Knoellia altitudinis sp. nov., Knoellia pratensis sp. nov., Knoellia terrae sp. nov. and Knoellia tibetensis sp. nov., four novel UV radiation-resistant actinobacteria isolated from Tibet Autonomous Region, China

Four Gram-stain-positive, aerobic, non-motile and non-spore-forming actinobacterial strains (CPCC 206391^T, CPCC 206453^T, CPCC 206435^T and CPCC 206450^T) were isolated from soil samples collected from Tibet Autonomous Region, China. The 16S rRNA gene sequences of these four strains showed close relations to members of the genus <i>Knoellia</i> of the family <i>Intrasporangiaceae</i>, with similarities of 96.1-99.4% to the validly named species of <i>Knoellia</i>. In the phylogenetic trees based on 16S rRNA gene sequences and the core genome, these isolates clustered into the genus <i>Knoellia</i> clade within the lineage of the family <i>Intrasporangiaceae</i>. Genome relatedness index values between these strains and their phylogenetic neighbours, including average nucleotide identity (78.1-91.5%) and digital DNA-DNA hybridization (19.8-41.0%), were all below the species delineation thresholds. These genomic data, combined with their phenotypic characteristics, supported their classification within the genus <i>Knoellia</i>, representing four novel species. Thereby, <i>Knoellia altitudinis</i> sp. nov. (type strain CPCC 206391^T=XZ253^T=KCTC 59139^T), <i>Knoellia pratensis</i> sp. nov. (type strain CPCC 206453^T=CXZ644^T=KCTC 59274^T), <i>Knoellia terrae</i> sp. nov. (type strain CPCC 206435^T=CXZ904^T=KCTC 59271^T) and <i>Knoellia tibetensis</i> sp. nov. (type strain CPCC 206450^T=XZ100^T=KCTC 59273^T) were proposed. These strains exhibited stable growth under high-intensity UV radiation, attributed to the presence of <i>uvrABC</i> and <i>recAFNOQR</i> genes involved in UV resistance and DNA repair. These features indicate the <i>Knoellia</i> spp<i>.</i> adaptation to high UV radiation environments.