Microbial producers for L-lysine (direct method): Which organism/strain type is classically employed for the commercial “direct fermentation” of L-lysine?

Introduction / Context:
L-lysine production is a hallmark of industrial microbiology. It relies on aerobic, high-cell-density fermentation with robust producers from the coryneform group. Historically, nomenclature has changed (e.g., Micrococcus glutamicus is an older name; Corynebacterium glutamicum is widely used now), but the concept of using improved (mutated/selected) strains remains central.

Given Data / Assumptions:

• “Direct method” refers to single-organism microbial fermentation from sugars to L-lysine.
• Industrial processes typically deploy improved or mutated strains to remove feedback inhibition and increase flux toward lysine biosynthesis.
• Legacy organism names appear in classic exam options.

Concept / Approach:
Among traditional exam answers, the mutated strain of Micrococcus glutamicus (now recognized as Corynebacterium glutamicum) is most closely associated with commercial lysine production by direct fermentation. While other coryneform bacteria (e.g., Brevibacterium spp.) are also used, the best single match to the phrasing “direct method” in classic references is the improved strain of Micrococcus/Corynebacterium.

Step-by-Step Solution:
Map “direct fermentation” to coryneform bacteria used at scale.Recognize naming conventions: Micrococcus glutamicus ≈ Corynebacterium glutamicum in older literature.Choose the option specifying an improved/mutated strain to reflect industrial practice.

Verification / Alternative check:
Process patents and textbooks consistently cite improved coryneform strains (e.g., auxotrophs or deregulated mutants) for high-yield L-lysine production.

Why Other Options Are Wrong:
Wild-type strains (without improvement) are typically insufficient for industrial titers. Other species listed have been explored, but the most classical answer for direct L-lysine fermentation is the mutated Micrococcus/Corynebacterium lineage.

Common Pitfalls:
Overlooking historical names or assuming only one genus is ever used; multiple genera exist, but exam conventions favor the coryneform prototype.

Final Answer:
Mutated strain of Micrococcus glutamicus