Complex sentence: The gut microbiota are essential for normal development and homeostasis of the immune system in the gut, modulate epithelial cell proliferation, protect against pathogenic bacteria, and modulate villus architecture and angiogenesis within the intestine.
Split into simpler sentences: The gut microbiota are essential for normal development and homeostasis of the immune system in the gut. They modulate epithelial cell proliferation, protect against pathogenic bacteria, and modulate villus architecture and angiogenesis within the intestine.