Characterization of Listeria monocytogenes operon required for stress resistance and virulence

By Xiomarie Alejandro Navarreto

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 regulatory 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 can switch to infect mammalian hosts through the ingestion of contaminated food. PieRS is a two-component signaling system Lm uses to resist ethanol exposure as well as 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. In this dissertation work, we describe studies focused on plasmid insertion inactivation of the PieRS-regulated genes lmo1505/1506, lmo0442, and lmo0881, indicating specific roles for each regulon in resistance to stress conditions. Furthermore, we describe studies focused on in-frame deletion mutants of these regulon members to define individual gene contributions to stress conditions relevant for Lm colonization of the gastrointestinal tract or 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 may play a role in resistance to ethanol stress, a condition that could be relevant to GI colonization as well as in stress resistance associated with food industry production. A closer look at the PieRS regulon Lmo0881 confirms that this protein is secreted into the supernatant of Lm cultures and could be functional as a multimer. All the data present in this dissertation moves our knowledge on the field one step forward regarding how the two-component signaling system in Lm works together with multiple gene products to give an advantage to Lm to survive stress conditions and promote successful infection to the host.