Department of Food Science, Fundamental and Applied Research for Animal and Health, Faculty of Veterinary Medicine, University of Liège, Liège, Belgium.
Laboratory of Probiogenomics, Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, Parma, Italy.
BMC Microbiol. 2020 May 7;20(1):111. doi: 10.1186/s12866-020-01804-9.
Human milk oligosaccharides (HMO) could promote the growth of bifidobacteria, improving young children's health. In addition, fermentation of carbohydrates by bifidobacteria can result in the production of metabolites presenting an antivirulent activity against intestinal pathogens. Bovine milk oligosaccharides (BMO), structurally similar to HMO, are found at high concentration in cow whey. This is particularly observed for 3'-sialyllactose (3'SL). This study focused on enzymes and transport systems involved in HMO/BMO metabolism contained in B. crudilactis and B. mongoliense genomes, two species from bovine milk origin. The ability of B. mongoliense to grow in media supplemented with whey or 3'SL was assessed. Next, the effects of cell-free spent media (CFSM) were tested against the virulence expression of Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium.
Due to the presence of genes encoding β-galactosidases, β-hexosaminidases, α-sialidases and α-fucosidases, B. mongoliense presents a genome more sophisticated and more adapted to the digestion of BMO/HMO than B. crudilactis (which contains only β-galactosidases). In addition, HMO/BMO digestion involves genes encoding oligosaccharide transport systems found in B. mongoliense but not in B. crudilactis. B. mongoliense seemed able to grow on media supplemented with whey or 3'SL as main source of carbon (8.3 ± 1.0 and 6.7 ± 0.3 log cfu/mL, respectively). CFSM obtained from whey resulted in a significant under-expression of ler, fliC, luxS, stx1 and qseA genes (- 2.2, - 5.3, - 2.4, - 2.5 and - 4.8, respectively; P < 0.05) of E. coli O157:H7. CFSM from 3'SL resulted in a significant up-regulation of luxS (2.0; P < 0.05) gene and a down-regulation of fliC (- 5.0; P < 0.05) gene. CFSM obtained from whey resulted in significant up-regulations of sopD and hil genes (2.9 and 3.5, respectively; P < 0.05) of S. Typhimurium, while CFSM obtained from 3'SL fermentation down-regulated hil and sopD genes (- 2.7 and - 4.2, respectively; P < 0.05).
From enzymes and transporters highlighted in the genome of B. mongoliense and its potential ability to metabolise 3'SL and whey, B. mongoliense seems well able to digest HMO/BMO. The exact nature of the metabolites contained in CFSM has to be identified still. These results suggest that BMO associated with B. mongoliense could be an interesting synbiotic formulation to maintain or restore intestinal health of young children.
人乳寡糖（HMO）可以促进双歧杆菌的生长，从而改善幼儿的健康。此外，双歧杆菌对碳水化合物的发酵可以产生具有抗肠道病原体毒力活性的代谢物。牛乳寡糖（BMO）在结构上与 HMO 相似，在牛乳中以高浓度存在。这在 3'-唾液乳糖（3'SL）中尤为明显。本研究集中于 B. crudilactis 和 B. mongoliense 基因组中与 HMO/BMO 代谢相关的酶和转运系统，这两种物种均来自牛乳。评估了 B. mongoliense 在补充乳清或 3'SL 的培养基中生长的能力。接下来，测试了无细胞废弃培养基（CFSM）对大肠杆菌 O157:H7 和肠炎沙门氏菌血清型 Typhimurium 毒力表达的影响。
由于存在编码β-半乳糖苷酶、β-己糖胺酶、α-唾液酸酶和α-岩藻糖苷酶的基因，B. mongoliense 的基因组比 B. crudilactis 更复杂，更适应 BMO/HMO 的消化（B. crudilactis 只含有β-半乳糖苷酶）。此外，HMO/BMO 的消化涉及到在 B. mongoliense 中发现的寡糖转运系统的基因，但在 B. crudilactis 中没有发现。B. mongoliense 似乎能够以乳清或 3'SL 作为主要碳源生长（分别为 8.3±1.0 和 6.7±0.3 log cfu/mL）。从乳清中获得的 CFSM 导致大肠杆菌 O157:H7 的 ler、fliC、luxS、stx1 和 qseA 基因的表达显著下调（分别为-2.2、-5.3、-2.4、-2.5 和-4.8；P<0.05）。从 3'SL 获得的 CFSM 导致 luxS 基因的显著上调（2.0；P<0.05）和 fliC 基因的下调（-5.0；P<0.05）。从乳清中获得的 CFSM 导致 S. Typhimurium 的 sopD 和 hil 基因的显著上调（分别为 2.9 和 3.5；P<0.05），而从 3'SL 发酵中获得的 CFSM 下调了 hil 和 sopD 基因（分别为-2.7 和-4.2；P<0.05）。
从 B. mongoliense 基因组中突出的酶和转运体及其代谢 3'SL 和乳清的潜在能力来看，B. mongoliense 似乎能够很好地消化 HMO/BMO。CFSM 中所含代谢物的确切性质仍有待确定。这些结果表明，与 B. mongoliense 相关的 BMO 可能是一种有趣的共生配方，可以维持或恢复幼儿的肠道健康。
