Microbial preference for chlorate over perchlorate under simulated shallow subsurface Mars-like conditions

Area of Science:

• Astrobiology
• Microbiology
• Planetary Science

Background:

• The Martian environment presents challenges for life due to water scarcity and harsh conditions.
• Hygroscopic salts in Martian regolith may facilitate transient liquid brines, potentially supporting microbial life.
• Understanding microbial survival under simulated Martian conditions is crucial for assessing habitability.

Purpose of the Study:

• To investigate the impact of water scarcity, UV radiation, and regolith depth on microbial survival.
• To compare the effects of chlorate and perchlorate salts on microbial survival under simulated Martian conditions.
• To determine the role of regolith depth in mitigating the toxicity of Martian salts.

Main Methods:

• Exposure of *Debaryomyces hansenii*, *Planococcus halocryophilus*, and *Aspergillus niger* spores to simulated Martian conditions (low temperature, low pressure, CO2 atmosphere, UV irradiation).
• Assessment of microbial survival (colony-forming units) and water content at varying regolith depths (3 and 7 days).
• Testing under salt-free, sodium chlorate, and sodium perchlorate conditions.

Main Results:

• Residual water content and microbial survival increased with regolith depth.
• Higher survival rates were observed in salt-free and chlorate-containing regolith compared to perchlorate-containing regolith.
• Perchlorate brines were found to be more toxic than chlorate brines, especially at greater depths with higher water content.

Conclusions:

• Regolith depth and the type of salt significantly influence microbial survival under Martian conditions.
• Chlorate salts appear more conducive to microbial survival than perchlorate salts on Mars.
• These findings highlight the importance of considering specific salt chemistries when evaluating Martian habitability.