Molecular Insights into Heat-Inducible HSP70s from Psychrophilic Bacteria and Yeast as Indicators of Ecosystem Stress in Antarctica

Rapid warming in Antarctica is reshaping microbial habitats, yet sensitive molecular indicators of thermal stress remain limited. Heat shock protein 70 (HSP70), a conserved molecular chaperone, is a promising ecological biomarker due to its sensitivity to stress conditions, but isoform-specific functions in Antarctic psychrophiles remain poorly resolved. In this study, we characterised eight HSP70 isoforms from the yeast Glaciozyma antarctica PI12 and the bacterium Pedobacter cryoconitis BG5 through integrated structural modeling, recombinant protein assays and gene expression profiling. All isoforms exhibited optimal ATPase activity at 15°C, confirming cold-adapted function. Notably, the isoforms displayed specialized functions, with high ATPase activity at 15°C observed for gaHSP70-5, gaHSP70-6, and pcHSP70-1, and effective chaperone activity against heat-induced aggregation at 43°C exhibited by pcHSP70-2, gaHSP70-4 and gaHSP70-6. Gene expression analysis revealed that gahsp70-1 , gahsp70-2 , gahsp70-3 and pchsp70-1 were upregulated at higher temperatures, whereas gahsp70-5 and gahsp70-6 were significantly upregulated in response to cold stress. Structural analysis revealed cold-adaptive traits, such as increased flexibility, the absence of disulfide bridges, and fewer aromatic clusters. These features enhance their stability and function in extreme environments. Among all, pchsp70-1 and gahsp70-3 emerged as the optimal biomarkers, with gahsp70-3 displaying heightened inducibility during repeated heat exposure. This research highlights the functional divergence among Antarctic HSP70s and provides isoform-specific biomarkers with strong potential for monitoring climate-driven stress in polar ecosystems.