Curtobacterium caseinilyticum sp. nov., Curtobacterium subtropicum sp. nov. and Curtobacterium citri sp. nov., isolated from citrus phyllosphere

Three novel Gram-stain-positive, aerobic and rod-shaped bacterial strains, designated RHCKG28 T , RHCJP20 T and RHCKG23 T , were isolated from phyllosphere of healthy citrus leaves collected from Renhua County in Guangdong Province, PR China. 16S rRNA gene sequences comparison and phylogenetic analyses showed that they all belonged to the genus Curtobacterium , among which strain RHCKG28 T showed the highest similarity to Curtobacterium herbarum NBRC 103064 T (99.3 %), while strains RHCJP20 T and RHCKG23 T showed 99.2 and 99.0 % similarity to Curtobacterium citreum JCM 1345 T , respectively. Phylogenomic analysis showed that the three novel strains were most closely related to C. citreum JCM 1345 T and Curtobacterium albidum JCM 1344 T . The novel strains could be distinguished from their closely related type strains in terms of enzyme activities, substrate assimilation and fatty acid profiles. In addition, the average nucleotide identity and digital DNA–DNA hybridization values between the novel strains and closely related type strains were 84.4‒89.5 % and 24.5‒34.1 %, respectively, which were below the threshold values for species delimitation. They all took anteiso-C 15 : 0 , iso-C 16 : 0 and anteiso-C 17 : 0 as the major fatty acids, menaquinone 9 (MK-9) as the sole predominant respiratory quinone, and ornithine as the principal cell-wall diamino acid. The major polar lipids consisted of phosphatidylglycerol, diphosphatidylglycerol and several unidentified glycolipids. The phenotypic, genotypic and chemotaxonomic data supported that they represent three distinct novel species of the genus Curtobacterium , for which the names Curtobacterium caseinilyticum sp. nov., Curtobacterium subtropicum sp. nov. and Curtobacterium citri sp. nov. are proposed, with RHCKG28 T (=GDMCC 1.2667 T =JCM 34828 T ), RHCJP20 T (=GDMCC 1.2668 T =JCM 34829 T ) and RHCKG23 T (=GDMCC 1.2669 T =JCM 34830 T ) as the type strains, respectively.