Researchers Engineered a Cheese Starter Bacteria to Boost GABA and Eliminate a Toxic Byproduct

Cheese already does a lot of things well, but a team of researchers wanted to make it do one more: deliver meaningful amounts of gamma-aminobutyric acid, or GABA, without carrying along a toxic hitchhiker called putrescine. In a study published in the Journal of Dairy Science, Sampedro et al. report that a precisely engineered strain of Lactococcus lactis can produce GABA-enriched Cabrales-like mini-cheeses containing 545 to 865 mg of GABA per kilogram, with no detectable putrescine accumulation. The work is preliminary, but it resolves what had been the central obstacle to using this bacterial strain safely in commercial dairy production.

Why GABA in food is worth engineering toward

GABA is the brain's primary inhibitory neurotransmitter, but its potential reach extends well beyond neurons. Research compiled in a comprehensive review of GABA's pharmaceutical properties credits the compound with antihypertensive, anxiolytic, anti-diabetic, and antioxidant activities, among others. That broad profile has made GABA a target for functional food developers, and fermented dairy products are a natural fit: they already involve lactic acid bacteria that can convert glutamate into GABA through enzymatic activity. Consumer demand for foods with documented physiological effects is pushing investment in this space, and the global GABA market is projected to reach approximately USD 143.3 million by 2033, with microbial fermentation identified as the most scalable production route.

The putrescine problem in Lactococcus lactis

L. lactis is the workhorse of the dairy fermentation industry. Its generally recognized as safe (GRAS) status, compact and fully sequenced genome, and well-developed genetic tools have made it a model organism for engineering food-grade bacteria. The problem is that certain wild-type L. lactis strains carry the AGDI cluster, a set of genes responsible for converting agmatine into putrescine. Putrescine is a biogenic amine, and its presence in aged cheeses is not merely a regulatory nuisance. Research on biogenic amines in fermented foods shows that putrescine can amplify the toxicity of histamine and react with nitrite to form carcinogenic nitrosamines. It also contributes unpleasant flavors and aromas. A strain that produces GABA but also accumulates putrescine offers a poor trade-off for any food producer aiming at a health-forward product.

Deleting the AGDI cluster via double homologous recombination

The researchers addressed this directly by knocking out the AGDI cluster in a GABA-producing L. lactis strain. The method they used, double homologous recombination, is a well-established technique for making precise, scarless deletions in bacterial chromosomes. When the knockout strain was cultivated in a medium supplemented with agmatine, the substrate that wild-type cells convert to putrescine, the mutant produced no detectable putrescine. Critically, the deletion did not interfere with the strain's separate GABA-synthesizing machinery: when glutamate was supplied, the knockout still converted it to GABA at levels comparable to the parent strain. The two biosynthetic pathways operate independently, which meant that silencing one did not compromise the other.

GABA concentrations in experimental mini-cheeses

To test whether the engineered strain would perform under realistic dairy conditions, the team used it as a starter culture for Cabrales-like mini-cheeses. Cabrales is a Spanish blue cheese with a complex ripening process, and the mini-cheese format allowed controlled comparisons. The results were clear: cheeses made with the knockout strain accumulated GABA at concentrations ranging from 545.50 to 865.86 mg per kilogram. Putrescine was undetectable throughout. Those GABA concentrations are substantially higher than what occurs naturally in conventional cheese, and the absence of putrescine removes both the food-safety concern and the sensory defects, such as off-odors, that the wild-type strain would have introduced during ripening. No adverse effects on the basic fermentation process were reported.

Open questions before any commercial application

This is early-stage research, and several things remain unknown. The study used mini-cheeses under laboratory conditions; full-scale production involves different temperature gradients, microbial consortia, and aging durations that could shift both GABA yield and flavor profiles. The specific GABA concentrations required to produce measurable physiological effects in humans who consume cheese are also not established here; the study demonstrates production feasibility, not clinical outcome. Regulatory approval for a genetically modified starter culture in food production varies by jurisdiction and represents its own timeline. The GABA-enriched food sector faces known challenges around strain-dependent variability, storage stability, and compliance frameworks, all of which will apply to any scaled version of this work.

What the research opens up for functional dairy

Despite those caveats, the study addresses a real and previously blocking problem. The AGDI cluster deletion strategy is transferable: the same double homologous recombination approach could in principle be applied to other L. lactis strains used in different cheese styles. GABA-enriched yogurt and other fermented dairy formats are already under active development, and a clean, putrescine-free starter culture with reliable GABA output would be a practical asset for producers in that space. The combination of elevated GABA, no toxic biogenic amine accumulation, and an unchanged fermentation profile positions this engineered strain as a credible candidate for further pilot-scale and regulatory evaluation, assuming the production numbers hold outside the laboratory.

Evidence rating

INVESTIGATIONAL — 61/100

Caveats:

• This is early-stage food engineering research — no human trials have been conducted.
• GABA consumed in food does not reliably cross the blood-brain barrier, so neuroactive effects in humans remain unproven.
• Results come from lab-scale mini-cheeses; performance in commercial production is untested.
• Funding was not disclosed by the authors.

Proof-of-concept laboratory study using a genetically engineered bacterial strain and small-scale cheese models, with no human subjects or clinical endpoints. The work demonstrates GABA production and putrescine elimination at bench scale but cannot establish effects in humans. No independent replication has been reported.

References

1. Lorena Sampedro, Corina Bauer, Begoña Redruello, Miguel A. Alvarez, Beatriz del Rio (2026). Engineering a Lactococcus lactis strain to produce gamma-aminobutyric-acid-enriched, putrescine-free cheese. Journal of Dairy Science. https://doi.org/10.3168/jds.2026-28720
2. Dai-Hung Ngo, Thanh Sang Vo (2019). An Updated Review on Pharmaceutical Properties of Gamma-Aminobutyric Acid. Molecules. https://doi.org/10.3390/molecules24152678
3. Fabian Hernandez-Tenorio, Mateo Mejía-Rúa, Luz Deisy Marín-Palacio, Bernadette Klotz-Ceberio, David Orrego, Catalina Giraldo-Estrada (2025). Advances in Biotechnological GABA Production: Exploring Microbial Diversity, Novel Food Substrates, and Emerging Market Opportunities. International Journal of Molecular Sciences. https://doi.org/10.3390/ijms27010306
4. Adelene Ai-Lian Song, Lionel L. A. In, Swee Hua Erin Lim, Raha Abdul Rahim (2017). A review on Lactococcus lactis: from food to factory. Microbial Cell Factories. https://doi.org/10.1186/s12934-017-0669-x
5. Biogenic amines in foods – PMC. NIH. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6572173/
6. Muhammad Ameer Ushidee-Radzi, Chong Shin Yee, Raja Balqis Raja-Razali, et al. (2025). Advances in GABA-Enriched Yogurt and Frozen Yogurt: Microbial Biosynthesis, Functional Properties, and Health Perspectives—A Comprehensive Review. Foods. https://doi.org/10.3390/foods14244254