obligately acidophilic

Edge evidence

• acidic external pH selects for obligately acidophilic METPO:2007401

  Acidic environments select for organisms with acidic pH growth optima.

  • DOI:10.3389/fmicb.2021.822229 acidic optimal growth pH Review supports acidophile classification by acidic optimum pH; the obligate neutral-pH exclusion remains from the METPO definition.
• acidic external pH increases gradient of proton METPO:2007601

  Low external pH creates a steep proton gradient across the membrane.

  • DOI:10.3389/fmicb.2021.822229 proton gradient across the cytoplasmic membrane Supports external-to-internal proton gradient under low-pH growth.
• low proton permeability membrane limits influx of proton

  Reduced membrane permeability helps obligate acidophiles maintain intracellular pH.

  • DOI:10.1016/j.tim.2007.02.005 highly impermeable cell membranes Supports proton exclusion by membrane properties in acidophiles.
• reversed membrane potential suppresses influx of proton

  Reversed membrane potential reduces passive proton entry.

  • DOI:10.1016/j.tim.2007.02.005 reversed membrane potential Supports reversed membrane potential as a shared acidophile feature.
• proton export pumps and antiporters contributes to cytoplasmic pH homeostasis RO:0002326

  Proton export and antiport systems contribute to intracellular pH control during acid stress.

  • DOI:10.3389/fmicb.2021.822229 proton export pumps and antiporters Supports transporter-mediated acid resistance mechanisms.
• cytoplasmic pH homeostasis enables obligately acidophilic RO:0002327

  Obligate acidophilic growth requires maintaining cytoplasmic pH despite acidic external pH.

  • DOI:10.1038/nrmicro2549 maintain a cytoplasmic pH of approximately 6.0 Supports intracellular pH control during extreme acidophilic growth.
• K+ uptake system (Kdp/Kef) increases reversed membrane potential RO:0002213

  K+ uptake systems generate the inside-positive (reversed) membrane potential that forms an electrochemical barrier to protons.

  • DOI:10.3389/fmicb.2023.1149903 Review describes inside-positive membrane potential via potassium-transporting ATPases and K+ uptake systems (kdp, Kef) forming an electrochemical barrier to proton influx.
• P-type proton-translocating ATPase increases proton efflux from cytoplasm RO:0002213

  P-type ATPases actively export protons from the cytoplasm.

  • DOI:10.3389/fmicb.2023.1149903 Dopson review lists active proton efflux via P-type ATPases as a pH homeostasis strategy in acidophiles.
• proton efflux from cytoplasm contributes to cytoplasmic pH homeostasis RO:0002326

  Active proton efflux helps maintain near-neutral cytoplasmic pH under acidic conditions.

  • DOI:10.3389/fmicb.2023.1149903 Proton pumps/ATPases maintain a near-neutral cytoplasm during acidophilic growth.
• Na+/H+ antiporter (Nha) exports proton METPO:2000209

  Na+/H+ antiporters exchange cytoplasmic protons for extracellular sodium, contributing to proton export.

  • DOI:10.3389/fmicb.2023.1149903 Dopson lists Na+/H+ exchange (nhaA sodium/proton antiporter) among acidophile pH-homeostasis systems.
• hopanoid-containing membrane decreases low proton permeability membrane RO:0002212

  Hopanoid membrane lipids reduce membrane proton permeability, reinforcing proton exclusion.

  • DOI:10.1111/1758-2229.70019 Acid resistance is linked to hopanoid membrane lipids and reduced proton permeability as a core proton-exclusion strategy.
• cyclopropane fatty acids decreases low proton permeability membrane RO:0002212

  Cyclopropane fatty acid formation reduces membrane proton permeability.

  • DOI:10.3389/fmicb.2023.1149903 Review includes cyclopropane-fatty-acyl-phospholipid synthase among membrane adaptations that reduce proton permeability.
• glutamate decarboxylase system (Gad) consumes proton biolink:consumes

  Glutamate decarboxylase consumes cytoplasmic protons during decarboxylation, buffering intracellular pH.

  • DOI:10.3389/fmicb.2023.1149903 Review lists decarboxylases (Adi, Gad) as cytoplasmic proton-consuming systems used in acidophile pH homeostasis.