Streptococcus agalactiae est la première cause d’infections néonatales, et est aussi un pathogène émergent chez l’adulte immunodéprimé. L’objectif de ce travail de thèse a été de caractériser l’opéron métabolique fru2 de S. agalactiae (i) en étudiant sa phylogénie, (ii) en identifiant ses inducteurs, et (iii) en élaborant son schéma de régulation. Cet opéron est composé de 7 gènes qui codent un activateur transcriptionnel de la famille DeoR-like (Fru2R), un transporteur PTS (PTSFru2), et trois enzymes qui sont potentiellement impliquées dans la voie non oxydative des pentoses phosphates. Nous avons mis en évidence que cet opéron avait été acquis au cours de l’évolution, et n’était présent que chez les souches de complexes clonaux responsables d’infections chez l’adulte immunodéprimé et la personne âgée. Nous avons ensuite montré que certains milieux complexes, sources de carbone, et liquides biologiques humains permettaient l’activation de cet opéron. Ensuite, nous avons caractérisé le rôle et fonctionnement de la protéine Fru2R (i) en montrant son rôle d’activateur transcriptionnel, (ii) en identifiant les acides aminés essentiels à son activité, et (iii) en démontrant sa capacité à se fixer au niveau de la région promotrice de fru2. / Streptococcus agalactiae, commonly known as group B streptococcus, is a leading cause of neonatal morbidity and mortality. It is also an emergent pathogen in immunocompromised and elderly adults. The objective of this study was to characterize the phylogeny, the induction and the regulation of the S. agalactiae fru2 operon. This operon encodes a PTS transporter of the fructose-mannitol family, a transcriptional activator of the DeoR-like family, an allulose-6 phosphate-3-epimerase, a transaldolase and a transketolase. Our results, concerning the phylogeny, indicate that fru2 was acquired during the evolution of S. agalactiae. Then, we highlighted that the fru2 promoter was active in complex medium, in chemically defined medium with various carbon sources and in human biological fluids. Then, we demonstrated that the Fru2R protein (i) was a transcriptional activator, (ii) contains amino acids which are essential for the activity of the Fru2R and fru2 promoter, and (iii) interacts with the fru2 intergenic region. Then, we demonstrated the role of the PTSFru2 proteins of S. agalactiae A909 fru2.

This thesis applies the ab initio techniques of computational chemistry to studies of molecular clusters containing covalent (strong) or van der Waals (weak) bonds formed in chemistry and biochemistry in the temperature range 10-300 K. Van derWaals complexes with an enthalpy of formation from reactants of less than 25 kJ mol-1 and covalent clusters are described in this thesis. The first group of van der Waals complexes involved the molecule carbon monoxide that possesses a small permanent dipole that could lead to dipole - induced dipole interaction and dipole - dipole interaction with another reactant in addition to dispersion. The substrates investigated were methanimine and cyanogen where endergonic unstable molecules were formed, and the clustering of carbon monoxideon a porphin surface leading to the formation of carbon - carbon fragments. TheFaraday effect was invoked to suggest that this was the original method by which thechirality of the D-sugars was selected. Coordination of imino-compounds on thesame surface involving induction and electrostatic interactions could lead to the preferential formation of L-aziridones, hydrolysable to L-amino-acids.The preferred formation of D-ribose, and the more stable D-2-deoxyribose, andnucleotides polymerisable to deoxyribonucleic acids was described. The second group of van der Waals complexes involved the polymerisation of acetylene molecules, to di- and tri-acetylene complexes where the exchange interaction involved the quadrupole moment of the acetylene radical reacting with acetylene or diacetylene. The reaction of carbon monoxide was extended to include its interaction with diacetylene. The entire potential energy surface for the interaction with diacetylene was investigated. The reaction was shown to be endergonic to produce a reactive species, here postulated to rearrange with a reasonable activation energy toform an aldehyde. The energetics of the formation of diacetylene, triacetylene andhigher polymers was briefly investigated. The reactivity of the acetylene polymeraldehydes with other substrates was briefly investigated. This work has apparently laid a firm basis both, qualitative and quantitative, tounderstand some of the weakest interactions in nature involving the simplest ofreactions that have been important in atmospheric chemistry.