Abstract_EANA2026-45

Abstract EANA2026-45

From Molecular Asymmetry to Microbial Biosignatures: Detecting Homochirality and Biological Pigments through Spectropolarimetry

Lisa Brandenburg (1,2), Mathilda Fatton (1,2), Jonathan Grone (1), Lucas Patty (1,3), Urs Schroffenegger (1), Pilar Junier (2), Brice-Olivier Demory (1,3)

(1) Center for Space and Habitability, University of Bern, Switzerland (2) Laboratory of Microbiology University of Neuchatel, Switzerland (3) ARTORG Center for Biomedical Engineering Research, University of Bern, Switzerland

The search for life beyond Earth increasingly relies on biosignatures that can be detected remotely and distinguished from abiotic false positives. Biological homochirality is particularly compelling in this context because it is universal across all known life and intrinsically linked to molecular self-organization. In photosynthetic organisms, homochirality is expressed in pigment-protein complexes that generate characteristic circular polarisation (CP) signatures. Spectropolarimetry (measuring CP) can therefore connect the detection of biological pigments with the detection of homochiral organization, offering a more robust framework for identifying photosynthetic life remotely.

Within the SenseLife project, we develop the Full-Stokes spectropolarimeter FlyPol to investigate CP signatures from a broad diversity of microorganisms relevant to astrobiology. FlyPol measures wavelength-dependent circular polarization with high sensitivity in the visible spectral range, targeting biological pigments absorbing between approximately 500 and 800 nm. Because photosynthetic pigments are embedded within homochiral pigment-protein complexes, their optical activity produces characteristic CP spectral features that can serve as remotely detectable biosignatures.

To characterize the diversity and robustness of these signatures, we measured CP spectra from multiple microbial strains spanning distinct evolutionary and metabolic groups, including oxygenic cyanobacteria, anoxygenic phototrophic bacteria, algae, and extremophilic microorganisms containing alternative pigments. Across all investigated taxa, we detected reproducible CP signatures associated with major biological pigments such as chlorophyll a, phycocyanin, phycoerythrin, carotenoids, and bacteriochlorophylls. Oxygenic phototrophs displayed characteristic split CP signals near chlorophyll absorption bands, whereas anoxygenic phototrophs exhibited distinct spectral features linked to bacteriochlorophyll-containing photosystems. These differences suggest that spectropolarimetry may distinguish between fundamentally different photosynthetic metabolisms remotely.

In addition to qualitative biosignature detection, we investigated the quantitative relationship between CP signal strength and microbial physiology. Time-course growth experiments combined spectropolarimetric measurements with flow cytometry and spectrophotometric pigment analyses to assess the influence of both cell density and intracellular pigment concentration on CP amplitude. Our results demonstrate that CP intensity scales not only with biomass but also with pigment concentration per cell, establishing circular polarization as a biologically meaningful parameter reflecting cellular pigment architecture and organization.

By combining the detection of homochirality with pigment-specific spectral information, spectropolarimetry provides an integrated framework for biosignature detection that is less susceptible to abiotic false positives than conventional spectroscopy alone. These findings support the potential of circular spectropolarimetry as a future remote-sensing technique for detecting microbial life on planetary surfaces and exoplanets.