APPLICATION OF FATTY-ACID METHYL-ESTERS FOR THE TAXONOMIC ANALYSIS OFTHE GENUS XANTHOMONAS

Gas-liquid chromatographic analysis was applied to examine whole-cell fatty acid methyl esters (FAMEs) of a total of 975 strains which inclu ded representatives of all seven Xanthomonas species (X. albilineans, X. axonopodis, X. campestris, X. fragariae, X. maltophilia, X. oryzae and X. populi), 134 X. campestris pathovars and two X. oryzae pathovar s as well as some related strains. At least 65 different fatty acids w ere found within the members of the genus Xanthomonas. A set of nine f atty acids (11:0 iso, 11:0 iso 3OH, 12:0 3OH, 13:0 iso 3OH, 15:0 iso, 16:1 cis 9, 16:0, 17:1 iso F and 17:0 iso) occurred in more than 99% o f the 966 genuine Xanthomonas strains and are therefore considered as the most common fatty acids for the genus Xanthomonas. The three fatty acids 11:0 iso, 11:0 iso 3OH and 13:0 iso 3OH are characteristic for all members of the genus Xanthomonas and serve as a useful criterion t o differentiate Xanthomonas from other bacteria. Cluster analysis reve aled 31 major FAME clusters within the genus Xanthomonas. The Xanthomo nas species X. albilineans, X. axonopodis, X. fragariae, X. maltophili a and X. populi each constituted a separate FAME cluster. Two FAME clu sters were formed within X. oryzae, corresponding to pvs. oryzae and o ryzicola, respectively. The species X. campestris was demonstrated to be heterogeneous and comprised 24 FAME clusters. In some cases, X. cam pestris pathovars which were isolated from related host plants grouped together. This was the case for the following pathovars from grasses: X. c. pvs. graminis, poae and phleipratensis (FAME cluster-7); X. c. pvs. arrhenatheri and phlei (FAME cluster 8), and also for the followi ng X. campestris pathovars from cereals: X. c. pvs. cerealis, hordei, undulosa, secalis and translucens (FAME cluster 9). All six X. campest ris pathovars from the crucifers (X. c. pvs. aberrans, armoraciae, bar bareae, campestris, incanae and raphani) fell within FAME cluster 2. M any Xanthomonas campestris pathovars from legumes were grouped within FAME cluster 1. Although most X. campestris pathovars were homogeneous or had only one or a few atypical strains, some X. campestris pathova rs were found to be heterogeneous. The greatest heterogeneity occurred in X. c. pvs. vasculorum and citri, forming 4 and 3 FAME subgroups, r espectively. Other X. campestris pathovars which constituted more than one FAME subgroup included X. c. pvs. phaseoli and vignicola. The com parison of the results of FAME analysis and those of phenotypic tests, SDS-PAGE of whole-cell proteins and DNA-DNA hybridization is discusse d. A database generated by the authors based on the fatty acid composi tions of Xanthomonas allows rapid identification of unknown xanthomona ds at the genus, species and often at pathovar level.