Industrial riboflavin (vitamin B2) biosynthesis: Which Ascomycete fungi are classically used for large-scale riboflavin production?

Introduction / Context:
Riboflavin is an essential vitamin used as a supplement and colorant. Fungal bioprocesses using certain Ascomycetes have long produced riboflavin efficiently via overproduction pathways.

Given Data / Assumptions:

• Candidates include Eremothecium (Eremnothecium) ashbyii and Ashbya gossypii, well-known riboflavin overproducers.
• We must determine which are employed industrially.

Concept / Approach:
Ashbya gossypii (teleomorph of Eremothecium) and Eremothecium ashbyii are classic riboflavin producers, selected for deregulated pathways (GTP and ribulose-5-phosphate flux) and strong secretion. Although yeasts can produce B-vitamins, Candida species listed are not the principal industrial riboflavin organisms.

Step-by-Step Solution:
Recognize historical strain usage: A. gossypii and E. ashbyii. Note their taxonomic relationship and overproduction traits. Choose the combined option.

Verification / Alternative check:
Process literature and patents repeatedly cite these Ascomycetes for vitamin B2 manufacture.

Why Other Options Are Wrong:

• Single entries (a) or (b) are incomplete.
• Candida guilliermondia: not the standard platform for B2.

Common Pitfalls:
Overlooking teleomorph–anamorph naming and assuming unrelated yeasts are primary producers.

Final Answer:
Both (a) and (b)