Tundrisphaera macrotermitis sp. nov., a novel member of the family Isosphaeraceae isolated from the gut of a fungus-growing termite

Abstract

Abstract A pink-pigmented, neutrophilic and mesophilic strain, TA3 T , was isolated from the hindgut of a fungus-growing termite of the species Macrotermes natalensis . Phylogenetic analysis placed the strain in the family Isosphaeraceae , order Isosphaerales , class Planctomycetia , phylum Planctomycetota . The isolate turned out to be an aerobic chemoorganoheterotroph capable of growth under microaerobic conditions. Cells are non-motile, spherical, and either form shapeless aggregates or grow as single cells. The average cell size (length x width) is 2.5 ± 0.3 μm x 2.3 ± 0.2 μm. Cells divide asymmetrically by budding. Optimum pH and temperature for growth are 7.5 (range 6.0–9.0) and 24 °C (range 18–28 °C), respectively. The strain has a genome size of 7.23 Mbp with 69.3% DNA G + C content and it contains four plasmids. Since the genome of the currently known closest relative Tundrisphaera lichenicola has not been sequenced, the previously characterized type strain P12 T was included for genome sequencing. A comparison based on established phylogenetic markers yielded a 16S rRNA gene sequence similarity of 94.8%, an average nucleotide identity of 78.4% and a digital DNA-DNA hybridization (dDDH) value of 20.3%, suggesting a relationship of the two strains on the level of the same genus. Differences in genome-encoded features, e.g. carbohydrate-active enzymes, secondary metabolite-associated biosynthetic gene clusters and plasmid-located genes were analyzed using comparative genomics. Together with whole genome-based phylogenetic analyses and differences in phenotypic characteristics, the data justifies the delineation of the novel isolate from the sole known species in the genus Tundrisphaera . We therefore introduce Tundrisphaera macrotermitis sp. nov. that is represented by TA3 T (= CECT 30560 T  = STH00997 T ) as the type strain.