Resilience of Metabolically Active Biofilms of a Desert Cyanobacterium Capable of Far-Red Photosynthesis Under Mars-like Conditions

Kurzfassung

The response of the desert cyanobacterium Chroococcidiopsis sp. CCMEE 010 wastested in Mars simulations to investigate the possibility of photosynthesis in near-surfaceprotected niches. This cyanobacterium colonizes lithic niches enriched in far-red light(FRL) and depleted in visible light (VL) and is capable of far-red light photoacclimation(FaRLiP). Biofilms were grown under FRL and VL and exposed in a hydrated state to a lowpressure atmosphere, variable humidity, and UV irradiation, as occur on the Martian surface.VL biofilms showed a maximum quantum efficiency that dropped after 1 h, whereas aslow reduction occurred in FRL biofilms up to undetectable after 8 h, indicating that UVirradiation was the primary cause of photoinhibition. Post-exposure analyses showed thatVL and FRL biofilms were dehydrated, suggesting that they entered a dried, dormantstate and that top-layer cells shielded bottom-layer cells from UV radiation. After Marssimulations, the survivors (12% in VL biofilms and few cells in FRL biofilms) suggested that,during the evolution of Mars habitability, near-surface niches could have been colonizedby phototrophs utilizing low-energy light. The biofilm UV resistance suggests that, duringthe loss of surface habitability on Mars, microbial life-forms might have survived surfaceconditions by taking refuge in near-surface protected niches.