Extant life detection using label-free video microscopy in analog aquatic environments

Area of Science:

• Astrobiology
• Microbiology
• Geochemistry

Background:

• Microbial life detection in extreme environments is crucial for astrobiology.
• In situ characterization of microbial biosignatures is challenging.
• Previous imaging efforts have not explored diverse extreme field sites.

Purpose of the Study:

• Investigate microbial active motion, morphology, and optical properties as biosignatures.
• Assess the utility of in situ video microscopy for life detection in extreme environments.
• Evaluate methods for stimulating microbial activity and processing data for space missions.

Main Methods:

• In situ video microscopy was employed across diverse extreme field sites.
• Samples included seawater, sea ice brines, cryopeg brines, hypersaline pools, hyperalkaline springs, and cave ice.
• An autonomous, open-source software package was used for data classification.

Main Results:

• Active microbial motion was observed in most samples without treatment, and in cryopeg brines with a temperature gradient.
• Motility increased significantly with stimuli like warming and L-serine addition; chemotaxis and thermotaxis were observed.
• Non-motile cells were distinguishable from minerals by passive motion, optical properties, and morphology.

Conclusions:

• Volumetric light microscopy is a valuable tool for in situ life detection.
• Stimulating cells in situ and developing space-mission-compatible data processing are important.
• Future missions require instruments for capturing cell-like objects for chemical analysis.