Remodeling of the Listeria monocytogenes cell wall inside eukaryotic cells

Listeria monocytogenes is an intracellular Gram-positive bacterial pathogen that produces many types of surface proteins. To get insights into its intracellular lifestyle, we used high-resolution mass spectrometry to characterize the cell wall proteome of bacteria proliferating within the eukaryotic cell. The relative amount of a few surface proteins was found notoriously different in intracellular bacteria. Internalin A (InlA), which is covalently bound to the peptidoglycan and plays a central role in bacterial entry into non-phagocytic eukaryotic cells, was present in high amounts in the cell wall of intracellular bacteria. Our study also revealed that the actin assembly-inducing protein ActA co-purified with peptidoglycan isolated from intracellular bacteria. Growth of L. monocytogenes in minimal media reproduced the predominance of InlA in the cell wall and the association of ActA with peptidoglycan. Intriguingly, bacteria grown in this condition used ActA for efficient invasion of host cells. These findings suggest that the adaptation of L. monocytogenes to the intracellular lifestyle involves changes in the relative abundance of certain surface proteins and in their mode of association to the peptidoglycan. These alterations, probably promoted by yet-unknown changes in the cell wall architecture, may instruct these proteins to perform different functions outside and inside the host cell.