Select the typical operating pH range for chlorotetracycline fermentation in industrial practice:

Introduction / Context:
Chlortetracycline (Aureomycin) is produced by Streptomyces species with process control over pH, temperature, aeration, and feeds. pH affects enzyme activity, antibiotic stability, and morphology, so a proper range is essential for good titers.

Given Data / Assumptions:

• Industrial-scale submerged fermentation.
• Use of complex nitrogen/CSL and buffering (often CaCO3).
• Desire to balance growth and production with minimal degradation.

Concept / Approach:
For many tetracycline fermentations, near-neutral pH conditions are favored. Too acidic (below ~6) can hinder growth and enzyme function; too alkaline (above ~7.5–8) risks instability and undesirable by-products. Hence, pH 6–7 is a widely cited working band for production stability and yield.

Step-by-Step Solution:

Verification / Alternative check:
Multiple process descriptions report initial pH near neutrality and control trajectories maintained in the 6–7 range for best titers and reduced degradation.

Why Other Options Are Wrong:

• pH 5–6: often suboptimal for production.
• pH 7–8 or 8–9: tends toward instability/degradation or morphology issues.

Common Pitfalls:
Confusing growth-optimum pH with product-stability optimum; tetracyclines can degrade more quickly at higher pH.

Final Answer:
pH 6–7