Pili are essential for conjugation also in many Gram-positive bacteria

Type IV secretion systems (T4SS) enable the spread of antibiotic resistance and other virulence factors. In Gram-positive bacteria, T4SSs have long been thought to lack VirB2-like proteins that form conjugative pili and instead rely on adhesins for cell-cell contacts. Yet, it has remained unclear how subsequent DNA transfer (conjugation) is physically mediated. Here we identify a VirB2-like protein, PrgFB2, from the clinically isolated conjugative plasmid pCF10 in Enteroccocus faecalis and show that it is essential for conjugation. Structural modeling confidently predicts a pilus-like assembly for PrgFB2. We validate this prediction through mutagenesis, conjugation assays, and targeted chemical labeling. By combining various machine learning bioinformatic techniques, we analysed >1000 Gram-positive conjugative plasmids from diverse species, including major pathogens, and identified pili forming VirB2-like proteins in almost all of them. Our findings overturn the prevailing view that Gram-positive T4SSs lack pili. This discovery provides a new framework for understanding horizontal gene transfer and highlights critical targets for combating antimicrobial resistance and virulence in Gram-positive bacteria.