Type 4 pili mediated natural competence in Fusobacterium nucleatum

Many bacterial species naturally take up DNA from their surroundings and recombine it into their chromosome through homologous gene transfer (HGT) to aid in survival and gain advantageous functions. Herein we present the first characterization of Type 4 pili mediated natural competence in Fusobacterium nucleatum, which are Gram-negative, anaerobic bacteria that participate in a range of infections and diseases including periodontitis, preterm birth, and cancer. We bioinformatically identified components of the Type 4 conjugal pilus machinery and show this is a conserved system within the Fusobacterium genus. We next validate Type 4 pili in natural competence in F. nucleatum strain 23726 and show that gene deletions in key components of pilus deployment (pilQ) and cytoplasmic DNA import (comEC) abolish DNA uptake and chromosomal incorporation. We next show that natural competence may require native F. nucleatum DNA methylation to bypass restriction modification systems and allow subsequent genomic homologous recombination. In summary, this proof of principle study provides the first characterization of natural competence in Fusobacterium nucleatum and highlights the potential to exploit this DNA import mechanism as a genetic tool to characterize virulence mechanisms of an opportunistic oral pathogen.