Réponse des lactocoques aux endommagements de la paroi

Le peptidoglycane (PG) est le composant essentiel et majoritaire de l'enveloppe bactérienne. Sa fonction principale est de préserver l'intégrité de la cellule contre la pression osmotique interne. L'apparition des coupures du PG par des autolysines fait partie du processus normal de la croissance de la bactérie, du renouvellement de la paroi cellulaire, de la séparation des cellules, de la germination des spores, de l'autolyse et de la formation des biofilms. Dans la présente étude concernant la réponse des lactocoques à l'activité des hydrolases du PG dans leur paroi, nous avons montré que la résistance à l'hydrolyse par le lysozyme de la bactérie à Gram positif, non pathogène Lactococcus lactis dépend du degré d'acétylation du PG effectué par la surexpression de la déacétylase, PgdA, ou de l'O-acétylase, OatA. Également, nous avons identifié le gène spxB comme un possible régulateur positif d'oatA, et nous avons démontré que son expression est sous le contrôle du système régulateur à deux composants CesSR, lequel répond au stress subit par l'enveloppe cellulaire. Dans notre travail nous avons montré que les gènes qui participent à la réponse au stress de l'enveloppe cellulaire sont également responsables, non seulement de la résistance au lysozyme, mais aussi de la résistance aux antibiotiques aminoglycosidiques et à la vancomycine.The peptidoglycane (PG) is the essential component of the bacterial cell wall. Its principal function is to preserve the integrity of the cell from internai osmotic pression. The introduction of breaks by PG 1 hydrolases is part of normal bacterial cell wall growth, processus and is involved in spore germination, autolysis and biofilm formation. ln the present study of response to cell wall damage by PG hydrolysis, we show that resistance to lysozyme of Gram positive non pathogen bacteria Lactococcus lactis depends on the degree deacetylation of PG : the overexpression of PG déacétylase PgdA or O-acétylase OatA both conferred resistance to the hydrolysis. Also we identified the gene spxB as a possible positive regulator of oatA, and showed that its expression is under the control of the two components system CesSR, which responds to cell wall stress. We showed that genes which take part in the response to the cell wall stress are responsible not only for lactococcal resistance to the lysozyme but also for resistance to aminoglycosidic antibiotics and the vancomycine.COMPIEGNE-BU (601592101) / SudocSudocFranceF

SpxB Regulates O-Acetylation-dependent Resistance of Lactococcus lactis Peptidoglycan to Hydrolysis

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SpxB Regulates O-Acetylation-dependent Resistance of Lactococcus lactis Peptidoglycan to Hydrolysis

Endogenous peptidoglycan (PG)-hydrolyzing enzymes, the autolysins, are needed to relax the rigid PG sacculus to allow bacterial cell growth and separation. PGs of pathogens and commensal bacteria may also be degraded by hydrolases of animal origin (lysozymes), which act as antimicrobials. The genetic mechanisms regulating PG resistance to hydrolytic degradation were dissected in the Gram-positive bacterium Lactococcus lactis. We found that the ability of L. lactis to counteract PG hydrolysis depends on the degree of acetylation. Overexpression of PG O-acetylase (encoded by oatA) led to bacterial growth arrest, indicating the potential lethality of oatA and a need for its tight regulation. A novel regulatory factor, SpxB (previously denoted as YneH), exerted a positive effect on oatA expression. Our results indicate that SpxB binding to RNA polymerase constitutes a previously missing link in the multistep response to cell envelope stress, provoked by PG hydrolysis with lysozyme. We suggest that the two-component system CesSR responds to this stress by inducing SpxB, thus favoring its interactions with RNA polymerase. Induction of PGO-acetylation by this cascade renders it resistant to hydrolysis.