Cultivation-Based Detection of a Novel High-GC Nitrospira Derived From the Argentinian Copahue Volcano Area

Nitrification is an essential process within the global nitrogen cycle and also occurs under extreme conditions, such as in geothermal environments. The nitrite-oxidizing group Nitrospira represents key nitrifiers in these systems, as several species inhabit hot springs worldwide. Using different initial incubation temperatures, two novel moderately thermophilic Nitrospira enrichments, Nitrospira sp. Vd2 and Ca. N. neuquenensis E2OT, were obtained from sulfur-rich mud pools in the geothermal field Las Máquinas (Neuquén Province, Argentina). Nitrospira sp. Vd2 belongs to the N. bockiana lineage V, whereas the second enrichment (E2OT) represents the novel taxonomic lineage VIII, together with cultures from Kamchatka (Kam-Ns4a) and Garga hot springs (Ga3a). The vibrioid morphology of Ca. N. neuquenensis E2OT is strikingly different from all described, twisted rod-shaped Nitrospira. Our study expands the knowledge of the taxonomic and genomic diversity of moderately thermophilic Nitrospira, by comparing the high-quality draft genomes with those of previously described species. The recent discovery of quorum-sensing genes outside the Nitrospira lineage II was confirmed for both Argentinian cultures. Notably, the genome GC contents of the enrichments Vd2 and E2OT are 60.6% and 69.4%, respectively. The latter is the highest observed for Nitrospira to date and might support thermotolerance up to 50°C.