Membrane-Spanning Molecular Lengths as an Agnostic Biosignature

Area of Science:

• Astrobiology
• Biochemistry
• Organic Chemistry

Background:

• Cell membranes are essential for life, composed of lipid-like molecules with specific functional requirements.
• Membrane thickness is a critical parameter, likely conserved across different molecular classes within an organism due to interdependent molecular structures.
• Identifying conserved molecular properties could serve as a universal biosignature for extraterrestrial life.

Purpose of the Study:

• To test the hypothesis that similar abundance-averaged lengths of lipid-like molecules indicate a conserved membrane thickness, serving as a biosignature.
• To develop and validate a method for estimating membrane thickness from modeled lengths of various membrane-forming molecules.
• To assess the potential of this approach as an agnostic biosignature for detecting life on other worlds.

Main Methods:

• Developed a method to model the lengths of lipid-like molecules and estimate the resulting membrane thicknesses.
• Analyzed abundance patterns of four key terrestrial membrane molecule classes: fatty acids, glycerol dialkyl glycerol tetraethers, carotenoids, and ladderanes.
• Included microbial isolates, environmental samples, and abiotic fatty acid samples for comparison.

Main Results:

• Modeled cell membrane thicknesses derived from different molecular classes showed remarkable similarity.
• Estimated thicknesses were consistent with observed values for terrestrial biological membranes.
• Abiotic fatty acid samples did not yield similar thickness estimations, supporting the biological origin hypothesis.

Conclusions:

• The conserved membrane thickness across diverse molecular classes supports the hypothesis and suggests a viable biosignature.
• The developed method provides a robust framework for identifying potential membrane components as agnostic biosignatures.
• Comparing multiple molecular classes enhances confidence in biological detection, crucial for astrobiological exploration.