TAXONOMIC SIGNIFICANCE OF 2,4-DIAMINOBUTYRIC ACID ISOMERS IN THE CELL-WALL PEPTIDOGLYCAN OF ACTINOMYCETES AND RECLASSIFICATION OF CLAVIBACTER-TOXICUS AS RATHAYIBACTER-TOXICUS COMB. NOV

An HPLC procedure which separates D- and L-amino acid isomers was appl ied to an analysis of peptidoglycan of 2,4-diaminobutyric acid (DAB)-c ontaining actinomycetes, The cell wall peptidoglycans of species of th e genera Agromyces, Clavibacter and Rathayibacter contain DAB and have been differentiated principally by their menaquinone profile, These p eptidoglycans are known to be identical in structure, all being of the B2 gamma type, possessing both D- and L-DAB, The type strains of all the subspecies of Clavibacter michiganensis have D- and L-DAB in almos t equal proportions in their cell wall peptidoglycan as previously rep orted. In contrast, the type strains of Clavibacter toxicus and all va lid species of the genera Agromyces and Rathayibacter contain the L-is omer of DAB almost exclusively. This characteristic is in good agreeme nt with phylogenetic analyses based on 16S rDNA sequences and menaquin one profiles. On the basis of these data, the transfer of Clavibacter toxicus to the genus Rathayibacter as Rathayibacter toxicus comb. nov, is proposed. The isomer profile of DAB is shown to be a good taxonomi c marker to differentiate these genera.