Study of the interaction between plasmid conjugation and bacterial capsules

Bacterial evolution is influenced by mobile genetic elements (MGE) like phages and plasmids, which can provide adaptive traits but also have fitness costs. The bacterial capsule affects MGE infection, but its importance is difficult to quantify due to genomic diversity and confounding mechanisms. We swapped capsule loci in Klebsiella pneumoniae to study their effect on plasmid and phage transfer. Capsule swaps revealed that serotypes are key determinants of phage infection. Capsule types also affect conjugation efficiency, shaped by capsule volume and pilus structure. Comparative genomics confirmed that permissive serotypes in the lab acquire more plasmids in nature. Pili least sensitive to capsules (F-like) are most frequent in species' plasmids, associated with antibiotic resistance and virulence factors, driving convergence between virulence and antibiotic resistance. Results highlight how cellular envelope traits influence infection by mobile genetic elements, with implications for population dynamics and gene transfer.