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Space Station Microbes Similar to Those Found in Houses

NEW YORK (GenomeWeb) – The microbes on the International Space Station most closely resemble those found within people's homes, according to a new sequencing study.

Astronauts swabbed more than a dozen sites within the space station to gather microbial samples that a University of California, Davis-led team of researchers then amplified and sequenced as part of citizen-academic scientist Project MERCCURI. As they reported in PeerJ today, the researchers compared the ISS microbes to those found in people's homes and on their bodies. While differing from both, the ISS microbes were more similar to those found in people's houses.

"[W]e are completely surrounded by mostly harmless microbes on Earth, and we see a broadly similar microbial community on the ISS," author David Coil from UC Davis said in a statement.

The researchers selected 15 sites on the space station for the astronauts there to sample. These sites were largely analogous to sampling sites from the Wildlife of Our Homes project. For instance, while that project examined sites like cell phones and doorsills that gather dust, the ISS study sampled lab microphones and vents that collect dust.

The samples were collected and returned to Earth for 16S rDNA gene amplification and sequencing on the Illumina MiSeq platform. After filtering, the researchers uncovered 12,554 operational taxonomic units.

This, the researchers noted, is more than previous pyrosequencing-based microbial studies of the space station had uncovered, which they attributed to the greater sequencing depth they now achieved. One of the earlier studies reported that more than 90 percent of the microbes it uncovered belonged to four bacterial genera, but the UC Davis-led team found that those four genera — Corynebacterium, Propionibacterium, Staphylococcus, and Streptococcus — made up slightly less than a quarter of their data. The Davis team also reported finding archaea, while the previous two studies did not.

The Davis-led team reported that the 19 most abundant orders in their study encompass nearly 94 percent of their data and that, within each order, the most common genus present was human associated. This, the researchers noted, was not surprising as the sources of microbes for the space station are incoming cargo and crew.

The researchers cautioned that their analysis can't determine whether the microbes they detected were viable. Still, they reported that the microbes sampled on the space station were highly similar, no matter where in the station they were collected. However, the starboard crew and aft lab vents did differ from the other samples. Their most abundant families were Bacteroidaceae, Ruminococcaceae, and Verrumicrobiaceae and Rikenellaceae, Bacteroidales S24-7, and Lactobacillaceae, respectively.

When the Davis team compared the microbes they found to those that the ‘‘Wildlife of Our Homes’’ project found to lurk in people's houses, they found the sets to be significantly different. The Davis team noted that Earth-bound houses have a greater number of microbial sources, such as outdoor air, tracked-in dirt, pets, and plants, as compared to the space station's controlled deliveries, and suggested that the crew themselves were the likeliest sources of microbes.

But when they folded in data from the Human Microbiome Project, all three sets differed. However, in this meta-analysis, the ISS samples were significantly more similar to the home samples than to the HMP samples. The starboard crew vent sample that differed from other ISS samples, though, was more similar to the gastrointestinal HMP samples.

"The microbiome on the surfaces on the ISS looks very much like the surfaces of its inhabitants, which is not surprising, given that they are the primary source," first author Jenna Lang said in a statement. "We were also pleased to see is that the diversity was fairly high, indicating that it did not look like a 'sick' microbial community."