Abstract EANA2024-60

Cyanobacteria evolved in the Archean when Earth’s atmosphere was anoxic, and were the first organisms to perform oxygenic photosynthesis, causing the Great Oxygenation Event. They have highly plastic and diverse metabolisms, and can be found almost everywhere on Earth, even in hostile habitats: some strains can tolerate extreme environmental conditions, some can fix N2 and some can even grow in atmospheres deprived of O2 and enriched up to 100% of CO2.

We cannot exclude that organisms with such adaptable metabolisms could have evolved in the permissive conditions of early Mars, and that traces, or extant forms, might have been preserved in refuge subsuperficial sites as Mars’ surface became hostile, preserving them from UV radiation and dessication. Indeed, the search for life on Mars will focus on sedimentary rocks, lava tubes, caves and hot springs deposits, considered suitable locations for traces of life or biosignatures preserved in minerals. This investigation will surely benefit from the study of Earth’s organisms living in Mars’ analogues sites.

Interestingly, cyanobacterial communities were found in many analogues of Mars: in desert rocks, in lava caves, and in hot springs. A common feature of these subsuperficial environments is the scarcity of visible (VIS) light and the abundance of Far-Red (FR) and Infrared (IR) light, which poses the question of how can phototrophic organisms like cyanobacteria perform oxygenic photosynthesis, a process driven by VIS-light.

Nonetheless, few cyanobacterial strains, around 1% of known species, were recently found capable of growing relying only on FR-light through an acclimation called Far-Red Light Photoacclimation (FaRLiP). These strains were isolated from soils, rocks, caves, and hot springs where they receive the kind of irradiation mentioned before but, surprisingly, FaRLiP species don’t group in phylogenetic analysis and are distributed in punctiform sites across the globe.

Recent molecular studies on the origin of oxygenic photosynthesis hypothesized that some of the earliest cyanobacteria may have had some capacity to utilize far-red light, , before the diversification of extant cyanobacteria.

This suggests that cyanobacteria could have first appeared in shaded/subsuperficial niches, where they’d have been shielded from the higher UV radiations reaching Earth’s surface at the time.

In our laboratory we expose FaRLiP strains from a variety of environments to FR-enriched spectra, to study their response to limiting conditions of irradiation and atmosphere composition. Obtained data, together with literature, point up the potential of FR-light adapted cyanobacteria in the frame of astrobiological research, for either basic and applicative research.

Here we underline the importance of FaRLiP cyanobacteria in the study of the evolution of life on anoxic Earth when subsurperficial environments offered protection from UV radiation. Moreover, we discuss their potentiality in the look for traces of past or extant life in Mars subsuperficial environments and as powerful support tools for explorative missions in the Solar system.