The human gastrointestinal tract is colonized by an extraordinarily dense and diverse community of microorganisms, collectively termed the gut microbiome. This intricate ecosystem comprises trillions of bacteria, archaea, viruses, fungi, and parasites, with bacteria being the most abundant and well-studied component, encompassing over a thousand distinct species. This "microscopic world within" is primarily concentrated in the large intestine and is unique to everyone. Its initial establishment is heavily influenced by maternal factors during vaginal delivery and breastfeeding, followed by continuous modulation throughout life by factors such as diet and other environmental exposures.