Thaumarchaeota

Thaumarchaeota is a phylum of archaea that includes many ammonia-oxidizing organisms. It was proposed in 2008 to accommodate ammonia-oxidizing archaea previously grouped with Crenarchaeota. Members are globally distributed, with representatives in oceans, soils, freshwater, and sediments. They are predominantly chemolithoautotrophs, gaining energy by oxidizing ammonia to nitrite and fixing CO2 as a carbon source, thereby contributing to the first step of nitrification in many ecosystems.

Key metabolic features center on ammonia oxidation mediated by ammonia monooxygenase, encoded by amoA. Thaumarchaeota commonly fix carbon via the 3-hydroxypropionate/4-hydroxybutyrate cycle. Some lineages possess urease, enabling utilization of urea as a nitrogen source. While most members are autotrophs, metabolic capabilities can vary, and mixotrophy has been observed in some strains.

Ecologically, Thaumarchaeota are among the most abundant Archaea in many environments, especially in marine surface waters and soils. They are major contributors to marine nitrification and influence nitrogen availability in soils and sediments. Some lineages tolerate low nutrient or low-oxygen conditions, and thermophilic members are known from hot springs.

Notable representatives include marine Nitrosopumilus species and soil-associated Nitrososphaera, which oxidize ammonia under diverse conditions. The phylum name derives from thaum- meaning wonder, reflecting the unexpected metabolic traits of these organisms.

Research on Thaumarchaeota relies on genomics, metagenomics, and single-cell approaches to reveal diversity, metabolism, and ecological roles. Their discovery reshaped understanding of the global nitrogen cycle by highlighting archaeal ammonia oxidation as a widespread and important process.