The two-component system PrlS/PrlR of Brucella melitensis is required for persistence in mice and appears to respond to ionic strength Mirabella, Aurélie and Yañez Villanueva, Rosse-Mary and Delrue, Rose-May and Uzureau, Sophie and Zygmunt, Michel S. and Cloeckaert, Axel and De Bolle, Xavier and Letesson, Jean-Jacques,, 158, 2642-2651 (2012), doi = https://doi.org/10.1099/mic.0.060863-0, publicationName = Microbiology Society, issn = 1350-0872, abstract= Bacterial adaptation to environmental conditions is essential to ensure maximal fitness in the face of several stresses. In this context, two-component systems (TCSs) represent a predominant signal transduction mechanism, allowing an appropriate response to be mounted when a stimulus is sensed. As facultative intracellular pathogens, Brucella spp. face various environmental conditions, and an adequate response is required for a successful infection process. Recently, bioinformatic analysis of Brucella genomes predicted a set of 15 bona fide TCS pairs, among which some have been previously investigated. In this report, we characterized a new TCS locus called prlS/R, for probable proline sensor–regulator. It encodes a hybrid histidine kinase (PrlS) with an unusual Na+/solute symporter N-terminal domain and a transcriptional regulator (belonging to the LuxR family) (PrlR). In vitro, Brucella spp. with a functional PrlR/S system form bacterial aggregates, which seems to be an adaptive response to a hypersaline environment, while a prlS/R mutant does not. We identified ionic strength as a possible signal sensed by this TCS. Finally, this work correlates the absence of a functional PrlR/S system with the lack of hypersaline-induced aggregation in particular marine Brucella spp., language=, type=