Glaciers as microbial habitats: current knowledge and implication.

Glaciers, formed from the gradual accumulation of snow, can be continuous records representing past environments and recognized as a time capsule of our planetary evolution. Due to extremely harsh conditions, glacial ice has long been considered an uninhabitable ecosystem for microorganisms to sustain their life. However, recent developments in microbiological analysis techniques revealed the presence of unexpectedly diverse microbial strains. Glacial microorganisms could also provide valuable information, including not only biological diversity and structure but also molecular systematics, metabolic profiles, and evolutionary changes from the past climate and ecosystem. However, there are several obstacles in investigating the glacier environment, such as low regional accessibility, technical difficulties of ice coring, potential contamination during the sampling process, and low microbial biomass. This review aims to summarize recent knowledge on decontamination methods, biomass, diversity based on culture-dependent and -independent methods, application of biological proxies, greenhouse gas production and adaptive strategies in glaciers from various regions and to imply further directions for a comprehensive understanding of habitatility in an icy world including outer of our planet.