Characterization and global gene expression of F- phenocopies during Escherichia coli biofilm formation.

The ecological role of horizontal gene transfer within biofilms has been recently investigated, and it has been reported that conjugation directly induces bacteria to form biofilms via expression of conjugative pili. In this report, we described the contribution of bacterial conjugation during biofilm formation by Escherichia coli harboring a natural IncF conjugative F plasmid (F(+)). We showed that cell-to-cell pili interactions through the homosexual mating-pair formation among F(+) × F(+) cells (namely, F(-) phenocopy phenomenon) promote E. coli biofilm formation at the early development stage. The presence of F(+) × F(+) population is the result from heterogeneity within biofilms leading to sessile bacteria that grow at different rates, in which the late-stationary phase cells acted as F(-) phenocopy cells. According to global transcriptional analysis, the biofilm lifestyle shared similar gene expression pattern with F(-) phenocopies. F(-) phenocopy cells expressed specific sets of chromosomal genes (e.g., genes for general stress response and two-component systems) that control the regulation regions of F transfer operon by blocking surface exclusion proteins and DNA transfer machineries. However, mating-pair proteins were stabilized and consequently promoted F(+) × F(+) pili assembly. Thus, F(-) phenocopy phenomenon is an effective adaptive behavior of bacterial cells during biofilm formation.