏液寡糖的分析显示，其具备较强的岩藻糖苷酶（fucosidase）、唾液酸酶（sialidase）及β1,4-半乳糖苷酶（b1,4-galactosidase）活性，但未检测到硫酸酯酶（sulfatase）活性，且β1,3-半乳糖苷酶（β1,3-galactosidase）降解能力较弱，最终导致含有此类结构的聚糖在黏液多肽上积累。尽管革兰氏阴性共生菌泰氏拟杆菌（Bacteroides thetaiotaomicron）在黏液糖蛋白上生长能力较差，但本研究证实迟缓瘤胃球菌可从黏液中释放可被泰氏拟杆菌利用的营养产物。本研究凸显了不同细菌物种黏液降解机制的多样性，以及部分物种需依赖其他物种才能更充分获取黏液衍生营养物质的可能性。迟缓瘤胃球菌可直接降解多种黏液及黏液聚糖结构，并为其他物种解锁释放的聚糖，这一特性表明其是一类关键的黏液降解菌，或与其与炎症性肠病的关联存在关联。本研究将迟缓瘤胃球菌VIII-239菌株接种于含葡萄糖或黏液O-连接聚糖的YCFA培养基（YCFA medium）中，于37℃厌氧条件下培养至对数中期，共设置3次生物学重复培养。随后提取总RNA并去除核糖体RNA（rRNA），通过转录组测序（RNA-seq）分析鉴定不同底物下的差异表达基因。