Investigation of Thaumarchaeal diverity in the hypoxic-anoxic zones of the southern Ocean.. Thaumarchaeal diversity in the ETSP

Limited information exists on the time and space variability of the dominant and “rare” nitrifying Thaumarchaeal populations in marine environments. To evaluate shifts in the diversity of Thaumarchaeal ammonia oxidizers, the ammonia monooxygenase subunit A (amoA) gene was deep sequenced from samples collected monthly at a time-series station over the continental shelf off central Chile (36.5 °S) over one year. Temperature, salinity, and depth displayed a stronger impact on community composition than chemical (dissolved oxygen, nitrogen) and biological variables (pico-eukaryotes, Synecococcus). The Nitrosopumilus water-column A clade displayed high proportional representation in all samples. However, different representative operational taxonomic units within this clade displayed significant differences in their relative abundances that were highly correlated with depth, indicating that depth-dependent shifts occur within this clade that have not been previously observed. Nitrosopumilus water-column B representatives displayed increased proportional abundances in water samples collected at deeper depths amid stratified conditions in the austral summer. Low abundance Nitrosopumilus and Nitrosotalea clades were observed, and were sometimes associated with specific spatial or seasonal attributes of the water column. The data highlight a strong coupling between community diversity and physical oceanographic variables, and highlight the utility of deep sequencing for identifying low abundance, or ‘rare’ thaumarcheota.