The Story of S. cerevisiae TFS9
A tiny organism found in Iranian tea soil might hold the key to a better cup of decaf.
For millions, the day doesn't start until that first cup of coffee. Yet for many others, the jitters, anxiety, or sleeplessness that can follow caffeine consumption is a steep price to pay. Traditional decaffeination processes, often relying on chemical solvents, can strip coffee of its precious flavor alongside its stimulant. But what if nature offered a more delicate solution?
Scientists are now turning to biodecaffeination—using living microorganisms to gently remove caffeine. At the forefront of this research is a remarkable strain of yeast, discovered in the soils of northern Iran's tea plantations: Saccharomyces cerevisiae TFS9. This novel organism not only survives in environments that would be toxic to other yeasts but can actually consume caffeine as its food 1 .
The global demand for decaffeinated coffee is steadily rising, driven by growing health consciousness and the desire for coffee's flavor without its stimulatory effects . However, the conventional methods for decaffeinating coffee have significant drawbacks.
Uses chemicals like methylene chloride or ethyl acetate. While safe in regulated amounts, the process can leave residues and remove flavor compounds non-selectively .
A chemical-free method that, while safer, can still lead to a loss of the sugars and amino acids that contribute to coffee's complex taste profile .
Effective but requires high-pressure equipment, making it a very costly technology .
Leverages biodegradation, where microbes actively break down caffeine molecule by molecule. This offers a potential pathway that is more natural, cost-effective, and less damaging to flavor 1 .
The story of TFS9 begins not in a coffee lab, but in a tea field. Researchers hunting for caffeine-tolerant microorganisms isolated 16 different yeast strains from the cultivated tea soils of northern Iran. The logic was simple: soil surrounding caffeine-producing plants is a likely home for microbes that have evolved to use caffeine as a nutrient 1 .
The researchers used an agar dilution method to screen for the most resilient strain. They grew the isolated yeasts on petri dishes containing increasing concentrations of caffeine. While many strains showed some tolerance, one standout performer emerged—the strain designated TFS9 1 .
Through rigorous analysis of its morphological, biochemical, and genetic characteristics (specifically its ITS1–5.8S–ITS2 rDNA sequences), TFS9 was identified as a unique strain of the common baker's yeast, Saccharomyces cerevisiae. It was deposited in a genetic database under the accession number KF414526 1 . This was a significant finding, as it provided the first evidence that S. cerevisiae, a yeast renowned for its role in baking and brewing, could also be a potent degrader of caffeine 1 .
To confirm TFS9's abilities, scientists designed a crucial experiment to measure its caffeine degradation power in liquid culture 1 .
The TFS9 yeast was inoculated into a minimal salt medium—a simple, nutrient-broken solution where caffeine was provided as the sole source of carbon.
The medium was spiked with a high concentration of caffeine, 3.5 grams per liter (g/L), creating a stressful environment that would inhibit the growth of most ordinary yeasts.
The culture was left to incubate for 60 hours. During this time, researchers regularly sampled the supernatant (the liquid part of the culture after yeast cells are removed).
The caffeine concentration in the supernatant was measured using a UV-visible spectrophotometer, which detects changes in the concentration of a compound by how it absorbs light 1 .
The results were striking. After the 60-hour incubation period, the caffeine concentration in the medium had plummeted from 3.5 g/L to just 0.53 g/L 1 .
| Time Point (Hours) | Caffeine Concentration (g/L) | Percentage Remaining |
|---|---|---|
| 0 | 3.5 | 100% |
| 60 | 0.53 | 15.2% |
| Metric | Result |
|---|---|
| Initial Caffeine Concentration | 3.5 g/L |
| Final Caffeine Concentration | 0.53 g/L |
| Incubation Time | 60 hours |
| Caffeine Degradation Efficiency | 84.8% |
| Need for Process Optimization? | No (without) |
This represents a massive 84.8% reduction in caffeine content. Importantly, this high level of degradation was achieved without any additional optimization of the process, such as tweaking the pH, temperature, or nutrient levels. This suggests that TFS9 is naturally primed for this task, pointing to a highly efficient and simple process for decaffeinating caffeine-containing solutions 1 .
| Research Tool / Reagent | Function in the Experiment |
|---|---|
| Minimal Salt Medium | A simple growth solution with defined salts; forces the yeast to rely solely on caffeine for carbon and energy. |
| Caffeine | The target molecule for degradation; served as the sole carbon source in the medium to apply selective pressure. |
| UV-Visible Spectrophotometer | An analytical instrument that measures the absorption of light by a compound; used to quantify the remaining caffeine. |
| Agar Plates | Solid growth media used for the initial isolation of yeast strains and to screen for caffeine tolerance. |
| Incubator | A temperature-controlled chamber to maintain optimal growth conditions (e.g., 30°C) for the yeast during the experiment. |
For a microbe, high concentrations of caffeine are toxic. It inhibits a crucial cellular signaling regulator called TOR (Target of Rapamycin), which controls growth and metabolism 2 4 7 . So, how does TFS9, and other caffeine-tolerant yeasts, survive and even thrive?
Yeast cells can expel caffeine using specialized transporter proteins that act like molecular pumps in their cell membrane. Key players are the ABC transporters Snq2 and Pdr5 7 . Studies using experimental evolution have shown that when yeast is forced to adapt to high-caffeine environments, it often acquires mutations in genes like PDR1 and PDR5 2 4 . These are typically "gain-of-function" mutations that supercharge the production or efficiency of these pumps, flushing caffeine out of the cell before it can cause harm 2 4 .
Another evolutionary adaptation involves making the cell less sensitive to caffeine's attack. Scientists have found that caffeine-tolerant strains sometimes have "loss-of-function" mutations in genes that are effectors of the TOR pathway, such as SIT4, SKY1, and TIP41 4 . By disrupting these components, the inhibitory signal from caffeine is blunted, allowing the cell's growth and metabolism to continue relatively unimpeded 4 .
While the exact genetic makeup of TFS9 is still being explored, its high tolerance suggests it possesses one or both of these sophisticated biological adaptations.
The implications of TFS9's ability extend beyond a single laboratory experiment. The field of synthetic biology is rapidly developing tools to engineer yeasts like S. cerevisiae for enhanced traits 3 . Techniques like adaptive laboratory evolution (ALE)—where yeasts are gradually exposed to higher caffeine levels to force adaptation—and more direct CRISPR-Cas9 gene editing could be used to create even more robust and efficient decaffeination strains 2 3 .
Apply this biodecaffeination process directly during coffee fermentation. Instead of removing caffeine with chemicals after the beans are processed, selected or engineered microbes like TFS9 could be added during the wet fermentation stage, naturally reducing caffeine content while potentially even enhancing flavor complexity through their metabolic activity .
Saccharomyces cerevisiae TFS9 is more than a scientific curiosity; it is a beacon of a more natural and precise approach to creating the foods and beverages we enjoy. Its discovery in tea soil reminds us that solutions to modern challenges are often hidden in plain sight, within the intricate workings of the natural world. As research progresses, the day may come when your perfectly balanced, flavorful, and naturally decaffeinated cup of coffee is courtesy of a microscopic ally—a humble yeast with a taste for caffeine.
This article is based on scientific findings published in peer-reviewed journals, including Progress in Biological Sciences.