Insights into the microbial diversity and bioburden in a South American spacecraft assembly clean room

In this study, samples from the spacecraft assembly clean room BAF (final assembly building), located at Centre Spatial Guyanais in Kourou, French Guiana, were characterized by qualitative and quantitative methods to determine the bioburden and biodiversity. The cultivation assays mainly focused on extremotolerant microorganisms that have special metabolic skills, such as the ability to grow without oxygen, fix nitrogen, grow autotrophically, or reduce sulfate. A broad range of media and growth conditions were used to simulate possible extraterrestrial environments and clean room buildings. In addition to these alternative cultivation assays, the ESA standard protocol for bioburden estimation was also applied. The phylogenetic analysis of the isolates (mainly facultative anaerobes) showed an extraordinarily broad cultivable biodiversity. Overall, 49 species were isolated and identified as members of the bacterial phyla Actinobacteria, Firmicutes, α-, β-, γ-Proteobacteria, and Bacteroidetes/Chlorobi. In addition to cultivation-based analyses, molecular techniques were also applied, including construction of a 16S rRNA gene clone library. The results indicate a wide-ranging microbial diversity (12 bacterial phyla, 34 families) that not only confirms the results of the cultivation efforts but also deepens our understanding of the noncultivable variety. Our investigations hint at a very broad, mainly uncultivated microbial diversity.