Existence and distribution of novel phylotypes of Nitrospira in water columnsof the South China Sea

In the biological nitrogen cycle, nitrite oxidation is performed by nitrite oxidation bacteria, of which Nitrospira is widespread and diverse. Communities of Nitrospira were collected at 25–1500 m depths in the South China Sea. Phylogenetic diversity, community composition, and environmental factors were investigated using high-throughput sequencing targeting the nxrB gene and statistical analyses. The community composition of Nitrospira varied spatially and by depth. Among the 24 OTUs with relatively high abundance, 70% were unclassified and not affiliated with the known Nitrospira genus, suggesting a previously unrecognized high diversity of marine Nitrospira. Five known Nitrospira genera were detected, of which the common marine Nitrospira marina was not the dominant species, whereas Candidatus Nitrospira lenta and Candidatus Nitrospira defluvii dominated in shallow habitats. Comammox Candidatus Nitrospira nitrosa was discovered in the marine ecosystem. The niche differentiation of versatile Nitrospira species was mainly shaped by nitrate, temperature, and DO.