Extracellular proteins are important factors in host-microbe interactions; however, the specific factors that enable bifidobacterial adhesion and survival in the gastrointestinal (GI) tract are not fully characterized. Here, we discovered that Bifidobacterium longum NCC2705 cultured in bacterium-free supernatants of human fecal fermentation broth released a myriad of particles into the extracellular environment. The aim of this study was to characterize the physiological properties of these extracellular particles. The particles, approximately 50 to 80 nm in diameter, had high protein and double-stranded DNA contents, suggesting that they were extracellular vesicles (EVs). A proteomic analysis showed that the EVs primarily consisted of cytoplasmic proteins with crucial functions in essential cellular processes. We identified several mucin-binding proteins by performing a biomolecular interaction analysis of phosphoketolase, GroEL, elongation factor Tu (EF-Tu), phosphoglycerate kinase, transaldolase (Tal), and heat shock protein 20 (Hsp20). The recombinant GroEL and Tal proteins showed high binding affinities to mucin. Furthermore, the immobilization of these proteins on microbeads affected the permanence of the microbeads in the murine GI tract. These results suggest that bifidobacterial exposure conditions that mimic the intestine stimulate B. longum EV production. The resulting EVs exported several cytoplasmic proteins that may have promoted B. longum adhesion. This study improved our understanding of the Bifidobacterium colonization strategy in the intestinal microbiome.

中文翻译：

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长双歧杆菌产生的细胞外囊泡输出粘蛋白结合蛋白。

细胞外蛋白是宿主与微生物相互作用的重要因素。但是，使双歧杆菌粘附并在胃肠道（GI）存活的特定因素尚未完全表征。在这里，我们发现长双歧杆菌在人粪便发酵液的无细菌上清液中培养的NCC2705将无数颗粒释放到细胞外环境中。这项研究的目的是表征这些细胞外颗粒的生理特性。直径约50至80 nm的颗粒具有高蛋白质和双链DNA含量，表明它们是细胞外囊泡（EVs）。蛋白质组学分析表明，电动汽车主要由在关键细胞过程中具有关键功能的胞质蛋白组成。我们通过进行磷酸酮醇酶，GroEL，延伸因子Tu（EF-Tu），磷酸甘油酸酯激酶，转醛醇酶（Tal）和热休克蛋白20（Hsp20）的生物分子相互作用分析，鉴定了几种黏蛋白结合蛋白。重组GroEL和Tal蛋白显示出对粘蛋白的高结合亲和力。此外，这些蛋白质在微珠上的固定影响了鼠胃肠道中微珠的持久性。这些结果表明，模仿肠道的双歧杆菌暴露条件会刺激B. longum EV生产。所得的电动汽车输出了可能促进长双歧杆菌粘附的几种胞质蛋白。这项研究提高了我们对肠道微生物组中双歧杆菌定殖策略的了解。