Novel Plasmid-Borne Fimbriae-Associated Gene Cluster Participates in Biofilm Formation in Escherichia coli

This study reported the involvement of a gene cluster from a conjugative plasmid in the biofilm formation of Escherichia coli. We used a novel EZ-Tn5 transposon technique to generate a transposon library and used arbitrarily primed PCR to detect the insertion sites in biofilm formation-deficient mutants. To validate the function of candidate biofilm formation genes, the genes were cloned into plasmid pBluescript II SK (+) and transformed into E. coil DH5 alpha. Biofilm production from the transformants was then assessed by phenotypic biofilm formation using Crystal Violet staining and microscopy. A total of 3,000 transposon mutants of E. coli DH5 alpha-p253 were screened, of which 28 were found to be deficient in biofilm formation. Further characterization revealed that 24/28 mutations were detected with their insertions in chromosome, while the remaining 4 mutations were evidenced that the functional genes for biofilm formation were harbored in the plasmid. Interestingly, the plasmid sequencing showed that these four transposon mutations were all inserted into a fimbriae-associated gene cluster (fim-cluster). This fim-cluster is a hybrid segment spanning a 7,949 bp sequence, with a terminal inverted repeat sequence and two coding regions. In summary, we performed a high-efficiency screening to a library constructed with the EZ-Tn5-based transposon approach and identified the gene clusters responsible for the biofilm production of E. coli, especially the genes harbored in the plasmid. Further studies are needed to understand the spread of this novel plasmid-mediated biofilm formation gene in clinical E. coli isolates and the clinical impacts.