August 16, 2013
NASA Study Looks At How Spaceflight Affects Bacterial Social Networks
April Flowers for redOrbit.com - Your Universe Online
Microorganisms are invisible to the naked eye. Healthy human adults have ten times as many microbial cells as human cells inside their bodies. Countless more microbes populate the environment around us, which means when astronauts launch into space, a microbial entourage follows.
Communities of bacteria, known as biofilms, are often found attached to surfaces. The biofilms protect the bacteria with a slimy matrix they secrete. For example, if you want to experience what a biofilm feels like, skip brushing your teeth tomorrow.
One of NASA’s primary goals is to minimize health risks astronauts might experience in extended spaceflight. It is essential that methods for preventing and treating spaceflight-induced illnesses be developed before astronauts set off on long-duration space missions. NASA scientists need to learn how bacterial communities that play roles in human health and disease are affected by spaceflight.
Biofilms made by Pseudomonas aeruginosa were cultured on Earth and in space during two studies funded by NASA – Micro-2 and Micro-2A. The goal was to determine the impact of microgravity on the bacteria’s behavior. An opportunistic human pathogen, P. aeruginosa is commonly used for biofilm studies.
Biofilms grown aboard the International Space Station (ISS) were compared with those grown on the ground. This comparison revealed, for the first time, spaceflight changes the behavior of bacterial communities.
Most bacterial biofilms are harmless. Some, however, threaten human health and safety. They can exhibit increased resistance to the immune system's defenses or treatment with antibiotics, or damage vital equipment aboard spacecraft by corroding surfaces or clogging air and water purification systems that provide life support for astronauts. Similar problems are caused by biofilms on Earth.
"Biofilms were rampant on the Mir space station and continue to be a challenge on the International Space Station, but we still don't really know what role gravity plays in their growth and development," said Cynthia Collins, PhD, assistant professor in the Department of Chemical and Biological Engineering at the Center for Biotechnology and Interdisciplinary Studies at the Rensselaer Polytechnic Institute in Troy, NY. "Before we start sending astronauts to Mars or embarking on other long-term spaceflight missions, we need to be as certain as possible that we have eliminated or significantly reduced the risk that biofilms pose to the human crew and their equipment."
The experiments took place in 2010 and 2011 during the STS-132 and STS-135 missions aboard space shuttle Atlantis. Scientists on Earth and in space performed nearly simultaneous parallel experiments culturing samples of P. aeruginosa bacteria using conditions that encouraged biofilm formation.
Identical sets of hardware developed for growing cells in space were used for both experiments. According to Collins, "artificial urine was chosen as a growth medium because it is a physiologically relevant environment for the study of biofilms formed both inside and outside the human body."
A specialized fluid processing apparatus composed of glass tubes divided into chambers was used to culture the biofilms. Each tube was loaded with a membrane that provided a surface on which the bacteria could grow; the artificial urine was used for the bacteria's nourishment. P. aeruginosa samples were loaded into separate chambers within each tube.
Once prepared, the tubes were placed in groups of eight inside a device called the group activation pack (GAP). The GAP is designed to activate all of the bacterial cultures at once. Identical GAPs were prepared for the concurrent spaceflight and ground experiments.
On board the shuttle, the astronauts initiated the experiments by operating the GAPs and introducing the bacteria to the artificial urine medium. On Earth, the research team performed the same operations with the control group of GAPs at NASA's Kennedy Space Center. The GAPs in both situations were housed in incubators to maintain temperatures appropriate for bacterial growth.
When the microgravity samples were returned to Earth, researchers examined them for a number of factors. These included the thickness of the biofilms, the number of living cells and the volume of biofilm per area on the membranes. In addition, the team used a microscopy technique that allowed them to capture high-resolution images at different depths within the biofilms, revealing details of their three-dimensional structures.
The findings showed that the P. aeruginosa biofilms grown in space contained more cells, more mass and were thicker than the control biofilms grown on Earth. Reviewing the microscopy images of the space-grown biofilms revealed a unique, previously unobserved structure consisting of a dense mat-like "canopy" structure supported above the membrane by "columns." In contrast, the Earth-grown biofilms were uniformly dense, flat structures. These findings provide the first evidence the community level behavior of bacteria is affected by spaceflight.
In microgravity, microbes experience “low shear” conditions that resemble conditions inside the human body but are difficult to study. Collins notes, "Beyond its importance for astronauts and future space explorers, this research also could lead to novel methods for preventing and treating human disease on Earth. Examining the effects of spaceflight on biofilm formation can provide new insights into how different factors, such as gravity, fluid dynamics and nutrient availability affect biofilm formation on Earth. Additionally, the research findings one day could help inform new, innovative approaches for curbing the spread of infections in hospitals."
Micro-2 and Micro-2A were funded by NASA’s Space Biology Program. Experiments in related space biology continue aboard the ISS, including recently selected studies that are planned for future launch to the orbiting laboratory.
Microbial communities will faithfully follow us wherever we go, including space, making this evidence of the effects of spaceflight on bacterial physiology relevant to human health. The difference in behavior between Earth-bound biofilms and spaceflight biofilms is critical information as NASA strives to keep astronauts healthy and safe during future long-duration space missions.
Image Below: P. aeruginosa biofilm cultured during spaceflight. Credit: Rensselaer Polytechnic Institute