Why do you want to grow cyanobacteria on Mars?

Establishing a long-term human presence on the red planet requires the ability to produce materials from on-site resources i.e. in-situ resource utilization. The complicating factor is that most industrially-relevant organisms could not be fed with what is found on Mars only. As a solution, cyanobacteria have been proposed as primary producers to feed these bioprocesses as they can grow solely on the limited Martian resources.

How exactly do you grow cyanobacteria on Mars?

The ingredients are: sunlight for energy; carbon and nitrogen from the Martian atmosphere; and Martian soil - regolith - for mineral nutrients. These components combined with adequate environmental conditions allow cyanobacteria to thrive. However, there is a catch. The regolith contains perchlorate, a toxic compound that inhibits growth. It is necessary to find an optimum between providing enough regolith as a nutrient source but not too much of the underlying perchlorate.

What is this research about?

In previous work, we selected Anabaena sp. PCC 7938 as a model cyanobacterium for Mars in-situ resource utilization. Here, we characterized its growth dynamics while relying on regolith as a source of mineral nutrients. Growth was described as a function of the concentration of regolith and perchlorate, independently and combined. The growth dynamics were fitted to mathematical models which allowed us to predict the optimum regolith concentration to supply for growth.

We also evidenced that providing light to cultures which have regolith in suspension would be difficult due to shading. In an attempt to overcome this, we tried separating the cyanobacteria and regolith using a membrane that still permitted ion diffusion. Growth was decreased suggesting that direct contact benefits nutrient extraction.

How do we improve growth on regolith?

In addition to characterizing general growth on regolith, we identified the limiting nutrient. It is phosphorus! Higher biomass production was achieved via phosphorus supplementation. On Mars, exploration efforts can be directed to find phosphorus-rich regolith to feed cyanobacteria and improve their growth.

What is next?

There is still plenty of work ahead to make cyanobacteria bioproduction on Mars a reality. A key point is understanding what are the mechanisms they use to extract nutrients from the regolith. Further research is also necessary to adapt current photobioreactor designs that avoid regolith shading. Stay tuned to find out more!