Comparative Review of the Responses of Listeria monocytogenes and Escherichia coli to Low pH Stress

Abstract

Acidity is one of the principal physicochemical factors that influence the behavior of microorganisms in any environment, and their response to it often determines their ability to grow and survive. Preventing the growth and survival of pathogenic bacteria or, conversely, promoting the growth of bacteria that are useful (in biotechnology and food production, for example), might be improved considerably by a deeper understanding of the protective responses that these microorganisms deploy in the face of acid stress. In this review, we survey the molecular mechanisms used by two unrelated bacterial species in their response to low pH stress. We chose to focus on two well-studied bacteria, Escherichia coli (phylum Proteobacteria) and Listeria monocytogenes (phylum Firmicutes), that have both evolved to be able to survive in the mammalian gastrointestinal tract. We review the mechanisms that these species use to maintain a functional intracellular pH as well as the protective mechanisms that they deploy to prevent acid damage to macromolecules in the cells. We discuss the mechanisms used to sense acid in the environment and the regulatory processes that are activated when acid is encountered. We also highlight the specific challenges presented by organic acids. Common themes emerge from this comparison as well as unique strategies that each species uses to cope with acid stress. We highlight some of the important research questions that still need to be addressed in this fascinating field.

Listeria monocytogenes Requires the RsbX Protein To Prevent SigB Activation under Nonstressed Conditions

“…The challenges presented by the host during infection can be overcome by L. monocytogenes using a variety of adaptive mechanisms ( 2 , 5 ). For instance, the bacterium can utilize glutamate decarboxylation and arginine deamination to control its cytoplasmic pH, use bile salt hydrolase and drug efflux pumps to protect against bile stress, and use solute transport systems for osmoregulation when facing osmotic stress ( 3 , 6 ). It can also deploy a well-coordinated repertoire of virulence factors ( 2 ).…”

Host - Bacterial Pathogen Communication: The Wily Role of the Multidrug Efflux Pumps of the MFS Family

“…As shown in Figure 3 , mdtEF is co-transcribed with gadE as a gadE-mdtEF operon. EvgS/EvgA is one of the many systems that control the expression of this operon ( Arcari et al, 2020 ) ( Figure 3 ). It is assumed that the environment inside macrophages is acidic and oxidative, hosts toxic molecules such as antimicrobial peptides, causes genotoxic stress, and lacks important nutrients ( Demarre et al, 2019 ).…”

Acid stress signals are integrated into the σB-dependent general stress response pathway via the stressosome in the food-borne pathogen Listeria monocytogenes

“…Following the entry into the host, L. monocytogenes can withstand an array of potentially lethal conditions in the GI tract, such as the extreme acid pH of the stomach, high osmotic pressure and high concentration of bile salts in the duodenum (reviewed in [5,6]. L. monocytogenes employs the alternative sigma factor B (σ B ) to upregulate a regulon of approximately 300 genes, which collectively confer an array of homeostatic and protective mechanisms that allow survival under severe stress conditions (reviewed in [7,8]. L. monocytogenes relies on σ B to enhance survival in the GI tract and to establish infection [9].…”

“…L . monocytogenes employs the alternative sigma factor B (σ B ) to upregulate a regulon of approximately 300 genes, which collectively confer an array of homeostatic and protective mechanisms that allow survival under severe stress conditions (reviewed in [ 7 , 8 ]. L .…”