IDENTIFICATION OF AGROBACTERIUM AND RIZOBIUM SPECIES BASED ON CELLULAR FATTY-ACID COMPOSITION

The increasing number of phylogenetically defined species in the gener a Agrobacterium, Rhizobium and Sinorhizobium suggests a need for a rap id identification method which will distinguish between these species. We have examined 65 strains of Agrobacterium representing: A. tumefac iens, (34); A. rhizogenes, (16) A. vitis, (10) Al rubi (2) and some un classified strains, and 150 strains of Rhizobium and Sinorhizobium rep resenting: R. etli (21); R. galegae (20); R. huakuii (17); R, legumino sarum (20); R. loti (16); R. topici (18); S. fredii( 19); and S. melil oti (20). Fatty acid methyl esters (FAME) were obtained from each stra in, as previously described, and analysed by gas-chromatography using the MIDI Hewlett-Packard Microbial Identification System (MIS). Fatty acid profiles were recorded, characteristic fatty acids noted and the overall similarities between fatty acid profiles for each species calc ulated. Relationships between species were also derived from the fatty acid data by principal component analysis. This showed overlapping cl usters for strains of R, leguminosarum and R, etli, R. topici and A. r hizogenes and S. fredii and S. meliloti within one supercluster. Strai ns of A. tumefaciens, A I nbi, A. vitis and R. galegae formed a second supercluster while R. loti and R. huakuii strains formed a third clus ter well separated from all the other strains. The fatty acid profiles were used to correctly identify at least 94% of the strains represent ing each species in the collection except R. etli. R. etli strains (23 .8%) were misidentified as R. leguminosarum. This was attributed to th e high similarity (44.7%) between R. etli and R. leguminosarum. It is concluded that whole cell fatty acid analysis should form part of the polyphasic description of new species of root nodule bacteria, with th e proviso that growth conditions and analytical methods be carefully s tandardized. It is suggested that FAME-MIS system and the database we have compiled provide a basis for future development.