Characterization of the metabolic properties and ecological functions of Thaumarchaeota in terrestrial environments

Anthropogenic nitrogen inputs have disrupted global cycles, driving environmental issues such as eutrophication and biodiversity loss. Ammonia oxidation, the first step in nitrification, was long attributed to bacteria, but ammonia-oxidizing archaea (AOA) of the Thaumarchaeota phylum are now recognized as key players. This dissertation explores AOA diversity, metabolic properties, and ecological roles in freshwater sediments and plant rhizospheres using molecular and cultivation approaches. Findings reveal AOA dominance in gene abundance but limited autotrophic activity, suggesting alternative strategies such as heterotrophy or mixotrophy. Root enrichment cultures identified distinct clades with varied metabolic potential, highlighting diverse lifestyles and contributions to terrestrial nitrogen cycling.