A milestone in amino-acid biotechnology: The first large-scale commercial process used to produce L-lysine by microorganisms is commonly referred to as which type of fermentation process?

Introduction / Context:
L-lysine is an essential amino acid widely produced for feed supplementation and food applications. Early commercial biotechnological routes shifted from chemical synthesis to microbial production using selected and improved strains. This question targets the terminology used to describe that pioneering large-scale bioprocess.

Given Data / Assumptions:

• The focus is on the first commercial microbial process for L-lysine.
• Industrial practice adopted specific labels for routes that used one organism in a single step versus more complex or staged approaches.
• Terminology distinguishes “direct” microbial fermentation from chemical or multistep hybrid routes.

Concept / Approach:
“Direct fermentation” describes the microbial conversion of carbohydrate feedstocks into L-lysine in a single bioreactor pathway using improved bacteria (for example, coryneform bacteria). This contrasts with terms like “dual” or “indirect,” which imply multi-stage, coupled, or non-purely microbial routes. Historically, direct fermentation became the foundation for the modern L-lysine industry.

Step-by-Step Solution:
Recall industrial shift: chemical → microbial for cost and sustainability.Associate first commercial success with one-step microbial bioprocess.Identify this route’s canonical name as “direct fermentation.”

Verification / Alternative check:
Process descriptions from the amino-acid industry document direct fermentation using carbohydrate substrates, aerated tanks, and strain improvement to maximize yields.

Why Other Options Are Wrong:
“Dual” or “indirect” fermentation do not denote the historically accepted one-step microbial route and are not standard names for the original process. A combined answer cannot be correct because only one term is historically canonical.

Common Pitfalls:
Confusing generic “multi-step processing” with named fermentation categories; assuming the earliest processes were hybrid when, in fact, direct fermentation soon dominated.

Final Answer:
direct fermentation