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.

Abstract

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 Knoellia of the family Intrasporangiaceae, with similarities of 96.1-99.4% to the validly named species of Knoellia. In the phylogenetic trees based on 16S rRNA gene sequences and the core genome, these isolates clustered into the genus Knoellia clade within the lineage of the family Intrasporangiaceae. 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 Knoellia, representing four novel species. Thereby, Knoellia altitudinis sp. nov. (type strain CPCC 206391^T=XZ253^T=KCTC 59139^T), Knoellia pratensis sp. nov. (type strain CPCC 206453^T=CXZ644^T=KCTC 59274^T), Knoellia terrae sp. nov. (type strain CPCC 206435^T=CXZ904^T=KCTC 59271^T) and Knoellia tibetensis 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 uvrABC and recAFNOQR genes involved in UV resistance and DNA repair. These features indicate the Knoellia spp. adaptation to high UV radiation environments.