Microorganisms in Microgravity: Spaceflight Experiments Reveal New Properties of Pathogens

Feb 28, 2013 | Steven Purcell | Research & Policy

The International Space Station (ISS), orbiting some 220 miles above earth at a speed of 17,000 miles per hour, is a modern marvel and the pride of national space agencies around the world. With the first pieces launched in 1998, assembly continued until 2011 when the ISS was completed. Today, the ISS with its expansive solar panels is about the size of an American football field, including the end zones. The ISS weighs over 861,804 pounds and has habitable space roughly equivalent to a five bedroom home with two bathrooms. Indeed, the ISS has been continually occupied since the year 2000.

The ISS may seem an improbable platform to carry out infectious disease research, but that’s precisely how microbiologist Cheryl Nickerson of the Biodesign Institute at Arizona State University intends to unlock the secrets of disease-causing microorganisms such as the bacteria salmonella. Scientific experiments on the ISS are commonplace, even with living organisms. However, recent discoveries about the properties of salmonella in space may open the door for some exciting questions and further research regarding common illnesses here on earth.

"One important focus of my research is to use the microgravity [extremely small gravitational force] environment of spaceflight as an innovative biomedical research platform. We seek to unveil novel cellular and molecular mechanisms related to infectious disease progression that cannot be observed here on Earth, and to translate our findings to novel strategies for treatment and prevention", says Nickerson.

While carrying out a number of NASA space shuttle and ground-based experiments, Nickerson and her team learned some intriguing new information regarding the way salmonella bacteria function without the force of gravity influencing the ‘behavior’ of this microorganism. NASA postulates that space travel can ‘trick’ salmonella into behaving as if it were in the human gut (gastrointestinal tract). This is thought to occur as a result of a change in cellular mechanics responding to the surrounding environment, which has changed due to the lack of gravity. As a result, newly observed alterations in the way salmonella functions have shown it to be more virulent in space travel. In other words, the disease-causing capacity of salmonella was amplified in space. The manor in which salmonella was altered is a key interest in the way the bacteria functions on earth.

An established phenomenon known as ‘fluid shear’ may be the explanation for how salmonella bacteria are able to act in space similar to how they act while infecting a human host. Fluid shear refers to the ability of microorganisms to sense the intensity of the flow of liquid in the surrounding environment. For example, salmonella in the stomach can sense when fluid is moving quickly. This environment is not conducive to the bacteria’s proliferation, so it makes its way into the human gut. Here, it can sense that liquid flow is greatly diminished. As a result, salmonella can and will more easily multiply, and the infected individual will soon exhibit symptoms. 

"Cells are funny things," Nickerson says. "If you give them too much or too little of something they're used to having around, they'll surprise you with how they respond."

Simply put, fluid shear affects the functioning of cellular mechanics. Depending on the environment, the flow of fluids around a cell can affect gene regulation. Though research is still ongoing, it is thought that when fluid shear influences genes to switch on or off within a cell (up or down regulation), the flow of ions in and out of a cell is modified, possibly influencing the virulence of the microorganism. By further understanding how these cellular mechanics are modified in space travel, researchers may be able to target or exploit this change in functioning to treat or prevent the spread of disease in astronauts and here on earth. The prospect of ongoing research is exciting, and the implications could be great.

Julie Robinson, program scientist for the International Space Station at NASA’s Johnson Space Center in Houston: “This research opens up new areas for investigations that may improve food treatment, develop new therapies and vaccines to combat food poisoning in humans here on Earth, and protect astronauts on orbit from infectious disease.”

Looking ahead, Nickerson and her colleagues hope to continue exploring pathogenic microorganism behavior in spaceflight and terrestrial scenarios. Recently, Nickerson’s team conducted an experiment during space shuttle mission STS-135 in which a Salmonella-based anti-pneumococcal vaccine (for the prevention of pneumonia) developed by Biodesign Institute’s Center for Infectious Disease and Vaccinology was observed in-flight. By understanding gene expression in space, they hope to modify this and potentially other vaccines to enhance their protective properties on earth. This research has illuminated the inner workings of pathogenic cells through manipulation of gene expression and cellular mechanics by microgravity (or the condition of next to nothing gravitational force). It wasn’t until Nickerson’s spaceflight research, that certain behaviors of salmonella were observed.

Researchers estimate that around 94 million salmonella infections occur around the world each year, resulting in 155,000 deaths. Salmonella infection represents not only a useful vehicle for biomedical research concerning common genetic expression and cellular modularity using microgravity, but is a common, potentially fatal infection without a vaccine. It is estimated that the economic loss is $2 billion in the US alone resultant from salmonella-induced gastroenteritis.  

Infection with salmonella bacteria can occur through contaminated food, water, or by contact with an infected animal. Symptoms include diarrhea, fever, and abdominal cramps 12 to 72 hours post-infection. Lasting four to seven days, the infection generally runs its course, with healthy individuals recovering without treatment. However, the infection may be more severe in vulnerable populations, such as the very young and the elderly. In some cases, the diarrhea can be so severe that hospitalization is needed. Without proper antibiotic treatment, the infection may spread from the intestines to the blood stream and other parts of the body in which case death can occur.

No vaccine is available, but simple preventative measures are effective. Fully cooking poultry, ground beef, and eggs, and not consuming unpasteurized milk is recommended. It is important to clean cooking surfaces and wash your hands with soap and water after coming in contact with raw meat or poultry. It is also important to wash after handling reptiles, birds, or animal feces. 

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