pH range

Edge evidence

• external pH defines bounded pH growth window METPO:2007500

  External pH defines the axis over which the growth window is bounded.

  • DOI:10.1038/nrmicro2549 external pH Supports external pH as the axis bounding the growth window.
• acid tolerance defines bounded pH growth window METPO:2007500

  Acid tolerance sets the lower bound of the pH growth window.

  • DOI:10.1016/j.tim.2007.02.005 highly impermeable cell membranes Supports envelope proton barriers as the lower-bound mechanism for low-pH growth.
• alkaline tolerance defines bounded pH growth window METPO:2007500

  Alkaline tolerance sets the upper bound of the pH growth window.

  • DOI:10.1038/nrmicro2549 alkaliphiles Supports alkaline-tolerance physiology as the upper-bound mechanism for high-pH growth.
• bounded pH growth window manifests as pH range METPO:2007400

  The bounded pH growth window manifests the pH-range phenotype.

  • DOI:10.1038/nrmicro2549 pH homeostasis Supports the trait endpoint.
• transmembrane pH gradient (ΔpH) contributes to bounded pH growth window RO:0002326

  The transmembrane pH gradient sets whether cytoplasmic pH can be maintained across the external pH range.

  • DOI:10.1038/nrmicro2549 PMF architecture (Δψ − 59 ΔpH) determines the range of pHout over which bacteria can tolerate or grow.
• membrane potential (Δψ) compensates for external pH

  Adjustment or reversal of the membrane-potential PMF component offsets extreme external pH stress.

  • DOI:10.1038/nrmicro2549 Under strong pH stress the orientation of a PMF component can reverse to maintain homeostasis.
• cytoplasmic pH homeostasis enables bounded pH growth window RO:0002327

  Keeping cytoplasmic pH compatible with protein function enables growth across the external pH range.

  • DOI:10.1038/nrmicro2549 Bacteria maintain a distinct cytoplasmic pH required for protein function, bounding the phenotype.
• membrane proton impermeability extends acid tolerance

  Reduced proton leak helps maintain cytoplasmic pH and extends growth to lower external pH.

  • DOI:10.3389/fmicb.2020.556140 Modification of membrane lipid composition to reduce proton permeability is a general acid-stress mechanism.
• Mrp Na+/H+ antiporter activity supports alkaline tolerance

  Na+/H+ exchange imports protons and is a principal strategy for alkaline pH homeostasis.

  • DOI:10.1038/nrmicro2549 Na+/H+ antiport is the principal strategy for cytoplasmic pH homeostasis at high external pH.
• amino-acid decarboxylation alkalinizes cytoplasmic pH homeostasis

  Glutamate or arginine decarboxylation consumes intracellular protons, supporting cytoplasmic pH at acidic external pH.

  • DOI:10.3389/fmicb.2020.556140 Decarboxylation of glutamate or arginine is a recurring proton-consuming acid-response module.