Milk fat globule membrane protects Bifidobacterium longum ssp. infantis ATCC 15697 against bile stress by modifying global transcriptional responses

Milk fat globule membrane (MFGM) can protect probiotic bacteria from bile stress. However, its potential mechanism has not been reported. We studied that the viability, morphology and gene transcriptional response of Bifidobacterium longum subsp. infantis ATCC 15697 (BI_15697) stressed by bile salts with or without MFGM. It was shown that MFGM alleviated the reduction in BI_15697 population induced by 0.2% porcine bile stress and restored the population to the control levels. MFGM ameliorated the shrunken, fragmented appearance and irregular morphology of BI_15697 and maintained cell integrity disrupted by bile stress. RNA-seq results showed that MFGM increased transport of glucose and raffinose and decreased that of branched-chain amino acids (BCAA) in the presence of bile salts. MFGM stimulated the expression of genes involved in the synthesis of raffinose in galactose metabolism and the metabolism of BCAA, suggesting that MFGM stimulated the accumulation of raffinose and BCAA in the presence of bile. In addition, MFGM stimulated the expression of two bile efflux transporters under bile stress. Together, the multifactorial response helps BI_15697 excrete bile salts and maintain cellular integrity in response to bile stress. Seven supplementary tables was presented here for this paper.

乳脂肪球膜（Milk fat globule membrane, MFGM）可保护益生菌免受胆汁胁迫。然而，其潜在作用机制尚未见报道。本研究探究了在添加与不添加乳脂肪球膜的情况下，经胆汁盐胁迫处理的长双歧杆菌婴儿亚种ATCC 15697（BI_15697）的活菌活性、菌体形态及基因转录响应。结果显示，乳脂肪球膜可缓解0.2%猪源胆汁盐胁迫导致的BI_15697菌群数量降低，并将其恢复至对照组水平。乳脂肪球膜可改善BI_15697出现的皱缩、破碎及形态异常表型，维持胆汁胁迫所破坏的细胞完整性。RNA测序（RNA-seq）结果表明，在胆汁盐存在的条件下，乳脂肪球膜可促进葡萄糖与棉子糖的转运，同时抑制支链氨基酸（branched-chain amino acids, BCAA）的转运。乳脂肪球膜可激活半乳糖代谢通路中参与棉子糖合成的基因以及支链氨基酸代谢相关基因的表达，提示其可在胆汁胁迫环境下促进BI_15697内棉子糖与支链氨基酸的积累。此外，乳脂肪球膜可在胆汁胁迫下上调两种胆汁外排转运蛋白的表达。综上，这种多因素响应可帮助BI_15697排出胆汁盐并维持细胞完整性，以应对胆汁胁迫。本文附带7张补充表格。