Rôle du système de sécrétion de Type IV dans la formation de biofilms chez Caulobacter crescentus

Abstract

Bacteria have always been considered as individual cells, not being capable of complex behaviors. This simplistic view of bacterial life has evolved and today it is known that bacteria are able to communicate with each other (Quorum Sensing) and live together (biofilms). Biofilm is defined as a community of bacteria attached to a surface and surrounded by an extracellular matrix produced by the bacteria themselves. This matrix is composed of various elements such as exopolysaccharides, proteins or DNA. Interest in the study of biofilms has become increasingly important due to their involvement in many issues related to public health. Indeed, biofilms confer increased resistance to bacteria in the face of physical forces, treatment with antibiotics and even against the host immune system. This resistance is multifactorial mainly due to the presence of the extracellular matrix of biofilms containing structural proteins and enzymes that allow the formation and maintenance of these “cities of microbes.” At present, the mechanisms that regulate the secretion of this matrix component substrates are unknown. In this work, we demonstrated that in the aquatic bacteria, Caulobacter crescentus, Type IV secretion system (T4SS), often known as a virulence factor in many pathogenic bacteria such as Brucella melitensis, Bordetella pertussis and Agrobacterium tumefaciens, was involved in proteins secretion allowing the formation of biofilms. One such protein is an enzyme of the Krebs cycle, isocitrate dehydrogenase whose activity appears to be important in the early stages of development of biofilms. Interestingly, our model can be extrapolated to other bacteria with different lifestyles as Sinorhizobium meliloti and in lesser effect, A. tumefaciens, suggesting conservation of function of the T4SS throughout evolution. Our results suggest for the first time the presence of an active secretion process controlling biofilm formation and also a new role for the T4SS.

Date of Award	26 Apr 2012
Original language	French
Awarding Institution	University of Namur
Supervisor	Xavier De Bolle (Co-Supervisor), Jean-Yves Matroule (Supervisor), JEAN-JACQUES LETESSON (Jury), Christophe Dehio (Jury), Jan MICHIELS (Jury), Sébastien RIGALI (Jury) & Laurence Van Melderen (Jury)