Alba Zanini

Ionizing radiation impacts photochemical quantum yield and oxygen evolution activity of Photosystem II in photosynthetic microorganisms.

Purpose: Long-term space exploration requires biological life support systems capable of coping with the deleterious space environment. The use of oxygenic photosynthetic microorganisms represents an intriguing topic in this context, mainly from the point of view of food and O2 production. The aim of the present study was to assess the effects of space ionizing radiation exposure on the photosynthetic activity of various microorganisms. Materials and methods: Ground-based irradiation experiments were performed using fast neutrons and gamma rays on microorganisms maintained at various light conditions. A stratospheric balloon and a European Space Agency (ESA) flight facility were used to deliver organisms to space at the altitude of 38 and 300 km, respectively. During the balloon flight, the fluorescence activity of the organisms was real-time monitored by means of a special biosensor. Results: The quantum yield of Photosystem II (PSII), measured directly in flight, varied among the microorganisms depending on the light conditions. Darkness and irradiation of cells at 120 and 180 μmol m−2 s−1 enhanced the radiation-induced inhibition of photosynthetic activity, while exposure to weaker light irradiance of 20 and 70 μmol m−2 s−1 protected the cells against damage. Cell permanence in space reduced the photosynthetic growth while the oxygen evolution capacity of the cells after the flight was enhanced. Conclusions: A potential role of PSII in capturing and utilizing ionizing radiation energy is postulated.

The effect of ionising radiation on photosynthetic oxygenic microorganisms for survival in space flight revealed by automatic photosystem II-based biosensors

Photosynthetic microorganisms are expected to be useful to maintain an oxygenic atmosphere and to provide biomass for astronauts in the International Space Station as well as in future long-term space flights. However, fluxes of complex ionizing radiation of various intensities and energies make space an extreme environment for the microorganisms, affecting their photosynthetic efficiency. To automatically monitor the photosynthetic Photosystem II (PSII) activity of microorganisms under space conditions an optical biosensor, which utilizes chlorophyll fluorescence as biological transduction system, was built; the PSII activity was monitored by the biosensor during balloon flights at stratospheric altitudes of about 40 km. The effect of space stress on quantum yield of PSII varied among the tested species depending on the growth light conditions at which they were exposed during the flights.

Biodevices for Space Research

This review focuses on the realisation of optical sensors able to monitor the effect of complex space radiation on biological components, based on the biosensor concept. A biosensor is a device that can reveal a biochemical variable using a biological component interfaced with a transducer. It issues an electric signal which is easy to process, depending on the analysed variable. Biosensors are useful to study the effect of stress conditions on living organisms. One of the goals of this research was to develop two types of biosensors able to monitor directly the response of oxygenic photosynthetic organisms to radiation present in space in view of their importance for future space colonization. In ground experiments and in balloon stratosphere flights, the photosynthetic process has been analysed at the level of photosystem II (PSII), the supramolecular pigment-protein complex in the chloroplast which catalyses the light-induced transfer of electrons from water to plastoquinone; PSII splits water into molecular oxygen, protons and electrons, thereby sustaining an aerobic atmosphere on Earth and providing the reducing equivalents necessary to fix carbon dioxide to organic molecules, creating biomass, food and fuel. The results indicated that presence of space radiation in the dark has a synergistic effect on photosystem II activity, suggesting that PSII D1 protein turnover may be involved in resistance to space stress. The resistance of the tested microorganisms to space stress seems to be related to their position on the evolutive scale of photosynthesis. The present studies allow to establish a regular and reliable correlation between measured physical characteristics of space radiation and biological radiation effect.