Komagataeibacter oboediens changes outer membrane vesicle-associated activities after exposure on the International Space Station

Abstract

Outer membrane vesicles (OMVs) carry various biomolecule cargo, including enzymes, and communicate with the surrounding via them. The role of the enzyme-associated OMVs from food-grade bacteria in human health and disease is not clear, in particular, after the impact of stressful factors (changed gravity and atmosphere, UV-radiation) in the context of astronauts' diet. Aim. We researched OMVs of Komagataeibacter oboediens isolated from kombucha microbial community samples exposed to the space/Mars-like stressors simulated on the International Space Station and cultivated within a five-year period to know more about their behaviour with biomolecules and mammalian cells. Methods. A series of in vitro experiments on the RNA cleavage, DNA and RNA transcription inhibition and cytotoxic assay with OMVs/ Komagataeibacter were conducted. SignalP 6.0 was used for detecting signal peptides in predicted ribonucleases in K. oboediens genome, and ProtComp Version 9 served for identifying RNase sub-cellular location. Results. The behaviour of OMVs in bacteria before and after an impact of stressful conditions differed, relying on differences in associated nucleolytic activity, the inhibitory capabilities against the T7 bacteriophage RNA polymerase and Taq DNA polymerases and a cytotoxic effect, despite identical nucleotide sequences in homologous genes. The in vitro inhibition of RNA and DNA transcriptions was less pronounced in OMVs of exposed bacteria than in vesicles of the ground-based strain. It correlated with a lower RNase activity and a loss of cytotoxicity towards human malignant cells, even five years after the flight. Bacterial RNase I was predicted to be located in the OMV periplasm. Conclusion. Komagataeibacter's OMV-associated activities were modified after exposure to the International Space Station and inherited in a non-genetic manner. K e y w o r d s:Outer membrane vesicles, stressful factors, RNase I.