Global Transcriptional Response of Three Highly Acid-Tolerant Field Strains of Listeria monocytogenes to HCl Stress

Abstract

Tolerance to acid is of dual importance for the food-borne pathogen Listeria monocytogenes: acids are used as a preservative, and gastric acid is one of the first defenses within the host. There are considerable differences in the acid tolerance of strains. Here we present the transcriptomic response of acid-tolerant field strains of L. monocytogenes to HCl at pH 3.0. RNAseq revealed significant differential expression of genes involved in phosphotransferase systems, oxidative phosphorylation, cell morphology, motility, and biofilm formation. Genes in the acetoin biosynthesis pathway were upregulated, suggesting that L. monocytogenes shifts to metabolizing pyruvate to acetoin under organic acid stress. We also identified the formation of cell aggregates in microcolonies as a potential relief strategy. A motif search within the first 150 bp upstream of differentially expressed genes identified a novel potential regulatory sequence that may have a function in the regulation of virulence gene expression. Our data support a model where an excess of intracellular H+ ions is counteracted by pumping H+ out of the cytosol via cytochrome C under reduced activity of the ATP synthase. The observed morphological changes suggest that acid stress may cause cells to aggregate in biofilm microcolonies to create a more favorable microenvironment. Additionally, HCl stress in the host stomach may serve as (i) a signal to downregulate highly immunogenic flagella, and (ii) as an indicator for the imminent contact with host cells which triggers early stage virulence genes.

Time-course Transcriptome of Parageobacillus thermoglucosidasius DSM 6285 Grown in the Presence of Carbon Monoxide and Air

“…In E. coli, phosphotransacetylase Pta and the acetate kinase AckA have been shown to reversibly convert acetate to acetyl CoA [32,41]. This is also consistent with the observed up-regulation of the transcripts qoxA, qoxC and qoxA, which are upregulated in L. monocytogenes in response to acid stress [42]. However, two transcripts, atpD and atpC, coding for the β and ε subunits of the F 1 F 0 -type ATP synthetase are significantly up-regulated at the 44h timepoint relative to the aerobic (8h) timepoint.…”

Transcriptome Sequencing of Listeria monocytogenes Reveals Major Gene Expression Changes in Response to Lactic Acid Stress Exposure but a Less Pronounced Response to Oxidative Stress

“…Multiple studies have demonstrated that lmo2230 is a member of the σ B regulon (Raengpradub et al, 2008;Oliver et al, 2009;Toledo-Arana et al, 2009;Utratna et al, 2011). These studies also showed that lmo2230 is upregulated during early stationary phase (Raengpradub et al, 2008;Oliver et al, 2009), within the murine intestinal lumen (Toledo-Arana et al, 2009) and in response to osmotic and acid stress (Raengpradub et al, 2008;Utratna et al, 2011;Horlbog et al, 2019). Heat and cold stress have also been shown to induce lmo2230 expression (van der Veen et al, 2007;Hingston et al, 2017a), and lmo2230 is also upregulated after chlorine dioxide exposure (Pleitner et al, 2014).…”

“…In addition to differences in experimental conditions, the differences in upregulation of lmo2230 could be explained by different timepoints, different L. monocytogenes strains, and/or the usage of a microarray compared to RNA sequencing. Although upregulation of lmo2230 in response to stress has been observed in numerous studies (van der Veen et al, 2007;Raengpradub et al, 2008;Oliver et al, 2009;Toledo-Arana et al, 2009;Utratna et al, 2011;Pleitner et al, 2014;Hingston et al, 2017a;Horlbog et al, 2019), its function in L. monocytogenes remains uncharacterized. The weak amino acid identity of Lmo2230 to the arsenate reductase ArsC from B. subtilis might suggest a possible role in heavy metal detoxification.…”

Pathogenicity and virulence of Listeria monocytogenes: A trip from environmental to medical microbiology

“…However, these stress responses entail an extensive cell reprogramming with pleiotropic effects, which are still poorly understood. For example, recent transcriptomic analyses involving distinct L. monocytogenes strains subjected to acidic conditions (pH = 3.0) showed enhanced expression of genes belonging to both GAD and ADI systems, along with hundreds of differentially expressed genes with no obvious involvement in acid tolerance [ 141 , 142 ]. This is also true of other stress responses, such as those triggered by low temperature [ 101 ], high osmolality [ 143 ], QACs [ 144 ], or bile salts [ 140 ].…”