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REGULATION OF SURFACE ADHESION AND BIOFILM FORMATION

We hypothesized that commensal and pathogenic E. coli could possess a partly unexplored arsenal of surface adhesins contributing to colonization and biofilm maturation under specific environmental conditions. We explored the cryptic adhesion potential of both commensal and pathogenic E. coli species using genetic approaches developed in our laboratory.

• Regulation of the expression of cryptic fimbriae in Escherichia coli

Type I fimbriae are surface fimbriae involved in bladder colonization and biofilm formation in various E. coli, including uropathogenic E. coli. We characterized seven E. coli K-12 operons (ycb, ybg, yfc, yad, yra, sfm and yeh) encoding for type 1 fimbriae homologues. We showed that these fimbriae are under the negative control of H-NS repressor but are otherwise fully functional, with sugar binding specificities that are distinct from mannose affinity described for type 1 fimbriae.

This study further extend the known diversity of commensal and pathogenic E. coli adhesion arsenal. The distinct substrate specificities of these fimbriae suggests that they could be involved in E. coli tissue tropism contributing to bacterial ability to adapt and colonize a variety of surfaces in different environments.

Korea, C. G., Badouraly, R., Prevost, M. C., Ghigo, J. M. and Beloin, C. (2010) Escherichia coli K-12 possesses multiple cryptic but functional chaperone-usher fimbriae with distinct surface specificities  Environ Microbiol.12:1957-77.

• Korea, C.; J. M. Ghigo and C. Beloin. (2011) The sweet connection: solving the riddle of multiple sugar-binding fimbrial adhesins in Escherichia coli Bioessays . vol. 33 (4) pp. 300-11.

• Functional analysis of new autotransporters adhesins in Escherichia coli

collaboration with M. Schembri, University of Queensland, Australia.

Autotransporters are secreted proteins with functions ranging from adhesins, proteases and hydrolytic enzymes. In collaboration with M. Schembri, (University of Queensland, Australia), we characterized several cryptic homologues of the self-recognizing autotransporter adhesin antigen 43 (Ag43) in the uropathogenic E. coli CFT073. In-depth molecular analysis of these cryptic cell surface autotransporter adhesins showed that they contribute to biofilm formation, binding to ECM proteins and long-term in vivo persistence and colonization of the mouse bladder.

Our findings revealed the existence of pathogenicity-adapted variants of Ag43 previously considered as cryptic, with distinct virulence-related functions.

•Allsopp, L.P.; Beloin, C.; Totsika, M.;  Ghigo, J.M. and M.A. Schembri. Functional heterogeneity of the UpaH autotransporter protein from uropathogenic Escherichia coli. J. Bacteriol in press.

•Allsopp, L.P. ; Beloin, C., Ulett, G.C. ;Valle, J ; Totsika, M. ; Sherlock, O., Ghigo, J.M. and M.A. Schembri. (2012) Molecular Characterisation of UpaB and UpaC - two new Autotransporter Proteins of Uropathogenic Escherichia coli CFT073. Infection and Immunity 80(1):321-32.

Valle, J., Mabbett, A. N., Ulett, G. C., Toledo-Arana, A., Wecker, K., Totsika, M., Schembri, M. A., Ghigo, J. M. and Beloin, C. (2008) UpaG, a new member of the trimeric autotransporter family of adhesins in uropathogenic Escherichia coli  J Bacteriol.190:4147-61.

• Ulett, G.C.; Valle, J. ; Beloin, C. ; Sherlock, O; Ghigo, J.M. and M.A. Schembri. (2007). Functional analysis of Antigen 43 in uropathogenic Escherichia coli reveals a role in long term persistence in the urinary tract. Infection and Immunity 75 3233-3244

Roux, A., Beloin, C. and Ghigo, J. M. (2005) Combined Inactivation and Expression Strategy To Study Gene Function under Physiological Conditions: Application to Identification of New Escherichia coli Adhesins  J Bacteriol.187:1001-13.

• Regulation

Role of the transcriptional regulator RfaH in the unmasking of cell surface adhesin in Escherichia coli

The  capacity of pathogenic bacteria to form biofilm is often considered as a virulence determinant. However, the link between biofilm and bacterial virulence is poorly understood. The influence on biofilm formation of different global virulence regulators has been analyzed in both uropathogenic and commensal Escherichia coli. We showed that RfaH, a positive regulator of the expression of several E. coli virulence-associated genes, is also a repressor of biofilm formation in E. coli. RfaH acts through the regulation of the surface presentation of known as well as new surface adhesins.

Since the expression of several E. coli virulence-associated genes depends on RfaH, our study provides evidence that biofilm formation and virulence gene expression can be mutually exclusive processes. Biofilm formation may therefore not be considered only as a virulence trait per se but rather as a mechanism by which bacteria can finely tune their virulence properties in response to environmental signals.

C. Beloin, K. Michaelis, K. Lindner, P. Landini, J. Hacker, J. M. Ghigo and U. Dobrindt. (2006) The Transcriptional Antiterminator RfaH Represses Biofilm Formation in Escherichia coli J Bacteriol.188:1316-31.






























CELL ENVELOPE PROTEINS INVOLVED IN BIOFILM FORMATION

Biofilm adhesins in Salmonella

BapA, a large secreted protein required for biofilm formation and host colonization of Salmonella enterica serovar Enteritidis

In this study realized in a collaboration led by Inigo Lasa’s laboratory (Pamplona, Spain), we demonstrated that the protein encoded by the gene stm2689 is required for air–broth interface pellicle and biofilm formation. We also provide evidence that Stm2689, renamed as BapA due to significant similarities with the S. aureus Bap protein, plays a role in colonization of the murine intestine and subsequent organ invasion. The presence of surface proteins exhibiting homology with the Bap protein of S. aureus seems therefore widespread among diverse bacterial species (see also). This suggests that the Bap proteins are required for an important and conserved function in bacterial biofilm development.

Latasa,C. Roux, A.  Toledo-Arana, A. ; Ghigo, J.M. ;Gamazo, C. Penadés, J.  and I.Lasa (2005) BapA, a large secreted protein required for biofilm formation and host colonization of Salmonella enterica serovar Enteritidis . Mol Microbiol. 58 :1322-1340.