A microbial survey of the most extreme built environment: the International Space Station (ISS)

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Proposed titles:

Bacterial survey of high-touch surfaces on the International Space Station (ISS)

Unseen Companions: A Bacterial Survey of the International Space Station (ISS)

Who is up there? A Bacterial Survey of the International Space Station (ISS)

A microbial survey of the most extreme built environment: the International Space Station (ISS)
[Just wanted to get "ISS" in this rather attention getting title line]




Modern advances in sequencing technology have enabled the census of microbial members of many natural ecosystems. Recently, attention is increasingly being paid to the microbial residents of human-made, built ecosystems, both private (homes) and very public (subways, office buildings, and hospitals). Here, we report results of the characterization of the microbial ecology of a singular built environment, the International Space Station (ISS). This ISS sampling involved the collection and microbial analysis (via 16S rDNA PCR) of 15 samples swabbed from surfaces onboard the ISS. This sampling is a component of Project MERCCURI - a collaborative effort of the "microbiology of the Built Environment network" (microBEnet) project, Science Cheerleaders, NanoRacks, Space Florida, and Scistarter.com. Learning more about the microbial inhabitants of the "buildings" in which we travel through space will take on increasing importance, as plans for human exploration and colonization of the solar system come to fruition.

Methodology/Principal Findings

Sterile swabs were used to sample 15 surfaces onboard the ISS. The sites sampled were designed to be analogous to samples collected for 1) the Wildlife of Our Homes project and 2) a study of cell phones and shoes that were concurrently being collected for another component of Project MERCCURI. Sequencing of the 16S rRNA genes amplified from DNA extracted from each swab was used to produce a "census" of the microbes present on each surface sampled. We compared the microbes found on the ISS swabs to those from both the Earth homes and the Human Microbiome Project.


While significantly different from homes on Earth and the Human Microbiome Project samples analyzed here, the microbial community composition on the ISS was more similar to home surfaces than to the human microbiome samples. The ISS surfaces are species-rich with 1036-4294 operational taxonomic units (OTUs per sample). There was no discernible biogeography of microbes on the 15 ISS surfaces, although this may be a reflection of the small sample size we were able to obtain.

There is a growing appreciation of the importance of microbial communities found in diverse environments from the oceans, to soil, to the insides and outsides of plants and animals. Recently, there has been an expanding focus on the microbial ecology of the "built environment" - human constructed entities like buildings, cars, and trains - places where humans spend a large fraction of their time. One relatively unexplored type of built environment is that found in space. As humans expand their reach into the solar system, with more and more plans for space travel, and with the possibility of the colonization of other planets and moons, it is of critical importance to understand the microbial ecology of the built environments being utilized for such endeavors.

Interest in the microbial occupants of spacecraft long precedes the launch of the International Space Station (ISS) (Trexler 1964)(Silverman 1971). Early work primarily focused on ensuring that the surfaces of spacecraft were free of microbial contaminants in an effort to avoid inadvertent panspermia (seeding other planets with microbes from Earth) (Pierson 2007). Work on human-occupied spacecraft such as Mir, Space Shuttles, and Skylab focused more on microbes with possible human health effects. With the launch of the ISS, it was understood that this new built environment would be permanently housing microbes as well as humans. Calls were made for a better understanding of microbial ecology and human-microbe interactions during extended stays in space (Pierson 2007) (Roberts 2004) (Ott 2004). Efforts were made to establish a baseline microbial census. For example, Novikova et al (Novikova 2006) obtained more than 500 samples from the air, potable water, and surfaces of the ISS, over the course of 6 years.

These early studies were unavoidably limited by their reliance on culturing to identify microbial species. Culture-independent approaches were eventually implemented, including some small-scale 16S rDNA PCR surveys (Castro 2004),(Moissl 2007) and the Lab-On-a-Chip Application Development Portable Test System (LOCAD-PTS) (Maule ), which allows astronauts to test surfaces for lipopolysaccharide (LPS - a marker for Gram negative bacteria). Originally launched in 2006, the capability of the LOCAD-PTS was expanded in 2009 to include an assay for fungi (beta-glucan, a fungal cell wall component) and Gram positive bacteria (lipoteichoic acid, a component of the cell wall of Gram positive bacteria.) Recently, the first large-scale, culture-independent 16S rDNA PCR survey was published using the Roche 454 platform, looking at dust on the ISS (Venkateswaran 2014). We report here on a further effort involving 16S rDNA PCR and sequencing, using the Illumina platform, to examine the microbial communities found on 15 surfaces inside the International Space Station.

The microbial census of ISS surfaces presented here is a component of a larger project (Project MERCCURI) which was undertaken for both scientific reasons as well as for its outreach and education potential. Project MERCCURI (Microbial Ecology Research Combining Citizen and University Researchers on the ISS) is a collaborative effort involved the "microbiology of the Built Environmnet network" (microBEnet), Science Cheerleader, NanoRacks, Space Florida, and Scistarter.com. Other parts of Project MERCCURI include a project studying the growth of cultured microbes on the ISS and a project examining the diversity of microbes on cells phones and shoes from public participants are diverse events around the United States. He we focus solely on the microbial survey of surfaces onboard the ISS.

The 15 surfaces sampled on the ISS were chosen by the Project MERCCURI team in an effort to make them analogous to 1) the surfaces sampled for the "Wildlife of Our Homes" project (homes.yourwildlife.org), which asked citizen scientists to swab nine surfaces in their homes, and 2) cell phone and shoe swab samples that were also being collected via Project MERCCURI. The motivation for choosing the sites in this way was both to increase public awareness of the microbiology of the built environment, as well as to begin to compare the microbial ecology of homes on Earth with the only current human home in space. We also present a comparison of the ISS swab results with data from 13 human body sites sampled via the Human Microbiome Project. This comparison was done to example the potential human contribution to the microbial life on the ISS.


Surfaces swabbed:

Astronauts were asked to swab 15 surfaces on the International Space Station. Below are their verbatim instructions.

  1. Audio Terminal Unit (telephone) hand held push-to-talk microphone located in the forward portion of the US Lab Module

  2. Audio Terminal Unit (telephone) hand held push-to-talk microphone located in the aft portion of the US Lab Module

  3. US Lab Robotic Work Station laptop PC keyboard used to control the robotic arm

  4. US Lab Robotic Work Station hand controller used to control the movement of the robotic arm

  5. US Lab Robotic Work Station foothold, left side

  6. US Lab Robotic Work Station foothold, right side

  7. One of the main laptop keyboards in the US Lab used to control science experiments and the systems of the space station

  8. One of the vertical handrails on the equipment racks inside the US Lab