Comparing Protein Stability in Modern and Ancient Sabkha Environments: Implications for Molecular Remnants on Ancient Mars.

Understanding the mechanisms of protein preservation in extreme environments is essential for identifying potential molecular biosignatures on Mars. In this study, we investigated five sabkha sedimentary samples from the Abu Dhabi coast, spanning from the present day to ~11,000 years before present (BP), to assess how mineralogy and environmental conditions influence long-term protein stability. Using LC-MS/MS and direct Data-independent Acquisition (DIA) proteomic analysis, we identified 722 protein groups and 1300 peptides, revealing a strong correlation between preservation and matrix composition. Carbonate- and silica-rich samples favored the retention of DNA-binding and metal-coordinating proteins via mineral-protein interactions, while halite- and gypsum-dominated facies showed lower recovery due to extreme salinity and reduced biomass input. Functional profiling revealed a shift from metabolic dominance in modern samples to genome maintenance strategies in ancient ones, indicating microbial adaptation to prolonged environmental stress. Contrary to expectations, some ancient samples preserved large, multi-domain proteins, suggesting that early mineral encapsulation can stabilize structurally complex biomolecules over millennial timescales. Taxonomic reconstruction based on preserved proteins showed broad archaeal diversity, including Thaumarchaeota and thermophilic lineages, expanding our understanding of microbial ecology in hypersaline systems. These findings highlight sabkhas as valuable analogs for Martian evaporitic environments and suggest that carbonate-silica matrices on Mars may offer optimal conditions for preserving ancient molecular traces of life.