Kueselia aquadivae gen. nov., sp. nov., the first member of the family Isosphaeraceae isolated from subsurface percolates.

Subsurface habitats, found under various geological conditions, exhibit diverse microbial communities. The vadose zone, a previously unexplored subsurface compartment, connects the surface to phreatic groundwater. Drilling into the subsurface allows access to these habitats for microbial diversity study. Due to nutrient limitation, subsurface microbiomes adapt, potentially producing biotechnologically important biomolecules. Planctomycetota, known for possessing about 20 to 45% of protein-coding genes of unknown function, may be relevant in this context. A percolate water sample from the weathered bedrock of the Hainich Critical Zone Exploratory (CZE; Thuringia, Germany) was processed to enrich planctomycetes, leading to the isolation of an uncharacterized Isosphaeraceae member, strain EP7T. Strain EP7T forms round, pink colonies, and spherical, non-motile cells that divide asymmetrically by budding. It grows between 10 and 24 °C and over a range of pH 5 to pH 10. Its genome size is 7.2 Mbp, and its DNA G + C content is 66.7%. Polyphasic characterization justifies the assignment of strain EP7T to a novel species within a novel genus. We introduce the name Kueselia aquadivae for the novel taxon with strain EP7T as the type strain of the novel species. Strain EP7T represents the first Isosphaeraceae member isolated from vadose zone percolate water.