Lecture Notes: pH Tolerance in Organisms

Optimal pH Range for Growth

• Most organisms:
  • Grow best between pH 6 to pH 8.
  • Internal pH must remain near-neutral for cellular macromolecule functionality, particularly proteins.

Internal vs. External pH

• Internal pH:
  • Remains neutral regardless of highly acidic or basic external environments.

Categories of Organisms by pH Preference

Neutrophiles

• Description:
  • Prefer circum-neutral pH (5.5 to 7.9).
  • Known as neutral-loving organisms.
• Example:
  • E. coli.

Acidophiles

• Description:
  • Thrive in low pH environments (acidic).
  • Commonly found in acidic soils, e.g., volcanic activity areas.
• Adaptation:
  • Stabilize their cytoplasmic membranes using high concentrations of protons (H+).
  • Utilize protons for membrane stability.

Alkaliphiles

• Description:
  • Grow best at high pH values (alkaline).
  • Found in soda lakes and high carbonate soils.
• Adaptation:
  • May use sodium ions instead of protons for creating energy gradients.
  • Struggle with membrane bioenergetics and producing a proton-motive force.