The discovery on the Martian surface of perchlorate at the levels of 0.4-0.6 wt% has profound implications for the habitability of this planet (Hassler et al. 2013). In order to further investigate the effects of this highly oxidizing agent on microbial survival we exposed a model astrobiological organism, the desiccation-, radiation-tolerant cyanobacterium Chroococcidiopsis sp. CCMEE 029 (Billi 2018), to different perchlorate concentrations. Although this cyanobacterium has been shown to be highly resistant to space and Mars-like conditions (Billi et al. 2019a; Billi et al. 2019b), its capability to cope with perchlorate salts remains unexplored. Therefore in order to investigate the effects of perchlorate on the survival limit and adaptation potential of this extreme-tolerant microorganism, Chroococcidiopsis cells were grown in BG-11 liquid medium supplemented with 5 mM, 50 mM and 100 mM Mg(ClO4-)2, NaClO4- and Ca(ClO4-), as well as with 2.4 mM perchlorate as reported by NASA's lander Phoenix (Hassler et al. 2013). The effects of such a highly oxidizing environment on the cyanobacterial growth and morphology were evaluated by monitoring cell densities over one-month period and by staining treated cells with molecular probes (Billi 2009).

Results revealed that perchlorate concentrations up 50 mM did not alter the growth or the morphology of Chroococcidiopsis sp. CCMEE 029, thus providing relevant information for future experiments under Mars-like conditions to be performed by using ground-based simulations or space facilities either available outside the International Space Station or future ones on the Moon's surface or orbiting around it, e.g. the Gateway.

Furthermore, cell lysates obtained from Chroococcidiopsis cells grown in the presence of 2.4 mM perchlorate were successfully used to support the growth of the heterotrophic bacterium Escherichia coli, thus providing a first milestone in the development of a biological life support system based on in situ resource utilization by means of a cyanobacterium-based technology (Billi et al 2013; Verseux et al. 2016).

Acknowledgements

This research was supported by the Italian Space Agency (grant Life in Space 2019-3-U.0).

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