deletions | additions       diff --git a/Introduction.md b/Introduction.md  index 14f879d..8c034b8 100644  --- a/Introduction.md  +++ b/Introduction.md 
...
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.   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 rDNA  PCR survey was published using the Roche 454 platform platform, looking at dust on the ISS  \cite{24695826}. We report here on a further effort to use 16S rDNA PCR sequencing, on the Illumina 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/).