Winning abstract!

Contributions of the two-component signaling system PieRS and its associated regulon
to Listeria monocytogenes gastrointestinal colonization

Xiomarie Alejandro-Navarreto, and Nancy E. Freitag

Environmental microbes must often cope with variations encountered in physicochemical
conditions, including temperature, UV light exposure, nutrient availability, oxygen tension, and
osmolarity. One mechanism used by bacteria to respond to environmental changes relies on cell
signaling mediated by two-component signaling systems (TCSs), which are able to translate rapid
environmental changes into regulatory readouts. Listeria monocytogenes (Lm) is a gram-positive
foodborne pathogen that is ubiquitous in the environment and that can infect mammalian hosts
following the ingestion of contaminated food. PieRS is a two-component signaling system that Lm
uses to resist ethanol exposure as well as to regulate the chaperones PrsA1, PrsA2, and the
serine protease chaperone HtrA. PieRS regulates the expression of additional gene products that
have not been described but may be associated with roles in stress conditions and virulence.
Here we describe studies focused on in-frame deletion mutants of the PieRS-regulated genes
lmo1505, lmo0442, and lmo0881 in order to define their individual gene contributions to stress
conditions relevant for Lm colonization of the gastrointestinal tract and within the environment.
Analysis of an intragastric mouse model of infection suggests that Lmo0442 and Lmo0881 have
roles in promoting bacteria colonization of the gastrointestinal tract during Lm infection.
Additionally, Lmo0442 was shown to have a role in adhesion during the infection of colonic
epithelial cell lines. In the case of Lmo1505, experimental data suggested it plays a role in
resistance to ethanol stress, a condition that could be relevant for GI colonization as well as in
stress resistance associated with the food industry production. Preliminary characterization of the
PieRS regulon member Lmo0881 indicates that is secreted into the supernatant of Lm cultures
and that it may be functional as a multimer. Understanding the role and contributions of PieRS
regulon members provides additional insight into how Lm adapts to a variety of environmental
stressors that include the challenging environment of the mammalian gastrointestinal system