Horizontal gene transfers differentially shape the functional potential of the infant gut metagenome

Horizontal gene transfer (HGT) is a major driver of microbial evolution, influencing the metabolic potential of microbial communities. Despite its significance, the consequences of HGT in shaping the microbial metabolic potential remain poorly understood, particularly in complex environments such as the human gut. This study aimed to assess the impact of HGT in infant gut microbiome from Caesarean section (CSD) and vaginal delivery (VD) groups during the first year of life. At Month 0, CSD infants exhibited a higher number of HGT events than VD infants. However, the numbers converged around Month 2 and remained comparable until Month 9, with no significant differences between groups (p > 0.05). HGT in VD was primarily driven by Coprococcus catus and Ruminococcus sp_5_1_39BFAA, while in CSD, Salmonella enterica and Klebsiella pneumoniae were dominant donors and acceptors. Functional analysis revealed that HGT in VD enriched genes related to carbohydrate metabolism and immune responses, whereas CSD was enriched for metabolic processes and biofilm formation. Additionally, HGT events were associated with Neonatal Intensive Care Unit Admission and diet transitions. These results suggest that HGT events in the VD and CSD groups differently shape the functional potential of the infant gut microbiome, with possible health implications that require further investigation. However, experimental validation is needed to establish a causal link.