Biofilms are multispecies, densely aggregation of cells that clump together to form a residue on surfaces. Biofilms can be resistant to antimicrobials, and are notoriously difficult to clean up. They can lead to a variety of health problems and have a corrosive affect on many materials including stainless steel. This makes them a danger to the water supply system at the ISS. Credit: Arizona State University's Biodesign Institute
The universe beyond Earth appears vast and lonely. However, there will always be plenty of microbes wherever humans travel.
Jiseon Yang, Arizona State University Biodesign Institute Center for Fundamental and Applied Microbiomics' lead author, and her collaborators characterized different bacterial populations taken from drinking water from the International Space Station (ISS) in a unique study.
Although historical monitoring of the ISS water system was focused on identifying microbial species through both culture-dependent (genome sequencing), and independent (genome sequencing), methods that identify microbial species have not been able to accurately predict the function of microbial communities. It is crucial to understand microbial function in order to protect the integrity of mission-critical spacecraft lifesupport systems and astronaut health.
Yang and her colleagues investigated the functional properties of waterborne bacterial isolates taken from the ISS's potable water system. These samples were collected over many years. This study was designed to increase our understanding of the effects of long-term spaceflight exposure on microbial characteristics. This is a crucial issue that must be addressed, since microgravity adaptations have been shown to drastically alter bacterial characteristics. Biofilms, which are dense bacterial aggregates, can also form in the ISS potable drinking water system, and could pose a threat to mission success.
Research into the behavior and function of mixed microbial communities is gaining popularity in the scientific community. These types of studies give insight into how microorganisms interact in real-world settings. These studies can provide important guidelines for the assessment and mitigation of microorganisms' risk to water systems on Earth and in space.
Yang says that polymicrobial interactions can be complex and not stable over time. "Our study provides detailed phenotypic analysis of single- and multiple-species bacterial isolates from the ISS water systems over multiple years. This allows us to understand long-term microbial interactions as well as adaptation to microgravity environments. Our study could improve the risk assessment of microbes in space- and earth-built environments.
Yang is joined by ASU colleagues Jennifer Barrila and Olivia King, who lead the Biodesign team. Also, co-authors Robert JC McClean from Texas State University and Mark Ott, and Rebekah Bruce, both of the NASA Johnson Space Center in Houston.
The journal npj Biofilms and Microbiomes has published the group's findings in its current issue.
Life is liquid
Water is essential for life on Earth as well as in space. Spaceflight requires water for drinking and hygiene. However, it is difficult to supply clean water reliably to astronauts.
NASA estimates that if the ISS could not recycle water, 40,000 lbs of water would have to be shipped from Earth each year to resupply four crewmembers. This is an exorbitant expense for their entire stay on the ISS.
The ISS's water purification system, also known as the Environmental Control and Life Support System (ECLS), is used to clean wastewater in a three-step process. After removing particles and debris from the water, it passes through multi-filtration beds that contain substances that remove both organic and inorganic impurities. The water is then filtered through a catalytic oxygen reactor to remove volatile organic compounds and kill microorganisms.
While sophisticated life-support systems are meant to protect this precious resource from contamination, bacterial communities have proven their resilience by forming biofilms in the ISS water recovery system.
The current study examined microbial activity in NASA-archived bacterial strains that were collected from the ISS water system over many years. The profiles of bacteria species included biofilm composition and structure, metabolism, hemolysis (ability lyse red cells), and antibiotic resistance.
Small and determined
Despite their small size, bacteria are still a formidable force to be taken seriously. Apart from their ability to cause various infectious diseases in humans and bacteria clumping together on surfaces can lead to dense multispecies aggregates called biofilms. These biofilms are resistant to antimicrobials.
Globally, bacteria biofilms have a significant socioeconomic impact. They also cause many industrial and health problems that can lead to billions of dollars in economic losses each year. These problems include fouling oil and chemical processes, encrusting medical stents and contaminating water sources. Biofilms can also cause corrosion in a wide range of materials. This includes the ability to degrade stainless steel (which is used in the ISS water systems).
These are the reasons why spaceflight presents a unique opportunity to manage biofilm formation and control bacteria in complex microbial ecosystems.
The NASA water recovery system continually generates potable water aboard the ISS from recycled urine, waste and condensation. It uses distillation, filtrations and iodine treatments.
Despite all these efforts, inflight analysis of water samples taken from the ISS potable drinking water system has revealed microbial levels exceeding NASA standards. This contamination is primarily caused by environmental flora in the water system.
Management of high-risk situations
Many of the same microbes that are found in water on Earth can also be found in ISS samples. However, it is possible that this unique environment could increase the dangers these organisms face. Particularly interesting are the microgravity conditions, which researchers from the same group previously demonstrated can increase the virulence of certain infectious microbes and their stress resistance, alter their gene expression profiles and encourage biofilm formation.
These issues are compounded by the fact that astronauts can experience immune suppression due to their time in space, making them more susceptible to microorganism infection.
Results from the current study showed that the ISS waterborne bacterial strains were resistant to several antimicrobial compounds including antibiotics. They also had distinct patterns of carbon utilization and biofilm formation. Burkholderia, a bacterial strain, also showed hemolytic activity. This makes it a potential threat to astronaut health.
The study of the interactions of bacteria species in this study revealed different patterns of behavior. Some of these were dependent on whether samples were taken in the same year as others, suggesting that adaptive processes are at work in microgravity. It is important to note that the dynamic phenotypes seen in this polymicrobial study could not have been predicted with sequencing technologies.
This study will provide insight into the challenges that spaceflight missions face in providing safe drinking water, especially for longer durations. This study could also provide valuable information that can be used to improve the functioning of engineered water systems in Earth for safety and industrial benefit.
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Jiseon Yang and colleagues, Longitudinal characterization of multispecies microbiomes recovered from spaceflight water, npj Microbiomes (2021). Jiseon Yang and colleagues, Longitudinal characterisation of multispecies microbial communities recovered from spaceflight water (2021). DOI: 10.1038/s41522-021-00240-5
