Enrichment and Genome Sequence of the Group I.1a Ammonia-Oxidizing Archaeon “Ca. Nitrosoterreus chungbukensis” Representing a Clade Globally Distributed in Deep Oligotrophic Soil Horizon

Abstract

The first step of nitrification, i.e., the oxidation of ammonia, was long considered to be performed exclusively by ammonia-oxidizing bacteria (AOB). However, the theory of soil and marine nitrification changed significantly after the discovery of AOA. This study reports the discovery of a chemolithoautotrophic ammonia oxidizer that belongs to a distinct clade of non-marine thaumarchaeal group I.1a, which is widespread in terrestrial environments. Extensive growth assays showed that strain MY2 is chemolithoautotrophic, mesophilic (optimum temperature 30°C), and neutrophilic (optimum pH 7 to 7.5). The genome size of strain MY2 was 1.76 Mb, similar to that of N. maritimus and “Ca. N. koreensis”, and the repertoire of genes required for ammonia oxidation and carbon fixation in thaumarchaeal group I.1a was conserved. High representation of conserved orthologuous genes of signal transduction and motility in the non-core genome might be implicated in niche adaptation by strain MY2. On the basis of phenotypic, phylogenetic, and genomics characteristics, we propose the name “Candidatus Nitrosoterreus chungbukensis” for the ammonia-oxidizing archaeal strain MY2.