"Diversity is generally associated with a healthy ecosystem," said the microbiologist at the University of California at Davis. A diverse population of microscopic inhabitants is probably a signature of a healthy spacecraft, he added. And as humanity considers even longer undertakings in space – such as an 18-month trip to Mars – scientists must understand who these microbes are.
Samples for the Coil paper were collected in 2014 as part of the citizen science program MERCCURI Project. The initiative, conceived by a group of cheerleaders of the National Football League and the National Basketball Association who are also scientists and engineers, involved cleaning dozens of professional sports stadiums, identifying the microbes in the samples and sending those species to the ISS. to see if it would prosper (Bacillus aryabhatti, collected on a football practice field used by the Oakland Raiders, grew faster.)
In return, the UC Davis scientists who partnered on the project asked the astronauts of the ISS to clean the space station and return the samples to Earth. It seems like fair trade.
Samples were taken from 15 sites at the station, including the microphone of the audio terminal unit, air vents, the tab used to close the privacy panel in the crew sleeping compartment. These locations correspond in general to the places that are in a land home: the audio terminal unit is like a telephone; the air outlets, which absorb dust and dirt, are similar to the thresholds of the doors where the dust bunnies meet; the tab on the privacy panel vaguely resembles the knob on the door of his bedroom.
Microbe samples were packed and shipped to Earth, where UC Davis scientists sequenced their genomes. In each sample, they identified between 1,036 and 4,294 operational taxonomic units, a biological measure used to classify closely related organisms that roughly reflect the number of species. They then compared what they found with the results of surveys of the microbiomes of humans and their homes.
The study did not reveal "Andromeda strains" that threaten the well-being of astronauts; The ISS was dominated by microbes associated with humans, particularly the type that inhabits the skin. (On the other hand, the sequencing technique that scientists used can only identify species that are already known, so the study does not rule out the extremely unlikely possibility that there is something strange up there.)
"Honestly, I was not very surprised at all by the findings, "said microbiologist Jenna Lang, the first author of the study. Because all the equipment that goes into space is completely sterilized, any germ that colonizes the space station must travel with an astronaut.
"I expected the surfaces of the ISS to resemble human skin and … the upper airway, which did, for the most part, did it," said Lang.
The main difference was in the relative abundance of the species. For example, the ISS hosts more Staphylococcus than a typical home. But Lang cautioned that this study is based on a relatively small number of samples, all taken at a single point in time. When the crew of the ISS changes, it is likely that the microbes of the station also change.
It is important to control what germs are circulating there, said Coil. An unhealthy microbiome in the ISS could quickly lead to unhealthy astronauts. He noted that when the Russian Mir space station was decommissioned, it smelled of vapors of black mold that bloomed behind the panels and inside the air conditioning equipment. Some researchers even worried that Mir's microbes might have mutated into a biological risk when the space station returned to Earth in 2001 (Spoiler: Everything was fine).
"Now the questions are a little more nuanced," said Coil. "The science of the microbiome has advanced a lot." Scientists want to know what happens to the good microbes in astronauts, including the intestinal bacteria that help with digestion, and how those bugs will interact with the microbiome of the space that surrounds them.
"There are many much larger studies going on now asking these bigger questions," said Coil. "Ours is more preliminary information."
You are surrounded by a cloud of bacteria as unique as a fingerprint
Author information: Sarah Kaplan is a journalist for Speaking of Science.