Engineers find a way to protect microbes from extreme conditions

Microbes used for health, agriculture or other applications must be able to withstand the extreme conditions and ideally the manufacturing processes used to make tablets for long-term storage. MIT researchers have now developed a new way to make microbes strong enough to withstand these extreme conditions.

Their method involves mixing the bacteria with food and drug additives from a list of ingredients that the FDA classifies as “generally regarded as safe.” The researchers identified formulations that help stabilize several different types of microbes, including yeast and bacteria, and they showed that these formulations can withstand high temperatures, radiation and industrial processing that can damage vulnerable microbes.

In an even more extreme test, some of the microbes recently returned from a trip to the International Space Station, coordinated by Houston Science and Research Manager Phyllis Friello, and researchers are now analyzing how well the microbes did in able to afford them. the conditions.

“What this project was about was stabilizing organisms for extreme conditions. We’re really thinking about a wide range of applications, be it space missions, human applications or agricultural uses,” says Giovanni Traverso, a professor of associate professor of mechanical engineering at MIT, a gastroenterologist at Brigham and Women’s Hospital and lead author of the study.

Miguel Jimenez, a former research scientist at MIT who is now an assistant professor of biomedical engineering at Boston University, is the lead author of the paper, which appears in Materials of Nature.

To survive in extreme conditions

About six years ago, Traverso’s lab began working on new approaches to make beneficial bacteria like probiotics and microbial therapies more resilient. As a starting point, the researchers analyzed 13 commercially available probiotics and found that six of these products did not contain as many live bacteria as indicated on the label.

“What we found was that—perhaps not surprisingly—there is a difference, and it can be significant,” says Traverso. “So the next question was, given that, what can we do to help the situation?”

For their experiments, the researchers chose four different microbes to focus on: three bacteria and one yeast. These microbes are Escherichia coli Nissle 1917, a probiotic; Ensifer meliloti, a bacterium that can fix nitrogen in the soil to support plant growth; Lactobacillus plantarum, a bacterium used to ferment food products; and the yeast Saccharomyces boulardii, which is also used as a probiotic.

When microbes are used for medical or agricultural applications, they are usually dried into a powder through a process called lyophilization. However, they cannot normally be made into more useful forms such as tablets or pills because this process requires exposure to an organic solvent, which can be toxic to bacteria. The MIT team tried to find additives that could improve the microbes’ ability to survive this type of processing.

“We developed a workflow where we can take materials from the FDA’s ‘generally regarded as safe’ list of materials, and mix and match them with bacteria and ask, are there ingredients that increase the viability of the bacteria in the process of lyophilization?” says Traverso.

Their setup allows them to mix the microbes with one of about 100 different ingredients and then grow them to see which ones survive best when stored at room temperature for 30 days. These experiments revealed different compounds, mainly sugars and peptides, that worked best for each type of microbe.

The researchers then selected one of the microbes, E. coli Nissle 1917, for further optimization. This probiotic has been used to treat “traveler’s diarrhea,” a condition caused by drinking water contaminated with harmful bacteria. The researchers found that if they combined caffeine or yeast extract with a sugar called melibiose, they could create a highly stable formulation of E. coli Nissle 1917.

This mixture, which the researchers called formulation D, allowed survival rates greater than 10% after the microbes were stored for six months at 37 degrees Celsius, while a commercially available formulation of E. coli Nissle 1917 lost all viability after only 11 days below those. the conditions.

Formulation D was also able to withstand much higher levels of ionizing radiation, up to 1000 grays. (The typical radiation dose on Earth is about 15 micrograys per day, and in space, it is about 200 micrograys per day.)

The researchers don’t know exactly how their formulations protect the bacteria, but they hypothesize that the additives may help stabilize bacterial cell membranes during rehydration.

Stress tests

The researchers then showed that these microbes can not only survive the harsh conditions, but also maintain their function after these exposures. After Ensifer meliloti was exposed to temperatures of up to 50 degrees Celsius, the researchers found that they were still able to form symbiotic nodules in plant roots and convert nitrogen into ammonia.

They also found that their formulation of E. coli Nissle 1917 was able to inhibit the growth of Shigella flexneri, one of the leading causes of diarrhea-related deaths in low- and middle-income countries, when the microbes were grown together in a laboratory. dish.

Last year, several strains of these extremophile microbes were sent to the International Space Station, which Jimenez describes as “the ultimate stress test.”

“Even just transport on Earth to pre-flight validation and storage to flight are part of this test, with no temperature control en route,” he says.

The samples were recently returned to Earth, and Jimenez’s lab is now analyzing them. He plans to compare samples that were kept inside the ISS with others that were attached to the outside of the station, as well as control samples that remained on Earth.

Other authors of the paper include Johanna L’Heureux, Emily Kolaya, Gary Liu, Kyle Martin, Husna Ellis, Alfred Dao, Margaret Yang, Zachary Villaverde, Afeefah Khazi-Syed, Qinhao Cao, Niora Fabian, Joshua Jenkins, Nina Fitzgerald, Karavasili , Benjamin Muller and James Byrne.

This story is reprinted courtesy of MIT News (web.mit.edu/newsoffice/), a popular site covering news about research, innovation, and teaching at MIT.