Theme: 01. Remediation Technology Innovations

Topic Area: 01b. Bioremediation: Advances in Amendment Formulations

Formatted Title:

Initiating the Biotransformation of Martian Regolith by Dissimilatory Perchlorate-Reducing Microorganisms

Background/Objectives:

Perchlorate (ClO₄^-) is a highly soluble oxyanion of chlorine, both naturally occurring and manufactured. With an EPA maximum contaminant level of 18 µg L-1, ClO₄^- is toxic to humans and a regulated chemical in drinking water. While ClO₄^- is of concern on Earth mainly from anthropogenic activities, ClO₄^-is naturally-occurring and a major component in the regolith (top surface material) on Mars. ClO₄^- was identified by NASA’s Phoenix Mars Lander at 0.5-1 wt% in regolith. As humanity is preparing for a mission to Mars, a major challenge with growing food using Martian regolith is the presence of ClO₄^-. Studies that have been conducted with Martian regolith simulants to test viability for plant growth have concluded that ClO₄^- inhibits plant growth and the regolith material cannot be directly used for food cultivation. On Earth, dissimilatory perchlorate reducing bacteria can use perchlorate as an electron acceptor and have been shown to fully reduce ClO₄^- at concentrations as high as 2.4 g/L. In this project, we are investigating ClO₄^- reduction by pure and mixed cultures to biotransform Martian regolith simulant.

Approach/Activities:

Microcosms with Martian regolith simulant and with either a perchlorate-reducing bacterial mixed culture and an archaon pure culture of Haloferax denitrificans were set up in sealed serum bottles. Concentrations ranging from 1 to 8 g/L ClO₄^- were tested in Martian regolith simulant (commercially available MGS-1 simulant) spiked with 1 wt% ClO₄^-by adding the appropriate amount of water to create unsaturated and saturated regolith conditions. Liquid and gas samples were taken to measure perchlorate, acetate, CO₂, and other metabolites.

Results/Lessons Learned:

Both Haloferax denitrificans and the mixed culture were able to reduce ClO₄^- at concentrations relevant to Martian regolith. At 1 g/L, the mixed culture reduced 75% of the initial perchlorate while the pure culture reduced 31%. At 2.5 g/L the reduction was 45% and 36% for the mixed and pure cultures respectively. At 5 g/L we achieved full reduction with the mixed culture and 49% of perchlorate reduction with the pure culture. Finally, at 8 g/L there was no reduction in the mixed culture condition but 41% of reduction was achieved with Haloferax denitrificans.

In the mixed culture conditions, acetate was completely reduced in all concentrations. In those conditions where perchlorate was not completely reduced, we observed sulfate reduction up to 30% of the initial concentration; which indicates a competition between perchlorate and sulfate.

Research from this project provides insight into ClO₄^- reduction for space exploration but also informs remediation efforts on Earth in soil and groundwater.

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Briana Paiz

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