S100A9 and inflammatory bowel disease: To get deeper insights into the effects of host inflammation-associated proteins (S100A8, S100A9, IL-1β, and TNF-α) on gut bacteria, we further investigated the proteome response of four representative species relevant to IBD, including B. vulgatus, whose proteases link with UC disease severity [46], Bifidobacterium adolescentis, a SCFA producer decreased in IBD [3], Enterocloster bolteae, and Ruminococcus gnavus, which is associated with CD [47].