TAXONOMY OF XANTHOMONADS FROM CEREALS AND GRASSES BASED ON SDS-PAGE OF PROTEINS, FATTY-ACID ANALYSIS AND DNA HYBRIDIZATION

Strains of all Xanthomonas species, X. campestris pathovars pathogenic for cereals and grasses and strains of X. campestris pv. campestris were compared by SDS-PAGE of proteins, gas chromatography of fatty acid methyl esters and DNA-DNA hybridization. The groupings derived using all three methods correlated well with each other. Strains of X. axonopodis and X. campestris pv. vasculorum were heterogeneous, each comprising two groups (A and B); group A contained the type strain and pathovar reference strain, respectively. Besides the recognized Xanthomonas species X. albilineans, X. campestris, X. fragariae, X. maltophilia, X. oryzae and X. populi, the following five centres of variation could be delineated at DNA-binding levels of above 60%: (i) a group consisting of X. campestris pathovars translucens, hordei, cerealis, secalis, undulosa (the 'translucens group'), graminis, poae, arrhenatheri, phlei (the 'graminis group') and phleipratensis; (ii) X. axonopodis type A together with X. campestris pv. vasculorum type A and X. campestris pv. coracanae; (iii) a group of X. campestris pv. vasculorum type B and X. campestris pv. holcicola; (iv) Xanthomonas strains isolated from Bromus; and (v) strains isolated from sugarcane in Guadeloupe. The type B strains of X. axonopodis appeared to be misclassified in Xanthomonas. An interim proposal for an improved classification of Xanthomonas is presented on the basis of the data.