The role of the alternative s 54 factor, encoded by the rpoN gene, was investigated in Listeria monocytogenes by comparing the global gene expression of the wild-type EGDe strain and an rpoN mutant. Gene expression, using whole-genome macroarrays, and protein content, using two-dimensional gel electrophoresis, were analysed. Seventy-seven genes and nine proteins, whose expression was modulated in the rpoN mutant as compared to the wild-type strain, were identified. Most of the modifications were related to carbohydrate metabolism and in particular to pyruvate metabolism. However, under the conditions studied, only the mptACD operon was shown to be directly controlled by s 54. Therefore, the remaining modifications seem to be due to indirect effects. In parallel, an in silico analysis suggests that s 54 may directly control the expression of four different phosphotransferase system (PTS) operons, including mptACD. PTS activity is known to have a direct effect on the pyruvate pool and on catabolite regulation. These results suggest that s 54 is mainly involved in the control of carbohydrate metabolism in L. monocytogenes via direct regulation of PTS activity, alteration of the pyruvate pool and modulation of carbon catabolite regulation.

Listeria monocytogenes is the causative agent of listeriosis, one of the most significant foodborne diseases in industrialized countries. The complete genome of the L. monocytogenes EGDe strain, belonging to the serogroup 1/2a, has been sequenced and is comprised of 2853 open reading frames. The objective of the current study was to construct a two-dimensional (2-D) database of the proteome of this strain. The soluble protein fractions of the microorganism were recovered either in the mid-log or in the stationary phase of growth at 37 degrees C. These fractions were analyzed by 2-D electrophoresis (2-DE), using immobilized pH gradient strips of various pH values (3-10, 3-6, and 5-8) for the first-dimensional separations and 12.5% acrylamide gels for sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). 201 protein spots corresponding to 126 different proteins were identified by matrix assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS). The 2-DE maps presented here provide a first basis for further investigations of protein expression in L. monocytogenes. In this way, the comparison of proteome between cells in the exponential or stationary phase of growth at 37 degrees C allowed us to characterize 161 variations in protein spot intensity, of which 38 were identified. Among the differentially expressed proteins were ribosomal proteins (RpsF, RplJ, and RpmE), proteins involved in cellular metabolism (GlpD, PdhD, Pgm, Lmo1372, Lmo2696, and Lmo2743) or in stress adaptation (GroES and ferritin), a fructose-specific phosphotransferase enzyme IIB (Lmo0399) and different post-translational modified forms of listeriolysin (LLO).

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In the laboratories, the studies on bacteria are generally carry out from planktonic cells, growing in a liquid medium. However, in the natural environments, more than 90% of the micro-organisms have a sessile mode of growth, adhered to a biotic or an abiotic surface. They can then form biofilms which correspond to microbial aggregates surrounded by a matrix of exopolymers. Under this mode of growth, it is known that the micro-organisms are more resistant to environmental variations and stresses, to cleaning disinfection treatments or to antibiotics.Listeria monocytogenes is an ubiquitous Gram-positive rod that can be found in the ground, the hydraulic networks or on vegetables as well as in the food industry environments. This bacterium can also be present in the gastrointestinal tract of animals and humans as asymptomatic carriage strain. This germ is the causative agent of the listeriosis, a foodborne disease which can be very serious for high-risk groups such as old persons, pregnant women, neonates, immunocompromised adults. Although the frequency of listeriosis outbreaks decreased thanks to the efforts of the food industry working people and to the implementation of efficient system of control, the sanitary risk remains important. So, during year 1999, two hundred seventy cases were registered in France (1) with a mortality rate of 23%. For the food industry, the economic consequences linked to a foodborne listeriosis outbreak are dramatic because, besides the direct loss due to the withdrawal and the destruction of the incriminated product, the indirect losses due to the deterioration of the brand image of the product can be fatal to the company.In pure culture, L. monocytogenes is able to form biofilms on numerous abiotic surfaces such as stainless steel, glass or polytetrafluoroethylene (PTFE or teflon) (2-6). In the plants of foodstuff production and transformation, L. monocytogenes can be isolated within pluri-microbial biofilms formed on the surfaces of equipments. So, it represents a potential source of contamination of food products.