Perspectives on the direction of space microbiology for human health and habitat sustainability

Microbes populate every corner of the Earth and accompany humans wherever they travel, including space.  Microbes also play a critical role in maintaining the balance between health and disease.

In a comprehensive new review, researchers at Arizona State University, NASA, and a team of national experts explore the behavior and importance of microbes under the low gravity conditions of spaceflight. 

This review provides a thorough analysis of past and current human spaceflight microbiology, including efforts to safeguard the health of astronauts, their habitats and life support systems as ambitious missions are planned to the Moon and Mars, and commercial spaceflights carry civilian space travelers to Earth’s orbit.  In addition, current challenges of spaceflight microbiology research, evolving technologies used to perform these experiments, a vision for the future of this field, and relevance to human health on Earth are discussed.

“With the rapid expansion of NASA’s human deep space exploration plans, in parallel with military and commercial human spaceflight missions, understanding lessons learned from decades of space microbiology research and operations to protect the health of space travelers and their habitats is critical for future mission success and translational advances for the public,” says Cheryl Nickerson, first author of the review.

Nickerson is a researcher in the Biodesign Center for Fundamental and Applied Microbiomics, a professor with ASU’s School of Life Sciences, and Co-Leader of the ASU Space Life Sciences and Health Initiative. 

In addition to ASU collaborators, Nickerson is joined by researchers from NASA, Texas State University, JES Tech, Purdue University, and Baylor College of Medicine.

The review appears in the upcoming issue of the journal Microbiology and Molecular Biology Reviews and received the cover image for this issue, which was designed by Jennifer Barrila, an ASU co-author on the study. 

Microbes on the move

The extraordinary adaptability of microorganisms is one of the most remarkable attributes of living systems, enabling them to flourish in virtually every ecological niche, including spacecraft.

While microbes perform a myriad of tasks essential to life, some also cause disease and degrade the structural integrity of habitats. Nickerson’s research group has been at the forefront of these investigations, exploring the behavior of infectious pathogens and the responses of infected cells, under conditions of reduced gravity.  They discovered the threat posed by some microbes unexpectedly changes when removed from the stability of Earth's gravity in which they arose and evolved. Research into the cause of these changes during spaceflight can provide a better understanding of our health and environment on Earth that cannot be observed under normal gravity conditions.

Human health and habitat sustainability are critical components of the rapidly growing spaceflight industry, now valued at over $500 billion annually. The spaceflight environment can profoundly affect human health in a variety of ways, and the role of microorganisms during spaceflight is an integral component to consider for spaceflight missions. For example, spaceflight acts to downgrade aspects of the body’s immune system, potentially leaving space travelers more vulnerable to ailments, including infectious disease.

Microgravity and fluid flow

While more research needs to be done, a great deal of evidence indicates that the response of cells to spaceflight conditions is not directly caused by reduced gravity, referred to as microgravity.  Rather, pioneering research from Nickerson and her longtime collaborator Mark Ott at the NASA Johnson Space Center, suggests the reduced physical/mechanical forces in the quiescent environment of microgravity, are the stimuli that may drive many of the unexpected responses observed during spaceflight.

A key example of this type of “mechanotransductive” response happens both on Earth and in space when fluid flows over the surface of microbial and human cells. This creates a mechanical force called fluid shear which can induce a wide range of cellular responses, including growth, movement, and maintaining the balance between health and disease.

Among the unexpected cellular transformations observed, Nickerson’s team found reduced fluid shear can heighten microbial virulence, increase the ability of microbes to infect human cells, increase stress resistance, alter microbial gene expression, and increase the ability of bacteria to form biofilms (gooey communities of cells). These biofilms complicate efforts to maintain clean and safe environments aboard spacecraft, causing corrosion to life-support components and degrading other onboard materials.

Low fluid shear conditions are also relevant to microbial lifestyles on Earth because they mimic certain natural environments where microbes thrive, such as in the human gastrointestinal and respiratory tracts and mimic similar behaviors as pathogens subjected to microgravity in space.

Earth and space

Past incidents, like the severe Pseudomonas bacterial infection suffered by an Apollo 13 astronaut and the recovery of Salmonella from crew trash on the Space Shuttle highlight the urgent need to understand infectious diseases in spaceflight environments.

As crewed missions to the Moon, Mars, and beyond become a reality, understanding microbial behaviors will be crucial for maintaining astronaut health and ensuring the sustainability of their space habitats. The research described in the new reviewarticle also promises to advance fundamental knowledge concerning the microbiology of health and habitats on Earth.