Microbial biodiversity assessment of the European Space Agency's ExoMars 2016 mission

The ExoMars2016 mission, consisting of the Trace Gas Orbiter (TGO) and the Schiaparelli lander, was launched on the 14 March 2016 from Baikonur, Kazakhstan. The Schiaparelli lander was subject to strict requirements for microbial cleanliness according to the Committee on Space Research (COSPAR) planetary protection policy to avoid contamination of the Mars environment. To reach the required cleanliness, newly built microbiologically controlled cleanrooms and clean environment were used for the assembly, integration and testing of the ExoMars2016 flight hardware. We performed a microbiological survey of the controlled cleanroom at Thales Alenia Space in Turin, Italy, where the majority of assembly and integration activities were carried out for the Schiparelli lander. Besides the ESA standard bioburden assay to determine a proxy for the microbiological contamination of the flight hardware, we performed various alternative cultivation assays and utilized molecular techniques, including qPCR and next generation sequencing, to assess the quantity and identities of bacterial and archaeal signatures in the cleanroom.The studied cleanrooms and change room were occupied by very distinct microbial communities. Most of the bacteria were human associated or bacteria carrying various resistances, but the analyses revealed separate microbiomes: the change room showed higher microbial abundance and diversity, and certain bacteria, including human skin associated Propionibacterium, were more abundant in the change room. The so called alternative cultivation assays proved important in detecting the whole cultivable diversity. The results also show that the bioburden, detected microbial contamination and microbial diversity decreased during the assembly, integration and testing period after the cleanroom was decontaminated with more effective cleaning agents. During the whole project, the bioburden stayed at acceptable level and did not raise any concern for the ExoMars2016 mission. The cleanroom complex at Thales Alenia Space in Turin is an excellent example of how efficient microbiological control can be performed.