A new species of Curtobacterium from apple fruit: Curtobacterium pomorum sp. nov. resistant to heavy metals

ABSTRACT The genus Curtobacterium has been frequently found in soil and plants. In this study, we isolated the bacterial strain designated KT1 from an apple fruit. The 16S rRNA gene sequence of the KT1 was identical to those of Curtobacterium flaccumfaciens and Curtobacterium allii type strains. The average nucleotide identities between the complete genomes of the strain KT1 and the two strains were 89.3% and 89.2%, and the digital DNA–DNA hybridization values were 64.2% and 60.5%, respectively, which were less than the threshold values for species delimitation. Phylogenetic analysis based on orthologs of genus Curtobacterium categorized the strain KT1 into a cluster that contained no representative or type strain genome. The strain KT1 grew at a pH range of 5.0–10.0, while C. flaccumfaciens JCM 1347 (=ATCC 6887) grew at pH 5.0–9.0. KT1 cells had abundant anteiso-heptadecanoic acid. The strain KT1 exclusively possessed a gene island containing genes encoding a CueP family metal-binding protein, heavy metal translocating P-type ATPases, and a metal-sensitive transcriptional regulator. Growth of the strain KT1 was significantly more than that of C. flaccumfaciens JCM 1347 at the concentrations of 2 µg/mL cadmium sulfate and 300 µg/mL copper sulfate, indicating that the genomic island is involved in resistance against heavy metals. IMPORTANCE Curtobacterium strain KT1 showed low genome sequence identity with known species in the same genus and met the criteria for classification as a novel species. Further phenotypic and physiological characterization revealed notable differences from related species, including carbon source utilization, optimal growth temperature, pH tolerance, and fatty acid profile. Heavy metal resistance of the strain indicated its ability to grow in cadmium/copper-contaminating soils and host plants. Based on the polyphasic data, we propose that the KT1 T strain (=DSM 118677 T =JCM 37513 T ) is a novel species belonging to the genus Curtobacterium and name it as Curtobacterium pomorum sp. nov.