Transcriptome signatures of class I and III stress response deregulation in Lactobacillus plantarum reveal pleiotropic adaptation

Hermien Van Bokhorst-Van De Veen,Peter A Bron,Roger S Bongers,Michiel Kleerebezem,Michiel Wels

doi:10.1186/1475-2859-12-112

Abstract

BackgroundTo cope with environmental challenges bacteria possess sophisticated defense mechanisms that involve stress-induced adaptive responses. The canonical stress regulators CtsR and HrcA play a central role in the adaptations to a plethora of stresses in a variety of organisms. Here, we determined the CtsR and HrcA regulons of the lactic acid bacterium Lactobacillus plantarum WCFS1 grown under reference (28°C) and elevated (40°C) temperatures, using ctsR, hrcA, and ctsR-hrcA deletion mutants.ResultsWhile the maximum specific growth rates of the mutants and the parental strain were similar at both temperatures (0.33 ± 0.02 h-1 and 0.34 ± 0.03 h-1, respectively), DNA microarray analyses revealed that the CtsR or HrcA deficient strains displayed altered transcription patterns of genes encoding functions involved in transport and binding of sugars and other compounds, primary metabolism, transcription regulation, capsular polysaccharide biosynthesis, as well as fatty acid metabolism. These transcriptional signatures enabled the refinement of the gene repertoire that is directly or indirectly controlled by CtsR and HrcA of L. plantarum. Deletion of both regulators, elicited transcriptional changes of a large variety of additional genes in a temperature-dependent manner, including genes encoding functions involved in cell-envelope remodeling. Moreover, phenotypic assays revealed that both transcription regulators contribute to regulation of resistance to hydrogen peroxide stress. The integration of these results allowed the reconstruction of CtsR and HrcA regulatory networks in L. plantarum, highlighting the significant intertwinement of class I and III stress regulons.ConclusionsTaken together, our results enabled the refinement of the CtsR and HrcA regulatory networks in L. plantarum, illustrating the complex nature of adaptive stress responses in this bacterium.

Highlights

To cope with environmental challenges bacteria possess sophisticated defense mechanisms that involve stress-induced adaptive responses
HrcA and CtsR are involved in the heat stress response of L. plantarum HrcA and CtsR are regulators of class I and class III stress responses, respectively, including heat induced stress [13]
The role of these repressors at reference and elevated temperature was investigated in L. plantarum and its previously constructed derivatives that are deficient in either CtsR or HrcA alone, or both [38]

Summary

Introduction

To cope with environmental challenges bacteria possess sophisticated defense mechanisms that involve stress-induced adaptive responses. Many stress conditions induce protein denaturation and aggregation, and bacteria, including lactobacilli, possess conserved chaperones and proteases to restore or remove misfolded or denatured proteins. This process has extensively been studied in the paradigm Gram-positive bacterium Bacillus subtilis using abruptly or constantly elevated temperatures as the inducing stress condition. CtsR binds to a heptanucleotide repeat (A/GGTCAAA/T), referred to as the CtsR box [20] This cis-acting regulatory element is commonly encountered in the promoter regions of clpP and several other, but not all, clp genes, which encode Clpproteases that are involved in protein quality control during both stress and non-stress conditions [21]. HrcA and CtsR are key components in stress response regulation, which may include cross-regulation between their respective regulons

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