Candidatus Nitrosotalea

Since the late nineteenth century, aerobic ammonia-oxidizing bacteria belonging to the Proteobacteria have been cultivated from a wide range of environments. In the past decade, ammonia-oxidizing archaea belonging to the phylum Thaumarchaeota have also been recognized as an abundant group of organisms that contribute to ammonia oxidation in the majority of terrestrial and aquatic habitats investigated. One lineage within the Thaumarchaeota, currently represented by the cultivated isolates “Candidatus Nitrosotalea devanaterra” and “Candidatus Nitrosotalea sp. Nd2,” is abundant in acidic soil environments. Both isolates are obligate acidophiles, growing optimally around pH 5.0. These organisms are the first and only cultivated autotrophic ammonia oxidizers that do not grow at neutral pH. They possess ≤90% 16S rRNA gene identity with other cultivated thaumarchaea in genera such as Ca. Nitrosopumilus, Nitrososphaera and Ca. Nitrosocaldus, and Ca. Nitrosotalea isolates are therefore representatives of a novel genus within the Thaumarchaeota. Ca. Nitrosotalea are small, rod-shaped cells with angular and electron dense poles. They are obligately aerobic autotrophs and require ammonia as their sole energy source.