Analysis of cellular fatty acids and phenotypic relationships of Agrobacterium, Bradyrhizobium, Mesorhizobium, Rhizobium and Sinorhizobium species using the Sherlock Microbial Identification System

Previous studies have demonstrated that cellular fatty acid analysis is a u seful tool for identifying unknown strains of rhizobia and establishing tax onomic relationships between the species. In this study, the fatty acid pro files of over 600 strains belonging to the genera Agrobacterium, Bradyrhizo bium. Mesorhizobium, Rhizobium and Sinorhizobium were evaluated using the g as-chromatography-based Sherlock Microbial Identification System (MIS). Dat a collected with the MIS showed that the three phylogenetically defined bio vars of the genus Agrobacterium formed discrete clusters, whilst species be longing to the genus Mesorhizobium formed three subclusters which were easi ly distinguished. These three subclusters contained Mesorhizobium ciceri an d Mesorhizobium mediterraneum, Mesorhizobium tianshanense fatty acid group I and Mesorhizobium plurifarium, and Mesorhizobium huakuii and Mesorhizobiu m loti. The genus Sinorhizobium was composed of an individual position for Sinorhizobium meliloti and a large cluster comprising Sinorhizobium fredii, Sinorhizobium saheli, Sinorhizobium terangae. Sinorhizobium kostiense and Sinorhizobium arboris. S. meliloti contained significantly higher levels of the fatty acid 19:0 cycle omega 8cis and clustered with Rhizobium sp. (Hed ysarum coronarium). However, discrimination between the species of genera S inorhizobium and Rhizobium was a function of the concentration of 16:0 3-OH . The genus Rhizobium contained a single duster containing Rhizobium sp. (H edysarum coronarium). Rhizobium gallicum, Rhizobium leguminosarum and Rhizo bium etli, along with individual positions for Rhizobium giardinii, Rhizobi um tropici, Rhizobium galegae and Rhizobium hainanense. R. tropici and R. h ainanense exhibited similarity to Agrobacterium biovar 2, whilst R. galegae was similar to Agrobacterium biovar 1. R. giardinii appeared unique, with comparatively little similarity to the other species. Analysis of the genus Bradyrhizobium revealed large differences from the other genera studied. T wo subgroups of Bradyrhizobium elkanii were detected and easily distinguish ed from Bradyrhizobium japonicum. Bradyrhizobium liaoningense and Bradyrhiz obium sp. (Arachis hypogaea), a group isolated from Chinese peanut plants, showed similarities to B. japonicum, whilst a subgroup of M. tianshanense a ppeared identical to Bradyrhizobium sp. (Arachis hypogaea).