Bacterial physiology: For most non-extremophilic bacteria, the optimum pH for growth lies in which range?

Introduction / Context:
Most bacteria commonly encountered in laboratory and clinical settings are neutrophiles, preferring near-neutral pH for optimal enzyme activity and membrane function. Understanding pH preferences helps in designing culture media and controlling microbial growth in industry and healthcare.

Given Data / Assumptions:

• Neutrophiles favor pH close to neutrality.
• Enzyme activity and transport processes drop outside optimal pH.
• Acidophiles and alkaliphiles are special cases, not “most bacteria.”

Concept / Approach:
The majority of laboratory bacteria grow best between pH 6.5 and 7.5. Media such as nutrient broth and tryptic soy broth are buffered around neutrality to sustain growth. Deviations require specialized buffers and adaptations (e.g., for acidophiles like Acidithiobacillus or alkaliphiles like Bacillus alcalophilus).

Step-by-Step Solution:
Classify bacteria: neutrophiles vs acidophiles vs alkaliphiles.Recall the standard neutral range for neutrophiles: ~6.5–7.5.Select “6.5–7.5” as the correct optimum range for most bacteria.

Verification / Alternative check:
Growth curves for common strains (E. coli, Staphylococcus aureus) peak near neutral pH, validating the stated range.

Why Other Options Are Wrong:

• 3.5–6.5 ranges: too acidic for most non-specialized bacteria.
• 8.5–9.5: alkaline range typical of alkaliphiles, not most species.

Common Pitfalls:
Assuming a single pH suits all species; ignoring buffer capacity and CO2 effects in incubators.

Final Answer:
6.5–7.5.