Terrisphaera alpina gen. nov., sp. nov., a Cellulolytic Planctomycete Representing the First Described Soil-Inhabiting Member of the Class Phycisphaerae

A novel planctomycete, strain T20PH1T, was isolated from alpine meadow soil collected at an altitude of 1800 m in the North Caucasus Mountains, Russia. Phylogenomic analysis placed it within the family Tepidisphaeraceae of the class Phycisphaerae. The closest relatives based on 16S rRNA gene sequence similarity are Fontivita pretiosa B-254T (88.9%), ‘Humisphaera borealis’ M1803T (88.6%), and Tepidisphaera mucosa 2842T (88.4%). Strain T20PH1T is the first soil-derived representative of the class Phycisphaerae. Cells of strain T20PH1T are motile, pink-pigmented cocci reproducing by binary fission. This planctomycete is an obligately aerobic chemoorganotroph with growth optima at 25–30 °C and pH 6.0–7.0. A notable functional trait of strain T20PH1T is its ability to grow on cellulose, including microcrystalline, fibrous and carboxymethyl cellulose, as well as on xylan, starch, lichenan and xanthan. The genome comprised a 5.15 Mb chromosome and a 125 kb plasmid with G + C contents of 65.97 and 66.75%, respectively. Genome analysis identified a GH5_5 subfamily cellulase as the most likely enzyme responsible for cellulose degradation by this planctomycete. Based on phenotypic and phylogenomic evidence, strain T20PH1T (=LMG 34157T = KCTC 102499T) was classified as representing a novel genus and species, Terrisphaera alpina gen. nov., sp. nov.