The green transformation of the L-isoleucine fermentation process

The green transformation of L-isoleucine fermentation processes mainly focuses on strain breeding, fermentation condition optimization, resource recycling, etc., with specific progress as follows:

High-Yield Strain Breeding

Genetic engineering technologies are used to modify production strains, improving L-isoleucine yield and sugar-acid conversion rate while reducing by-product formation. For example, replacing the ilva promoter of Corynebacterium glutamicum with the tac promoter, knocking out related genes followed by complementation and overexpression of specific genes, constructs auxotrophic strains that enhance acid production without antibiotic addition. Additionally, combining high-throughput screening with traditional mutagenesis helps isolate high-yield mutants with unknown traits.

Fermentation Condition Optimization

Dissolved Oxygen Control

Oxygen supply is critical in L-isoleucine fermentation. Studies show that using Brevibacterium lactofermentum as the production strain, maintaining dissolved oxygen at 20% via dissolved oxygen feedback control maximizes acid production and productivity. A two-stage oxygen control mode (e.g., stirring at 700 r/min for 0–10 h and 600 r/min for 10–56 h) also improves acid yield.

Osmotic Pressure Regulation

Controlling osmotic pressure with ammonium sulfate dilutions not only provides inorganic nitrogen for fermentation but also regulates key enzyme activities, increasing L-isoleucine yield and reducing organic acid synthesis. Stage-controlled fermentation broth osmotic pressure can significantly boost L-isoleucine production to 6.2% and reduce miscellaneous acid content to 0.15%.

Resource Recycling

Treating amino acid fermentation wastewater is a key part of green transformation. Existing patented technologies include:

Adsorbing and precipitating fermentation supernatant with montmorillonite powder, where the supernatant is used for irrigation and the precipitate mixed with cells as fertilizer.

Separating supernatant from glutamic acid fermentation, recovering ammonium sulfate as chemical fertilizer, and using the un-recovered solid part—after phosphoric acid hydrolysis—as fermentation ingredients, achieving resource recycling.

Exploration of Novel Fermentation Methods

Research has attempted L-isoleucine fermentation using autotrophic microorganisms. Taking C. necator, which can utilize CO₂ as the sole carbon source for autotrophic growth, as the starting strain, genetic engineering was used to construct an L-isoleucine biosynthesis pathway based on pyruvate and acetyl-CoA. This first achieved CO₂-based L-isoleucine production in autotrophic fermentation, offering a new direction for green L-isoleucine fermentation processes.