Microbial Diversity in Extreme Environments

Abstract

Extreme environments -- geothermal vents, deep-sea hydrothermal systems, hypersaline lakes, cryosphere habitats, and acidic mine drainage -- host microbial communities (Bacteria, Archaea, and microbial Eukarya) uniquely adapted to conditions lethal to most life forms, and represent Earth's final biodiversity frontier where the majority of resident taxa remain undescribed by conventional culture-based microbiology. This study applied amplicon sequencing (16S rRNA gene for Bacteria and Archaea; 18S rRNA for microbial Eukarya) and shotgun metagenomics to 2,840 samples from 42 extreme environment sites across five categories (geothermal springs: 10 sites; hypersaline lakes: 10; deep-sea sediments: 8; cryosphere: 8; acidic mine drainage: 6) in Europe, Iceland, and the Mediterranean basin (2019-2022), characterising microbial alpha diversity (Shannon H', Chao1, Faith's PD), beta diversity (Bray-Curtis dissimilarity, UniFrac distance), and metabolic functional diversity (KEGG pathway richness from metagenomes). Geothermal springs showed the highest Archaeal diversity (Shannon H' = 4.84 +/- 0.48) and lowest bacterial diversity -- consistent with the thermophilic Archaea dominating at temperatures > 60 degrees C. Cryosphere habitats showed the highest psychrophilic bacterial diversity (Chao1 = 2,840 +/- 484 OTUs) and highest functional redundancy. A Microbial Extreme Diversity Index (MEDI) integrating all three domains of life diversity, functional metabolic diversity, and endemicity rate predicted biogeochemical process rates (carbon mineralisation, nitrogen cycling) with r = +0.84 and identified geothermal and hypersaline systems as the most functionally unique and conservation-significant extreme environments.