A Low-Pressure, N2/CO2 Atmosphere Is Suitable for Cyanobacterium-Based Life-Support Systems on Mars

The leading space agencies aim for crewed missions to Mars in the coming decades. Among the associated challenges is the need to provide astronauts with life-support consumables and, for a Mars exploration program to be sustainable, most of those consumables should be generated on site. Research is being done to achieve this using cyanobacteria: fed from Mars's regolith and atmosphere, they would serve as a basis for biological life-support systems that rely on local materials. Efficiency will largely depend on cyanobacteria's behavior under artificial atmospheres: a compromise is needed between conditions that would be desirable from a purely engineering and logistical standpoint (by being close to conditions found on the Martian surface) and conditions that optimize cyanobacterial productivity. To help identify this compromise, we developed a low-pressure photobioreactor, dubbed Atmos, that can provide tightly regulated atmospheric conditions to nine cultivation chambers. We used it to study the effects of a 96% N2, 4% CO2 gas mixture at a total pressure of 100 hPa on Anabaena sp. PCC 7938. We showed that those atmospheric conditions (referred to as MDA-1) can support the vigorous autotrophic, diazotrophic growth of cyanobacteria. We found that MDA-1 did not prevent Anabaena sp. from using an analog of Martian regolith (MGS-1) as a nutrient source. Finally, we demonstrated that cyanobacterial biomass grown under MDA-1 could be used for feeding secondary consumers (here, the heterotrophic bacterium E. coli W). Taken as a whole, our results suggest that a mixture of gases extracted from the Martian atmosphere, brought to approximately one tenth of Earth's pressure at sea level, would be suitable for photobioreactor modules of cyanobacterium-based life-support systems. This finding could greatly enhance the viability of such systems on Mars.

Exploiting a perchlorate-tolerant desert cyanobacterium to support bacterial growth for in situ resource utilization on Mars

The presence of perchlorate in the Martian soil may limit in-situ resource utilization (ISRU) technologies to support human outposts. In order to exploit the desiccation, radiation-tolerant cyanobacterium Chroococcidopsis in Biological Life Support Systems based on ISRU, we investigated the perchlorate tolerance of Chroococcidopsis sp. CCMEE 029 and its derivative CCMEE 029 P-MRS. This strain was obtained from dried cells mixed with Martian regolith simulant and exposed to Mars-like conditions during the BIOMEX space experiment. After a 55-day exposure of up to 200 mM perchlorate ions, a tolerance threshold value of 100 mM perchlorate ions was identified for both Chroococcidopsis strains. After 40-day incubation, a Mars-relevant perchlorate concentration of 2.4 mM perchlorate ions, provided as a 60 and 40% mixture of Mg- and Ca-perchlorate, had no negative effect on the growth rate of the two strains. A proof-of-concept experiment was conducted using Chroococcidopsis lysate in ISRU technologies to feed a heterotrophic bacterium, i.e. an Escherichia coli strain capable of metabolizing sucrose. The sucrose content was fivefold increased in Chroococcidopsis cells through air-drying and the yielded lysate successfully supported the bacterial growth. This suggested that Chroococcidopsis is a suitable candidate for ISRU technologies to support heterotrophic BLSS components in a Mars-relevant perchlorate environment that would prove challenging to many other cyanobacteria, allowing a ‘live off the land’ approach on Mars.

Genome Sequence of the Edible Cyanobacterium Arthrospira sp. PCC 8005

ABSTRACT We determined the genome sequence of Arthrospira sp. PCC 8005, a cyanobacterial strain of great interest to the European Space Agency for its nutritive value and oxygenic properties in the Micro-Ecological Life Support System Alternative (MELiSSA) biological life support system for long-term manned missions into space.