The present application includes two projects of Microbial Pathogenesis: type III
secretion (T3S) in the Yersinia archetype (A) and Capnocytophaga canimorsus (Cc)
(B). The T3S project deals with the assembly an operation of a bacterial
nanomachine. The Cc project deals with evasion from innate immunity.
A. Type III secretion
T3S allows pathogenic Gram-negative bacteria to deliver bacterial effector proteins
straight into the cytosol of an eukaryotic host cell (1). Translocation of the effectors is
a very rapid process (5), triggered by host cell contact (4) and achieved in one step
by a nanomachine called the injectisome (2, 3). The injectisome ends up with a
needle, protruding from the bacterial surface. Its operation involves the insertion of a
pore, made by proteins called translocators, into the target cell membrane (1).
The first questions we want to address concern the mechanism of needle length
control. Length control is a very basic problem in Biology. Our observation that YscP
acts as a molecular ruler shed new light on this question but, as usual raises a
number of questions which we like to try to address now. The second aspect we will
investigate is the assembly and structure of the translocation pore, as well as its
relation to the needle. The third aspect is the deciphering of the assembly
mechanism of the distal part of the injectisome. This will involve a classical
molecular biology approach, a structural approach and a proteomic approach.
Finally, we would like to tackle the question of the trigger mechanism, essentially by
investigating the link between the YopN complex and LcrG and determining whether
Ca2+ ions could play a role in the stability of this complex.
1.Cornelis, G. R., and H. Wolf-Watz. 1997. Mol Microbiol 23:861-7.
2.Kubori, T., Y. Matsushima, D. Nakamura, J. Uralil, M. Lara-Tejero, A. Sukhan, J. E. Galan, and S. I.
Aizawa. 1998. Science 280:602-5.
3.Mueller, C. A., P. Broz, S. A. Muller, P. Ringler, F. Erne-Brand, I. Sorg, M. Kuhn, A. Engel, and G. R.
Cornelis. 2005. Science 310:674-6.
4.Pettersson, J., R. Nordfelth, E. Dubinina, T. Bergman, M. Gustafsson, K. E. Magnusson, and H. Wolf-
Watz. 1996. Science 273:1231-3.
5.Schlumberger, M. C., A. J. Muller, K. Ehrbar, B. Winnen, I. Duss, B. Stecher, and W. D. Hardt. 2005.
Proc Natl Acad Sci U S A 102:12548-53.
B. Capnocytophaga canimorsus
Capnocytophaga canimorsus is a slow-growing Gram-negative bacterium that is
commonly found in dog's mouths and increasingly isolated from severe infections
following dog bites or scratches. Septicaemia and meningitis with high mortality are
the most commonly reported syndromes. Most of the infections are reported in
patients with diminished defenses but in 35 % of the cases, no obvious underlying
conditions are found (6). The genus Capnocytophaga belongs to the Family of
Flavobacteriaceae, Class Flavobacteria. Very little is known about Flavobacteria in
general and no genome have been sequenced yet.
In our preliminary investigations, we have developed all the needed genetic tools and
we have generated a library of 7'000 Tn mutants. We are halfway in our effort to
sequence the genome. We have demonstrated that C.canimorsus induces little
inflammatory response and that some strains even block the response to E.coli LPS.
We want to decipher the active and passive mechanisms protecting this bacterium
from the innate immunity. We also want to determine whether, all the strains found in
dog's saliva are of equal danger because this might lead to prevention. This will be
done by comparing the genome sequence (in progress) of a strain isolated from a
fatal human septicaemia to the genome of strains isolated from dogs.
6. Le Moal, G., Landron, C.,Grollier, G., Robert, R. and Burucoa, C. 2003. Clin. Infect Dis 36: 42-6