Astrobiology Revealed #31: Daniela Billi
on the significance of desert cyanobacteria in astrobiology
by Aubrey Zerkle
In this Q&A, we asked Daniela Billi about her recent paper “Desert cyanobacteria under non-Earth conditions: Implications for astrobiology and sustainable life support.” Daniela is a Professor of Food and Agri-environmental Microbiology at the University of Rome “Tor Vergata.” She discusses why desert cyanobacteria in the genus Chroococcidiopsis are model organisms for studying photosynthesis on other planets and shares some of the cool experiments they’ve been involved in. (This interview has been edited for length and clarity.)
How did you become interested in astrobiology in general and in desert cyanobacteria in particular?
I obtained a PhD in Cellular and Molecular Biology, investigating the survival strategies of cyanobacteria isolated from extreme deserts, such as the Dry Valleys of Antarctica, that are considered Mars analogues. These cyanobacteria are part of a culture collection of microorganisms from extreme environments, established by E. Imre Friedmann and Roseli Ocampo-Friedmann. Curiously, at the time I was defending my PhD thesis back in 1996, NASA launched the astrobiology program, with the aim of searching for life in habitable worlds in the Solar system and beyond, as a follow-up of the Exobiology program founded in 1960 to search for life on Mars with the Viking missions.
The event that undoubtedly marked my entire research activity was when Imre and Roseli entrusted me with the maintenance of their collection of cyanobacteria belonging to the Chroococcidiopsis genus, collected over 40 years of expeditions to the most remote deserts on Earth, such as the McMurdo Dry Valleys (Antarctica), the Gobi Desert (Mongolia), the Atacama Desert (Chile), the Negev Desert (Israel), and the Sonora Desert (Mexico).
In your recent review in Acta Astronautica, you argued that these desert cyanobacteria are ideal model organisms to study the potential for extraterrestrial life. Why is that?
Desert cyanobacteria of the genus Chroococcidiopsis are unique organisms for astrobiology experiments thanks to their extreme desiccation- and radiation- tolerance. Our knowledge of the tenacity of life that guides its search elsewhere has been expanded by the survival of these cyanobacteria in the air-dried state when exposed for 1.5 years to space and Mars-like conditions onboard the EXPOSE facility installed outside the International Space Station, and during the BIOMEX (BIOlogy and Mars EXperiment) and BOSS (Biofilm Organisms Surfing Space) projects.
In fact, upon retrieval back to Earth and rehydration, the cyanobacteria exposed to non-Earth conditions repaired the damage they had accumulated while in space. These results also provide an important requisite for new experiments in more hostile environments beyond low Earth orbit, such as deep space or the Moon's surface, where they will hopefully be exposed in a hydrated, metabolically active state.
You also mentioned that these microbes perform oxygenic photosynthesis using infrared light. What is the significance of this process in astrobiology?
Notably, a few isolates among desert strains of Chroococcidiopsis can modify their photosynthetic apparatus to use light beyond the visible. This capability has important implications for the possibility of life on planets orbiting M-stars with infrared-shifted emission spectra, because oxygen and ozone [products of photosynthesis] remain the leading options for detecting biosignatures.
In your paper, you discuss all the space experiments these microbes have been (or will be) included in. What's the most surprising thing you've learned from these experiments so far?
The most surprising thing is that they always survived the multiple stressful conditions they have been exposed to [including sub-freezing temperatures, extreme desiccation, Mars-like UV fluxes, and high levels of ionizing radiation]. This makes them a perfect candidate to explore the limits of life as we know it and to maybe even exceed it through a synthetic biology approach.
Which of the planned or upcoming experiments are you most excited about?
I am looking forward to participating in the maiden flight of the ESA Space Rider, scheduled for 2028, with the CyanoTechRider experiment. It will investigate the effects of microgravity and space radiation on the efficiency of Chroococcidiopsis’s DNA repair. This should contribute to its use as a chassis in space biotechnology applications, to support human outposts on the Moon or Mars.
How might these organisms contribute to life-support technologies, for example, on a human mission to Mars?
Desert cyanobacteria of the Chroococcidiopsis genus are particularly interesting for the development of technologies to support human space exploration, thanks to their ability to produce oxygen [which we breathe] and fix carbon [which we eat] through oxygenic photosynthesis. They also have the capability of utilizing urine [our waste product] as a nitrogen source and minerals from simulants of the Martian and lunar soil.
Want to know more? See Daniela’s TEDx talk “Green bacteria between Earth and Mars”!