Application of Fatty Acid Methyl Esters for the Taxonomic Analysis of the Genus Xanthomonas

Abstract

Gas-liquid chromatographic analysis was applied to examine whole-cell fatty acid methyl esters (FAMEs) of a total of 975 strains which included 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 pathovars as well as some related strains. At least 65 different fatty acids were found within the members of the genus Xanthomonas. A set of nine fatty 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% of 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 to differentiate Xanthomonas from other bacteria. Cluster analysis revealed 31 major FAME clusters within the genus Xanthomonas. The Xanthomonas species X. albilineans, X. axonopodis, X. fragariae, X. maltophilia and X. populi each constituted a separate FAME cluster. Two FAME clusters were formed within X. oryzae, corresponding to pvs. oryzae and oryzicola, respectively. The species X. campestris was demonstrated to be heterogeneous and comprised 24 FAME clusters. In some cases, X. campestris 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 following X. campestris pathovars from cereals: X. c. pvs. cerealis, hordei, undulosa, secalis and translucens (FAME cluster 9). All six X. campestris pathovars from the crucifers (X. c. pvs. aberrans, armoraciae, barbareae, campestris, incanae and raphani) fell within FAME cluster 2. Many 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 pathovars were found to be heterogeneous. The greatest heterogeneity occurred in X. c. pvs. vasculorum and citri, forming 4 and 3 FAME subgroups, respectively. Other X. campestris pathovars which constituted more than one FAME subgroup included X. c. pvs. phaseoli and vignicola. The comparison of the results of FAME analysis and those of phenotypic tests, SDS-PAGE of whole-cell proteins and DNA-DNA hybridization is discussed. A database generated by the authors based on the fatty acid compositions of Xanthomonas allows rapid identification of unknown xanthomonads at the genus, species and often at pathovar level.