Purpose: To examine cold shock gene expression differences associated with fast and slow (cold growth lag phase period <70 h compared to >200 h in BHI at 4°C) cold adaptation phenotypes amongst L. monocytogenes strains.
Methods: Lm 60 and EGD-e, representing fast and slow cold adapting L. monocytogenes strains, respectively, were exposed to cold stress induced by transfer from 37 to 4°C, and their transcription responses were compared at 30, 60, and 120 min of cold acclimation.
Results: Lm 60 up regulated (≥ 2.5-fold) the expression of 200 genes compared to EGD-e. Up regulated genes were associated with carbohydrate and amino acid transport and metabolism, peptidoglycan synthesis, cell surface proteins, general stress responses, transcription regulation, flagella biosynthesis and motility. Comparative phenotypic analysis showed that cold adapted Lm 60 cells to be more tolerant to cell wall and bile stress exposure than EGD-e, as well as displaying enhanced flagellation, swarming motility, biofilm formation and cold growth in defined growth medium using fructose as a carbon source.
Significance: Genome wide insights into genetic response differences between a fast (Lm 60) and a slow (EGD-e) cold adapting L. monocytogenes strain have been provided by the present study. Our observations suggest more proficient cold adaptation in Lm 60 compared to EGD-e might be promoted through enhanced nutrient uptake and metabolism abilities as well as improved stress tolerance under cold stress.