Genome-wide screen for Escherichia coli genes involved in repressing cell-to-cell transfer of a nonconjugative pSC101-derived plasmid

Acquiring new genetic traits by lateral gene transfer is a bacterial strategy for environmental adaptations. We previously showed that Escherichia coli laterally transmits nonconjugative plasmids in cocultures that contain strains with or without the plasmid. Using a pMB1-derived plasmid and the Keio collection, a comprehensive library of E. coli knockout mutants for nonessential genes, we recently screened for genes responsible for promoting or repressing cell-to-cell plasmid transfer in recipient cells. In this study, we used a pSC101-derived plasmid, instead of a pMB1-derived plasmid, to screen for repressing genes and identified 29 “transfer-up” mutants. Among these, four mutants are common to those previously screened using a pMB1-derived plasmid. Although the roles of the 29 gene products in plasmid transfer mechanism remain uncertain, it is interesting that 28 of the 29 screened genes map to two limited regions on the E. coli chromosome: 18 genes at 34.25–35.31 min and 10 genes at 12.62–13.35 min. Because these two regions commonly contain termination (Ter) sites for DNA replication (TerC: 34.64 min and TerH: 12.91 min), it is possible that chromosomal mutations around specific Ter sites may affect plasmid acquisition in the recipient cells.