Horizontal gene transfer in space preparation of the ISS experiment Bacterial Conjugation

Abstract

Horizontal gene transfer (HGT) enables microorganisms to transmit genetic information to neighboring cells. On Earth, different mechanisms of HGT are known, namely conjugation, transduction and transformation. Most importantly, the mechanism of conjugation permits bacteria to adapt rapidly to environmental conditions, for example by conveying antibiotic resistances. This advantageous ability poses a huge threat to humans on Earth as well as in space as multi-resistant strains are on the rise and only few new antibiotics are being discovered. In regard to long-term space missions, the danger of microorganisms developing antibiotic resistances is an even more crucial factor for the health of astronauts as they can only rely on limited medical support. While the driving force behind emerging antibiotic resistances through bacterial conjugation has been thoroughly studied on Earth, its exploration in the unique environment of space remains limited. The “Bacterial Conjugation in Space” experiment is a microscope-based experiment that will utilize the live fluorescent microscopic imaging facility (FLUMIAS Microscope) on board the International Space Station (ISS). The campaign aims to shed light on bacterial conjugation in microgravity. To track the conjugation microscopically, plasmids that will express different fluorophores will be introduced into the model organism Escherichia coli. The results of these experiments will be of high importance to ensure the safety and health of astronauts during future long-term missions. However, the heavy technical and experiment constraints imposed by space station environment require a meticulous planning and procedure development to guarantee a campaign with significant results. This study shows the results of the experiments that determine the optimal growth conditions and the negative impact on the conjugation rate due to the experiment setup. Additionally, it presents s a proof of principle for the detection of transconjugants as well as the detectability of the fluorophores and transconjugants and the ability of the donor strain to retain the conjugative plasmids during possible storage periods. Moreover, the study provides a preliminary sample preparation procedure to enable the planned space experiment and provides a proof of concept for the setup within the set of experimental and technical constraints.