Exploring Oxygenic Photosynthesis under Far-Red Light Enriched Spectra: Astro-Biotechnological Relapses

Oxygenic photosynthesis is a highly conserved process producing carbohydrates from CO2 and H2O that was believed to rely on the energy of only visible (VIS) light: photons from 400 to 700 nm. Recently the role of wavelengths beyond 700 nm was rediscovered as far red (FR) photons, up to 750 nm, were found to have a synergistic effect when given together with VIS photons, boosting photosynthetic efficiency. Moreover, some cyanobacteria can grow with FR light solely by synthetizing new pigments harvesting long wavelengths (chlorophyll d and f) and some microalgae can remodel their light harvesting antennae and increase their absorption capacity in the FR. The aim of this thesis was to explore the features and limits of oxygenic photosynthesis in FR light and FR-enriched spectra for both biotechnological and astrobiological research. We evaluated growth and performance of different oxygenic phototrophs – cyanobacteria, microalgae, and plants – in FR or FR-enriched light, investigating and characterizing their acclimation responses. For biotechnological purposes, the obtained results show that organisms growing in FR and/or FR-enriched spectra are a powerful tool as they can uptake CO2 and supply biomass, O2 and biocompounds, with a lower energetic requirement than organisms grown in bright VIS light. This has useful applications for agriculture on Earth but is also interesting in the frame of sustaining human activities in future space missions. For astrobiological research, oxygenic photosynthesis in FR light discloses the possibility of life to have evolved outside the solar system: most planets that have been found as potentially habitable orbit M-dwarf stars and these stars have irradiation spectra poor in VIS light and enriched in FR light, which could be a challenge for the evolution of photosynthesis. We experimentally evaluated the potential of organisms, capable and uncapable of photosynthesizing in FR light, in simulated planetary conditions – stellar irradiation and anoxic atmosphere enriched in CO2. Results demonstrate that the simulated spectrum of an M-dwarf can indeed sustain oxygenic photosynthesis and that organisms display a noticeable biodiversity of responses to the simulated conditions. The data obtained are moreover crucial for climate modeling of exoplanets and as references to the data that will be gathered by planned space missions.