Acid Survival Mechanisms in Neutralophilic Bacteria

Abstract

Numerous commensal and pathogenic Gram-negative and Gram-positive bacteria are referred to as neutralophiles because they grow best at pH levels close to neutrality. Thus, exposure to harsh-to-mild acidic environments, such as those encountered in the digestive tract of animal hosts, in the phagosome of macrophages, in fermented foods, but also in the soil or in acid mine drainage, is a rather common encounter for neutralophiles during their life cycle. As a result, it is not surprising that most of them have evolved sophisticated molecular mechanisms to cope with low pH. These protective mechanisms provide neutralophiles with the ability to sense acid pH and keep under control the intracellular acidification of the cytoplasm, thus avoiding protons from reaching such harmful levels as to compromise cellular vitality, which relies on the proper functioning of many biological macromolecules at pH levels near neutrality.\ud \ud The aim of this chapter is to provide an overview of the most commonly employed, and best characterized, molecular systems in a number of Gram-positive and Gram-negative bacteria. How they work inside the cell and how their activity can be linked to virulence are highlighted. The biochemistry and distribution of the glutamate-dependent acid resistance system among orally acquired bacteria are described in some detail

The proton motive force determinesEscherichia coli’s robustness to extracellular pH

“…S10) and should be positive for sufficiently acidic pH e . This prediction is consistent with observations that cells responds to acidic stress by directly or indirectly generating positive charge: some amino acids to are converted into more positively charged molecules and negatively charged glutamate is converted into neutral γ -aminobutyric acid [58, 59, 60].…”

Probing the viability of palladium‐challenged bacterial cells using flow cytometry

“…Moreover, other work using acid‐tolerant bacteria (background described in Eguchi and Utsumi and in Pennacchietti et al . ) showed that the Pd(0) deposition and catalytic activity of the resulting ‘bio‐Pd(0)’ was indistinguishable in parental and acid‐resistant cells of E. coli (L. Zajac, A.J. Murray, P.A.…”

Exploitation of microbial activities at low pH to enhance planetary health

“…A paradigmatic case of both the negative and positive impacts that the metabolic changes induced by acid stress responses may have on human health outcomes is exemplified by the various amino acid decarboxylases that are induced by cell exposure to acid pH. Decarboxylation pathways are activated in acid conditions as they catalyze the conversion of an amino acid into a biogenic amine, generating carbon dioxide and consuming a proton, thus contributing to the maintenance of the intracellular pH and improved survival at low pH (Pennacchietti et al 2016 , Lund et al 2020 ). On the negative side, some biogenic amines produced by micro-organisms through the action of decarboxylases, such as histamine (from His), tyramine (from Tyr), 2-phenylethylamine (from Phe), tryptamine (from Trp), putrescine (from ornithine or through the agmatine deiminase pathway, which follows the decarboxylation of arginine to agmatine), and cadaverine (from Lys), can cause several adverse reactions to consumers, such as tingling tongue, rash, vomiting, diarrhea, burning sensation, headache and dizziness, nausea, palpitations, or breathing difficulties.…”