Abstract
Microorganisms are essential players in Earth's ecosystems, demonstrating remarkable adaptability to harsh conditions including arctic ice caps, deep-sea hydrothermal vents, and high-pressure oceanic zones. While the study of these extremophiles has long been constrained by challenges in culturing, recent advances in metagenomic techniques have enabled a deeper understanding of microbial diversity in these extreme habitats. This review explores both culturable and non-culturable microbial communities, focusing on the diverse strategies employed by microorganisms to thrive in harsh conditions, including high pressure, temperature, salinity, and nutrient limitations. Traditional cultivation methods often fail to capture the full spectrum of deep-sea microbiota due to the unique growth requirements of many organisms. In the omic era, however, microbial cultivation and the function of microbial resources are important. Non-culturable methods, like metagenomic studies and environmental DNA sequencing, have uncovered hitherto unknown microbial taxa and metabolic pathways, offering important new information on microbial ecology and biogeochemistry. The complex microbial interactions and adaptive methods that support these ecosystems are highlighted by case studies, including as studies on hydrothermal plumes and hadal deposits. The expanding significance of non-culturable techniques in microbial research is highlighted in this review, which also highlights how they might help us better understand microbial life in harsh conditions and how they may be used in biotechnology and environmental management.