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

Abstract

A pink-pigmented, neutrophilic and mesophilic strain, TA3T, 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 P12T 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 TA3T (= CECT 30560T = STH00997T) as the type strain.