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#Introduction  There is a growing appreciation of the importance of communities of microbes found in diverse environments from the oceans, to soil, to the insides and outsides of various plants and animals. Recently there has been an expanding focus on the microbial ecology of the "built environment" - those human constructed entities like buildings, cars, ships and planes - places where we spend a large fraction of our time. One somewhat unexplored - yet certainly important - 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 possible colonization of other planets and moons, we believe 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 \cite{11883448}\cite{5173646}. Early work primarily focused on ensuring that spacecraft were free of microbial contaminants in an effort to avoid inadvertent panspermia (seeding other planets with microbes from Earth.) With the launch of the ISS, it was clear that this new built environment would be 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 \cite{pierson2007microbial} \cite{14994179} \cite{14569419}. Efforts were made to establish a baseline microbial census. For example,  Novikova et al \cite{16364606} obtained more than 500 samples from the air, potable water, and surfaces of the ISS, over the course of 6 years. While Because we know that most microbes are recalitrant to culture, we know that  these earliest studies were limited by their reliance on culturing to identify microbial species. Culture-independent approaches were eventually implemented, including 16S rDNA PCR surveys \cite{14749908} and the Lab-On-a-Chip Application Development Portable Test System (LOCAD-PTS), 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 gram positive cell wall component.) This year, the first large-scale, culture-independent 16S RDNA PCR survey was published using the Roche 454 platform \cite{24695826}. We report here on an additional a further  effort to use 16S rDNA PCR sequencing sequencing,  on the Illumina platform platform,  to examine the microbial communities found on 15 surfaces inside the International Space Station. We have also compiled a collection of such papers in an online resource to provide a more comprehensive historical perspective of this kind of work (see http://www.mendeley.com/groups/844031/microbiology-of-the-built-environment/papers/added/0/tag/space/).   This microbial census of ISS surfaces is a component of a larger  project (Project MERCCURI,) which  was done not just for the science but also for its outreach and education potential. SAY MORE ON THIS... Project MERCCURI (Microbial Ecology Research Combining Citizen and University Researchers on the ISS) is collaborative effort of UC Davis (microBEnet), Science Cheerleader, NanoRacks, Space Florida, and Scistarter.com. Project MERCCURI includes three components. Aim 1 involves collecting microbes (by swabbing surfaces) from sporting venues and other high-profile built-environment locations. This component included a concurrent outreach effort in which 2000 "Citizen Scientists" were asked to collect microbes from their cell phones and shoes using sterile swabs. These swabs were sent to the Earth Microbiome Project lab for microbial community analysis. Aim 2 is a bacterial growth assay, in which non-pathogenic microbes collected from the surfaces in Aim 1, "compete" against each other, both on the surface of the Earth (at UC Davis) and onboard the ISS. For Aim 3, the results of which are presented here, astronauts were asked to swab 15 surfaces onboard the ISS to collect microbes for DNA-sequenced-based identification, a service also provided by the Earth Microbiome Project.  The 15 surfaces onboard the ISS were chosen by the Project MERCCURI team in an effort to make them analogous to 1) the surfaces sampled with the "Wildlife of Our Homes" project, which asked citizen scientists to swab nine surfaces in their homes, and 2) the cell phone and shoe samples that were being collected via Project MERCCURI. The motivation for choosing the sites in this way was both to increase public engagement with the data, as well as to begin to compare the microbial ecology of our homes on Earth with our only home in space. Because the cell phone and shoe sequence data associated with this project are not available at this time, we will include those comparisons in a future publication. However, we have included comparisons to two other relevant citizen science projects: Belly Button Biodiversity and Armpit Life. These two projects were selected to represent the human contribution to the microbial life on the ISS.