Abstract
The ability of Listeria monocytogenes to adapt to various food and food- processing environments has been attributed to its robustness, persistence and prevalence in the food supply chain. To improve the present understanding of molecular mechanisms involved in hyperosmotic and low-temperature stress adaptation of L. monocytogenes, we undertook transcriptomics analysis on three strains adapted to sub-lethal levels of these stress stimuli and assessed functional gene response. Adaptation to hyperosmotic and cold-temperature stress has revealed many parallels in terms of gene expression profiles in strains possessing different levels of stress tolerance. Gene sets associated with ribosomes and translation, transcription, cell division as well as fatty acid biosynthesis and peptide transport showed activation in cells adapted to either cold or hyperosmotic stress. Repression of genes associated with carbohydrate metabolism and transport as well as flagella was evident in stressed cells, likely linked to activation of CodY regulon and consequential cellular energy conservation.
Highlights
The opportunistic food-borne pathogen Listeria monocytogenes is adapted to life in the soil and life inside eukaryotic host cells
We show that L. monocytogenes tolerance and subsequent response to environmental stress is highly strain specific, though the physiological adjustments made are broadly similar between strains as well as between stress conditions
Strain specific tolerance to various stresses has previously been noted in Listeria monocytogenes [3,28,29,30,31], where certain strains appear to be more or less adapted to specific stress
Summary
The opportunistic food-borne pathogen Listeria monocytogenes is adapted to life in the soil and life inside eukaryotic host cells. During its saprophytic life this bacterium can acquire tolerance to a vast array of physical and physiochemical stresses necessary to persist in the environment Such stresses include elevated osmolarity (as high as 14%) [1,2,3] and cold temperature (a slow as -0.1°C) [4]. Broad stress adaptation response in strains of L. monocytogenes possessing different tolerances to hyperosmotic and cold stress conditions was elucidated by cultivation and gene expression-based approaches. Salt stress tolerance experiments L. monocytogenes strains were routinely cultivated on Brain. Cold (4°C) growth experiments L. monocytogenes strains were routinely cultivated on BHIA at 25°C for 24 h. The three strains were grown in 50 mL BHIB under three different sets of conditions: unstressed, salt stressed and cold temperature stressed (4±1°C). Diameter of zones of motility, observed as red swarming halos were measured in millimetres at the widest point with 1mm being an absolute minimum (size of the original stab), indicating zero swarming motility
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