The food-borne
pathogen Listeria monocytogenes is adapted to a diversity of environments, such as soil, food,
body fluids, and the
cytosol of eukaryotic cells. The transition between
saprophytic and
pathogenic life is mediated through complex regulatory pathways that modulate the expression of
virulence factors. Here we examined the expression of inlJ, a recently identified gene encoding a protein of the LPXTG-internalin family and involved in
pathogenesis. We show that inlJ expression is controlled neither by the major listerial regulator of
virulence genes, PrfA, nor by AxyR, a putative
AraC regulator encoded by a gene adjacent to inlJ and divergently transcribed. The InlJ protein is not produced by
bacteria grown in vitro in
brain heart infusion medium or replicating in the
cytosol of tissue-cultured cells. In contrast, it is efficiently produced and localized at the surface of
bacteria present in the
liver and
blood of infected animals. Strikingly, the expression of inlJ by a
heterologous promoter in
L. monocytogenes or L. innocua promotes
bacterial adherence to
human cells in vitro. Taken together, these results strongly suggest that InlJ acts as a novel
L. monocytogenes sortase-anchored
adhesin specifically expressed during
infection in vivo.
