Aquirufa lenticrescens sp. nov. and Aquirufa aurantiipilula sp. nov.: two new species of a lineage of widespread freshwater bacteria

Two bacterial strains, 9H-EGSE(T) and 15D-MOB(T), were isolated from small freshwater habitats located near Salzburg, Austria. They showed the highest 16S rRNA sequence similarities of 100% and 99.9%, respectively, with type strains of species of the genus Aquirufa (Bacteroidota). Genome-based phylogenetic reconstructions with 119 amino acid sequences assigned the new taxa to the two distinct branches of the genus Aquirufa. Whole-genome average nucleotide identities were calculated with all possible pairs belonging to the genus. Values between 75.4% and 88.6% revealed that the two new strains represent each a new species. Like all, so far described members of the genus, they grew aerobically and chemoorganotrophically, were rod-shaped, red-pigmented, and motile by gliding, and showed genome sizes of about 3 Mbp and G + C values of about 40%. They could be distinguished by some phenotypic and chemotaxonomic features from their nearest related species. Until now, strain 9H-EGSE(T) is the only one among the Aquirufa strains which contained traces of MK8 as respiratory quinone, and strain 15D-MOB(T) is the only one that formed tiny orange globules in liquid medium. The genome of strain 9H-EGSE(T) comprised genes for the complete light-harvesting rhodopsin / retinal system, in the case of 15D-MOB(T) genes predicted for a nitrous oxide reductase were present. For the two new species of the genus Aquirufa, we propose to establish the names Aquirufa lenticrescens for strain 9H-EGSE(T) (= JCM 34077( T) = CIP 111926( T)) and Aquirufa aurantiipilula for strain 15D-MOB(T) (= JCM 34078( T) = CIP 111925( T)). SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00203-022-02950-6.