The study investigates how microbes from different maternal body sites shape the infant gut microbiome during the first four months of life. Using strain-resolved metagenomics, researchers tracked microbial transmission from mothers to infants, revealing that the maternal gut microbiome is the primary source of transmitted strains. The infant gut microbiome rapidly develops, with early diversity influenced by niche selection. While maternal skin and vaginal microbes transiently colonize the infant, the maternal gut microbiome persists and is better adapted to the infant gut environment. The study found that the infant gut microbiome is shaped by multiple maternal sources, including the gut, skin, vaginal, oral, and breast milk. Strain-level analysis showed that maternal gut strains are more likely to colonize the infant gut than strains from other sources. The study also identified that some strains are transmitted vertically from mother to infant, with a high rate of strain transmission from the maternal gut. The infant microbiome shows high strain diversity at birth, which decreases over time but gradually increases over the first four months of life. The study highlights the importance of maternal microbiome transmission in shaping the infant microbiome and suggests that the process of microbial colonization is influenced by both environmental and genetic factors. The findings emphasize the role of the maternal gut microbiome in the early development of the infant microbiome and the need for further research into the mechanisms of microbial transmission and colonization.The study investigates how microbes from different maternal body sites shape the infant gut microbiome during the first four months of life. Using strain-resolved metagenomics, researchers tracked microbial transmission from mothers to infants, revealing that the maternal gut microbiome is the primary source of transmitted strains. The infant gut microbiome rapidly develops, with early diversity influenced by niche selection. While maternal skin and vaginal microbes transiently colonize the infant, the maternal gut microbiome persists and is better adapted to the infant gut environment. The study found that the infant gut microbiome is shaped by multiple maternal sources, including the gut, skin, vaginal, oral, and breast milk. Strain-level analysis showed that maternal gut strains are more likely to colonize the infant gut than strains from other sources. The study also identified that some strains are transmitted vertically from mother to infant, with a high rate of strain transmission from the maternal gut. The infant microbiome shows high strain diversity at birth, which decreases over time but gradually increases over the first four months of life. The study highlights the importance of maternal microbiome transmission in shaping the infant microbiome and suggests that the process of microbial colonization is influenced by both environmental and genetic factors. The findings emphasize the role of the maternal gut microbiome in the early development of the infant microbiome and the need for further research into the mechanisms of microbial transmission and colonization.