Microbes inhabit almost every niche on our planet, including extreme environments where microbial life persists despite significant environmental stressors such as extreme temperatures, desiccation, UV radiation, and carbon and nutrient starvation. Despite these challenging conditions, such environments host surprisingly diverse and abundant microbial communities whose metabolic flexibility enables them to persist under energy-limited conditions. Studying the taxonomic composition and functional capabilities of these communities through the use of metagenomics enables insights into previously uncultured or unknown organisms and the metabolic pathways they may use to harvest energy and nutrients from various sources. Metagenomics is especially powerful when combined with biogeochemical measurements to examine community activities and dynamics. Demonstrating the strengths of combining these approaches, this talk will showcase recent advances on the microbial consumption of atmospheric trace gases: a significant, but until recently, overlooked source of energy and carbon for microbes in a range of ecosystems including arid desert soils and cold oligotrophic marine waters.