A new symbiotic nanoarchaeote (Candidatus Nanoclepta minutus) and its host (Zestosphaera tikiterensis gen. nov., sp. nov.) from a New Zealand hot spring

Three thermophilic Nanoarchaeota-Crenarchaeota symbiotic systems have been described. We obtained another stable anaerobic enrichment culture at 80 degrees C, pH 6.0 from a New Zealand hot spring. The nanoarchaeote (Ncl-1) and its host (NZ3(T)) were isolated in co-culture and their genomes assembled. The small (similar to 200 nm) flagellated cocci were often attached to larger cocci. Based on 16S rRNA gene similarity (88.4%) and average amino acid identity (52%), Ncl-1 is closely related to Candidatus Nanopusillus acidilobi. Their genomes both encode for archaeal flagella and partial glycolysis and gluconeogenesis pathways, but lack ATP synthase genes. Like Nanoarchaeum equitans, Ncl-1 has a CRISPR-Cas system. Ncl-1 also relies on its crenarchaeotal host for most of its biosynthetic needs. The host NZ3(T) was isolated and grows on proteinaceous substrates but not on sugars, alcohols, or fatty acids. NZ3(T) requires thiosulfate and grows best at 82 degrees C, pH 6.0. NZ3(T) is most closely related to the Desulfurococcaceae, Ignisphaera aggregans (similar to 92% 16S rRNA gene sequence similarity, 45% AAI). Based on phylogenetic, physiological and genomic data, Ncl-1 and NZ3(T) represent novel genera in the Nanoarchaeota and the Desulfurococcaceae, respectively, with the proposed names Candidatus Nanoclepta minutus and Zestosphaera tikiterensis gen. nov., sp. nov., type strain NZ3(T) (=DSMZ 107634(T) = OCM 1213(T)). (C) 2018 Elsevier GmbH. All rights reserved.