CCL2 and colitis: Of note, we found that depletion of anaerobic bacteria in early life by metronidazole also leads to further exacerbated DSS-induced colitis in mice, as indicated by aggravated body weight loss (Fig. S7D), increased mortality (Fig. S7E and F), destruction of the epithelial architecture (Fig. S7G), and upregulated mRNA levels of inflammatory cytokines (Tnf-α, IL-6, and IL-1β) and chemokines (Cxcl1, Ccl2, and Ccl3) (Fig. S7J and K).