Yeast fermentations — Certain Candida production strains require plastic-lined fermenters because they are extremely sensitive to trace contamination of which metal?

Introduction / Context:
High-performance yeast fermentations (e.g., single-cell protein or specialty bioconversions by Candida spp.) often demand tight control of trace metals. Even microgram-per-liter contamination from vessel walls can inhibit growth or alter product profiles.

Given Data / Assumptions:

• Some Candida strains have stringent metal tolerance ranges.
• Stainless steel can leach iron and other metals under acidic/aerated conditions.
• Plastic-lined equipment minimizes leaching.

Concept / Approach:
Among common trace metals, iron is both essential and potentially inhibitory when present as uncontrolled contaminants. Many Candida industrial strains have well-documented sensitivity to iron carryover; plastic linings (or glass/epoxy coatings) are used to prevent trace iron pickup that can depress growth or shift metabolism.

Step-by-Step Solution:

Verification / Alternative check:
Operational guidelines for sensitive yeasts recommend inert linings or non-metallic contact surfaces specifically to prevent iron exposure.

Why Other Options Are Wrong:

• Cobalt/Nickel: may affect enzymes at high levels, but the classic lining rationale points to iron leaching.
• None: contradicts the stated need for plastic lining.

Common Pitfalls:
Assuming all stainless steels are chemically inert; under process conditions, trace Fe can dissolve and impact delicate yeasts.

Final Answer:
traces of iron