Changes in gene expression during adaptation of Listeria monocytogenes to the soil environment

Abstract

Listeria monocytogenes is a ubiquitous opportunistic pathogen responsible for listeriosis. In order to study the processes underlying its ability to adapt to the soil environment, whole-genome arrays were used to analyse transcriptome modifications 15 minutes, 30 minutes and 18 h after inoculation of L. monocytogenes EGD-e in soil extracts. Growth was observed within the first day of incubation and large numbers were still detected in soil extract and soil microcosms one year after the start of the experiment. Major transcriptional reprofiling was observed. Nutrient acquisition mechanisms (phosphoenolpyruvate-dependent phosphotransferase systems and ABC transporters) and enzymes involved in catabolism of specific carbohydrates (β-glucosidases; chitinases) were prevalent. This is consistent with the overrepresentation of the CodY regulon that suggests that in a nutrient depleted environment, L. monocytogenes recruits its extensive repertoire of transporters to acquire a range of substrates for energy production.

Figure 1. Growth and survival of L. monocytogenes EGD-e in soil microcosms (plain lines) and soil extracts (dashed lines) at 25°C.

(A) Focus on the first two days of incubation. (B) one year incubation. Δ: control soil (TA); □: compost-amended soil (DA).

Figure 2. Venn diagramm of L. monocytogenes EGD-e genes with higher (A) and lower (B) transcript levels during 18 h incubation in soil extract.

Figure 3. qRT-PCR quantification of selected genes with higher and lower transcript levels identified by microarray.

Figure 4. Functional categories identified after gene ontology among genes with higher (A) and lower (B) transcript levels.

Figure 5. Expression levels of the 94 genes with higher transcript levels during incubation in the soil environment (TA).

Each raw of coloured boxes represents one gene. Columns indicate sampling times (0, 15 min, 30 min and 18 h).