Genomic and proteomic analysis of the Alkali-Tolerance Response (AlTR) in Listeria monocytogenes 10403S

Abstract

Background: Information regarding the Alkali-Tolerance Response (AlTR) in Listeria monocytogenes is very limited. Treatment of alkali-adapted cells with the protein synthesis inhibitor chloramphenicol has revealed that the AlTR is at least partially protein-dependent. In order to gain a more comprehensive perspective on the physiology and regulation of the AlTR, we compared differential gene expression and protein content of cells adapted at pH 9.5 and un-adapted cells (pH 7.0) using complementary DNA (cDNA) microarray and two-dimensional (2D) gel electrophoresis, (combined with mass spectrometry) respectively.

Results: In this study, L. monocytogenes was shown to exhibit a significant AlTR following a 1-h exposure to mild alkali (pH 9.5), which is capable of protecting cells from subsequent lethal alkali stress (pH 12.0). Adaptive intracellular gene expression involved genes that are associated with virulence, the general stress response, cell division, and changes in cell wall structure and included many genes with unknown functions. The observed variability between results of cDNA arrays and 2D gel electrophoresis may be accounted for by posttranslational modifications. Interestingly, several alkali induced genes/proteins can provide a cross protective overlap to other types of stresses.

Conclusion: Alkali pH provides therefore L. monocytogenes with nonspecific multiple-stress resistance that may be vital for survival in the human gastrointestinal tract as well as within food processing systems where alkali conditions prevail. This study showed strong evidence that the AlTR in L. monocytogenes functions as to minimize excess alkalisation and energy expenditures while mobilizing available carbon sources.

Figure 1

Survival of L. monocytogenes mean populations in BHI (30°C) adjusted to pH 12.0 for 120 min. Populations were either adapted at pH 9.5 with the presence of chloramphenicol (▲) or without chloramphenicol (▼) and not adapted at pH 9.5 (Control cultures) (■). Error bars indicate s.e.m.

Figure 2

Comparisons of 2D electrophoresis gels of proteins extracted from control (A) and adapted (B) cultures. The reference numbers correspond to those listed in Additional file 1.