Genetics of enveloppe cell factors linked with immobilized bacterial growth

    Activiteit: Examination, teaching and supervision external institutionAcademic


    We studied two cell wall polymers implicated in biofilm formation: exopolysaccharide (EPS) and peptidoglycan (PG). Our investigation of capsule exopolysaccharides (CPS) of Streptococcus pneumoniae revealed that (i) CPS- mutants emerge from immobilized colonies in semi-liquid medium, (ii) a phase variation mecanism may be implied in appearance of mutations in tts gene, responsible for CPS synthesis, (iii) immobilisation is the factor providing a selective pressure. Since PG integrity affects biofilm formation, we looked for new molecular factors affecting PG synthesis or degradation. One of these factors, identified by subtractive genome analysis, is the gene aslA, responsible for D-Asp incorporation in the PG. Its conditional inactivation allowed us to confirm its function as D-Asp ligase and to show that it is indispensable. We also identified genes which could regulate lytic activity of PG hydrolysis and in thus affect PG integrity. We found three genes, overexpression if which leads to more resistant to hydrolysis PG: pgdA , oatA and spxB, encoding respectively for a PG de-acetylase, a PG O-acetylase, and the positive regulator of oatA. Our results allowed us to reveal the multi-step cascade of regulatory mechanisms, provoked by cell wall stress. It starts with induction of two component system CesSR in response to cell wall stress, and ends up with O-acetylation of PG by OatA as a mean of rendering it more resistant to hydrolytic damage. SpxB appeared to be a missing link between response to cell envelope stress and PG modification.
    GeëxamineerdePatrick Veiga
    Examen gehouden op
    • Universite Paris-Sud XI, UFR Scientifique D’Osay
    Mate van erkenningInternational