The effect of α particles on one of the simplest unicellular organisms, Synechocystis sp. PCC 6803 cyanobacteria, is studied using a 120 cm cyclotron. Suspensions of cells are irradiated in a cuvette with walls made of thin mylar films. The energy of α particles in the solution is 24 MeV. The linear energy transfer (LET) of α particles is close to that of relativistic nuclei of the neon-magnesium group in galactic cosmic rays, making it possible to simulate their effect on biological objects. A number of apparent changes in the Synechocystis spectral characteristics are found for samples irradiated in and outside a hypomagnetic field.

not peer-reviewed) is the author/funder. All rights reserved. No reuse allowed without permission.The copyright holder for this preprint (which was . http://dx.doi.org/10.1101/281386 doi: bioRxiv preprint first posted online Mar. 13, 2018; Cyanobacteria survived the Foton-M4 space mission 2 It is now generally accepted that cyanobacteria are responsible for production of oxygen, which led to the so-called "Great Oxygenation Event". Appearance of dioxygen in Earth's atmosphere resulted in formation of the ozone layer and the ionosphere, which caused significant reduction of ionizing radiation levels at the surface of our planet. This event not only increased biological diversity but also canceled the urgency of previously developed mechanisms of DNA protection, which allowed to survive and develop in harsh environmental conditions including exposure to cosmic rays. In order to test the hypothesis if one of the oldest organisms on Earth retained ancient protection mechanisms, we studied the effect of ionizing radiation (IoR, here: α-particles with a kinetic energy of about 30 MeV) and space flight during the mission of the Foton-M4 satellite on cells of Synechocystis sp. PCC6803. By analyzing spectral and functional characteristics of photosynthetic membranes we revealed numerous similarities between cells exposed to IoR and after the space mission. In both cases, we found that excitation energy transfer from phycobilisomes to photosystems was interrupted and the concentration of phycobiliproteins was significantly reduced. Although photosynthetic activity was severely suppressed, the effect was reversible and the cells were able to rapidly recover from stress under normal conditions.Moreover, in vitro experiments demonstrated that the effect of IoR on isolated phycobilisomes was completely different from such in vivo. These observations suggest that the actual existence and the uncoupling of phycobilisomes under irradiation stress could play specific role not only in photo-, but also in radioprotection, which was crucial for early stages of evolution and the development of Life on Earth.

No abstract

No abstract