Transcriptome Sequencing Reveals Distinct Stress Response of <i>Listeria monocytogenes</i> 6179 During Logarithmic and Stationary Growth Phases

Listeria monocytogenes is a food-borne pathogen that continues to threaten food safety by persisting in food production environments (FPEs). Its tolerance to stressors introduced in FPEs is well characterized; however, the effect of the growth phase on stress response gene expression is less understood. Here, we utilize transcriptome sequencing to analyze gene expression of the persistent L. monocytogenes strain 6179 in response to 30-min exposure to either lactic acid or oxidative stress when grown to either logarithmic or stationary growth phase. Analysis of this data revealed distinct gene expression responses to stress exposure between the two growth phases. Exposure to lactic acid (1%, pH 3.4) resulted in 1809 significant (Q < 0.05, log₂fold changes with absolute values ≥ 1) differentially expressed (DE) genes in stationary phase cells and 175 significant DE genes in logarithmic growth phase cells. Upon oxidative stress exposure (15 mM hydrogen peroxide), 184 significant DE genes were observed in the stationary phase and 819 significant DE genes in the logarithmic phase. Interestingly, in the logarithmic growth phase, 37 of the 50 most upregulated genes were shared between responses to acid and oxidative stress; these included genes involved in cysteine transport. In contrast, stationary phase cell gene expression was more influenced by the type of stress exposure, and the majority of upregulated genes were members of the σ^B regulon. Collectively, these results provide further insight into the impact of growth phase on gene expression in L. monocytogenes in response to lactic acid and hydrogen peroxide stress exposure.