Is the repair kinetics of radiation induced DNA damages influenced by microgravity? Preparation of the space experiment LUX-in-Space

Kurzfassung

In space, all organisms are exposed to and affected by space radiation and microgravity. This applies for microorganisms, plants and animals used as components of bioregenerative life support systems, for cells, tissues and organoids investigated in scientific space experiments and for astronauts. Radiation and microgravity were identified as two of the five most important hazards for manned spaceflight. Therefore, the knowledge of biological space radiation effects as well as the impact of microgravity on enzymatic repair processes is mandatory for risk assessment, especially in view of long duration missions to Mars or permanently inhabited bases on the Moon. The repair kinetics of radiation induced DNA damages will be investigated with a bioassay, the DLR-developed SOS-Lux Test, in the space experiment LUX-in-Space on the ISS. Bacteria serve as model organisms. They possess the same type of nucleotid excision repair as all other living organisms including humans. Salmonella enterica subsp. enterica (ATCC 53648) cells are transformed with the pBR322-derived plasmid pPLS-1, carrying the promoterless lux operon of Photobacterium leiognathi as the reporter element controlled by a DNA damage-dependent SOS promoter as sensor element. Due to safety issues, UV radiation was chosen for DNA damage induction. It causes defined types of DNA damage, e.g. cyclobutan pyrimidine dimers, which are among those also induced by ionising radiation. In response to exposure to radiation the SOS promoter is activated. Due to the genetic modification, the connected so-called lux genes are expressed, resulting in the emission of measurable bioluminescence proportional to the applied dose of radiation. The DNA repair kinetics are followed by bioluminescence and optical density measurements. The experiment specific hardware for the BIOLAB facility is under development by industry and the results of the rigorous testing and optimisation program will be presented. LUX-in-Space is the first space experiment where the whole series of events from DNA damage induction in metabolically active cells to the different steps of enzymatic repair will take place in real microgravity and the repair kinetics will be monitored in situ by optical measurements. The effects of microgravity will be clearly separated from other spaceflight factors by comparison with parallel samples on an onboard 1g centrifuge in the Biolab facility on the ISS and in a parallel ground control experiment with identical samples in flight-identical hardware.