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Journal of Bacteriology, November 2008, p. 7479-7490, Vol. 190, No. 22
0021-9193/08/$08.00+0     doi:10.1128/JB.00823-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Escherichia coli Harboring a Natural IncF Conjugative F Plasmid Develops Complex Mature Biofilms by Stimulating Synthesis of Colanic Acid and Curli ^,

Thithiwat May and Satoshi Okabe^*

Graduate School of Engineering, Hokkaido University, Kita-13, Nishi-8, Kita-Ku, Sapporo 060-8628, Japan

Received 12 June 2008/ Accepted 29 August 2008

It has been shown that Escherichia coli harboring the derepressed IncFI and IncFII conjugative F plasmids form complex mature biofilms by using their F-pilus connections, whereas a plasmid-free strain forms only patchy biofilms. Therefore, in this study we investigated the contribution of a natural IncF conjugative F plasmid to the formation of E. coli biofilms. Unlike the presence of a derepressed F plasmid, the presence of a natural IncF F plasmid promoted biofilm formation by generating the cell-to-cell mating F pili between pairs of F⁺ cells (approximately two to four pili per cell) and by stimulating the formation of colanic acid and curli meshwork. Formation of colanic acid and curli was required after the initial deposition of F-pilus connections to generate a three-dimensional mushroom-type biofilm. In addition, we demonstrated that the conjugative factor of F plasmid, rather than a pilus synthesis function, was involved in curli production during biofilm formation, which promoted cell-surface interactions. Curli played an important role in the maturation process. Microarray experiments were performed to identify the genes involved in curli biosynthesis and regulation. The results suggested that a natural F plasmid was more likely an external activator that indirectly promoted curli production via bacterial regulatory systems (the EnvZ/OmpR two-component regulators and the RpoS and HN-S global regulators). These data provided new insights into the role of a natural F plasmid during the development of E. coli biofilms.

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* Corresponding author. Mailing address: Graduate School of Engineering, Hokkaido University, Kita-13, Nishi-8, Kita-Ku, Sapporo 060-8628, Japan. Phone and fax: 81-(0)11-706-6266. E-mail: sokabe{at}eng.hokudai.ac.jp

Published ahead of print on 12 September 2008.

Supplemental material for this article may be found at http://jb.asm.org/.

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Journal of Bacteriology, November 2008, p. 7479-7490, Vol. 190, No. 22
0021-9193/08/$08.00+0     doi:10.1128/JB.00823-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

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