Description of Clavibacter zhangzhiyongii sp. nov., a phytopathogenic actinobacterium isolated from barley seeds, causing leaf brown spot and decline.

Abstract

Clavibacter michiganensis is a Gram-stain-positive bacterium with eight subspecies, five of which have been redefined as different species on the basis of their genome sequence data. On the basis of the results of phylogenetic analysis of dnaA gene sequences, strains of members of the genus Clavibacter isolated from barley have been grouped in a separate clade from other species and subspecies of the genus Clavibacter . In this study, the biochemical, physiological, fatty acids and genetic characteristics of strains DM1T and DM3, which represented the barley isolates, were examined. On the basis of results from multi-locus sequence typing and other biochemical and physiological features, including colony colour, carbon source utilisation and enzyme activities, DM1T and DM3 are categorically differentiated from the aforementioned eight species and subspecies of the genus Clavibacter . Moreover, the results of genomic analysis reveal that the DNA G+C contents of DM1T and DM3 are 73.7 and 73.5 %, respectively, and the average nucleotide identity (ANI) values between DM1T and DM3 and other species and subspecies range from 90.4 to 92.0 %. The ANI value between DM1T and DM3 is 98.0 %. These results indicate that DM1T and DM3 are distinct from other known species and subspecies of the genus Clavibacter . Therefore, we propose a novel species, C. zhangzhiyongii, with DM1T (=CFCC 16553 T=LMG 31970T) as the type strain.