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July 09, 2024

MIT Develops Method to Extend Shelf Life of Beneficial Bacteria

Researchers at the Massachusetts Institute of Technology (MIT) have developed a groundbreaking technique to help beneficial microbes withstand extreme conditions, thereby extending their shelf life in medicines and agricultural products.

The innovative method, spearheaded by Giovanni Traverso, an associate professor of mechanical engineering at MIT, employs a range of food and drug additives to fortify live cultures like yeast and bacteria against high temperatures, radiation, and the harsh conditions of industrial processing. This development was detailed in a recent issue of the journal Nature Communications.

The research team has demonstrated that by mixing these microbes with specific ingredients-primarily sugars and peptides-their survival rate over 180 days improves significantly. This enhancement is evident not only at room temperature but also at elevated temperatures up to 50 degrees Celsius (122 degrees Fahrenheit) and under high radiation exposure.

Currently, the team is evaluating how well a batch of these modified microbes endured the challenging environment of space after a recent return from the International Space Station (ISS).

A Six-Year Journey to Enhance Microbial Stability

This advancement is the result of a six-year research project funded by NASA's Translational Research Institute for Space Health. The goal was to improve the efficacy of bacteria used in probiotics and microbial therapeutics by making them more resilient.

Initial tests on 13 commercially available probiotics revealed that six contained fewer live bacteria than advertised due to the drying process or the use of organic solvents during tablet formation. These methods can be toxic to the bacteria. To address this issue, the researchers sought to identify additives that could boost the microbes' resistance to these processes.

The study focused on several types of microbes:

- Escherichia coli Nissle 1917: A probiotic used to treat "traveler's diarrhea."

- Ensifer meliloti: A bacterium that aids plant growth by fixing nitrogen in the soil.

- Lactobacillus plantarum: A bacterium involved in food fermentation.

- Saccharomyces boulardii: A yeast also used as a probiotic.

Creating Resilient Microbial Formulations

"We developed a workflow where we can take materials from the 'generally regarded as safe' materials list from the FDA, and mix and match those with bacteria and ask, are there ingredients that enhance the stability of the bacteria during the lyophilization process?" Traverso explained.

In their experiments, the researchers discovered that combining caffeine or yeast extract with a sugar called melibiose resulted in a highly stable form of E. coli Nissle 1917, referred to as "formulation D." This new formulation exhibited survival rates of over 10% after six months at 37 degrees Celsius, compared to the commercially available E. coli Nissle 1917, which lost all viability after just 11 days.

Additionally, the modified formulation demonstrated resistance to extremely high levels of ionizing radiation-up to 1,000 grays-far exceeding typical levels found on Earth or even in space. The average daily radiation levels are about 15 micrograys on Earth and 200 micrograys in space.

Practical Applications and Future Research

The fortified microbes retained their intended functions even after exposure to severe conditions. For example:

- Ensifer meliloti was able to form symbiotic nodules on plant roots and convert nitrogen to ammonia at temperatures up to 50 degrees Celsius.

- E. coli Nissle 1917 successfully inhibited the growth of Shigella flexneri in vitro, a major cause of diarrhea-related deaths in lower-income countries.

While the exact mechanism by which these formulations protect the bacteria is not fully understood, researchers hypothesize that the additives may help stabilize the bacteria's cell membranes during rehydration.

Testing in Space

Samples of these robust microbes were sent to the ISS in what Miguel Jimenez, lead author and assistant professor of biomedical engineering at Boston University, described as "the ultimate stress test." Some samples were exposed to the harsh conditions outside the space station, while others were kept inside. These samples have now returned to Earth, and Jimenez's lab is comparing them against control samples that remained on the ground.

Collaborative Efforts and Funding

This research was supported by various institutions, including NASA's Translational Research Institute for Space Health, Space Center Houston, MIT's Department of Mechanical Engineering, the 711th Human Performance Wing, and the Defense Advanced Research Projects Agency (DARPA).

The successful development of this technique marks a significant step forward in extending the shelf life and stability of beneficial microbes, potentially revolutionizing their use in medicine and agriculture. With ongoing analysis and further testing, this approach could pave the way for new applications in harsh environments, from industrial processes to space exploration.