NUMERICAL CLASSIFICATION OF CORYNEFORM BACTERIA AND RELATED TAXA

A numerical taxonomy of 604 strains of the genera Arthrobacter, Aureob acterium, Brevibacterium, Cellulomonas, Clavibacter, Corynebacterium, Curtobacterium, Microbacterium, Nocardia, Nocardioides, Rhodococcus, T errabacter and Tsukamurella was undertaken based on 280 physiological characters with the aid of miniaturized tests. Clustering was by the u nweighted pair group method (UPGMA) with 12 different measures of simi larity. Test error, overlap between the phena and cophenetic correlati on coefficients for the classifications obtained with the Jaccard coef ficient (S(J)), the Pearson coefficient (S(P)), the simple-matching co efficient (S(SM)), and the Dice coefficient (S(D)) as measures of simi larity were within acceptable limits. Clusters were defined at the 55. 0 to 70.5% levels (S(J)). The compositions of clusters corresponded la rgely the delineations of 81.1 to 93.5% (S(SM)), 29.1 to 55.0% (S(P)), and 55.3 to 81.1% (S(D)). A total of 31 major clusters (containing fi ve or more strains), 41 minor clusters and subclusters (containing les s than five strains), and 54 single-member clusters were obtained in t he UPGMA/S(J) study. The following conclusions were reached: (i) A hig h degree of similarity between the genera Aureobacterium, Cellulomonas , Clavibacter, Curtobacterium and Microbacterium found in phylogenetic -based studies could be shown also phenetically. Strains belonging to these genera were found in S(J) clusters 1 to 45, often representing c losely related, or single species. (ii) Several strains of the plant p athogenic coryneform bacteria assigned to the genus Clavibacter and Cu rtobacterium flaccumfaciens were found to be within one S(J); cluster, indicating the high similarity between these genera. The current clas sification of species within the genera Curtobacterium and Clavibacter is unsatisfactory; a close relationship to Microbacterium suggests a reclassification into a redefined genus. Subspecies of Clavibacter and pathovars of Curtobacterium flaccumfaciens should only be retained fo r practical purposes. (iii) Bacteria belonging to the genus Corynebact erium, including Corynebacterium glutamicum, C. ammoniagenes, C. minut issimum, C. striatum, C. variabilis, C. kutscheri, C. diphtheriae, C. pseudotuberculosis, and 'C. ulcerans' formed a separate complex of the distinct, adjacent clusters 47 to 63. The physiologically inactive sp ecies C. mycetoides, C. pseudodiphtheriticum, C. xerosis, C. renale an d C. pilosum were found in clusters 116 to 126. (iv) Differences betwe en the Arthrobacter globiformis group and the Arthrobacter nicotianae group were reflected in the structure of the phenogram, species differ entiation being based on only a few characters. (v) Strains assigned t o the four species of the genus Brevibacterium were grouped into two c lusters; the taxonomic implications are discussed. (vi) The results of the study are largely in line with a previously published numerical s urvey and with chemotaxonomic and genetic data. Suggestions for an imp roved classification for some species is given in addition to an exten sive data-base on physiological reactions for differentiation purposes .