tropici CIAT 899T, a Latin American isolate that has been shown to tolerate several abiotic stresses, including high temperature, low pH, or salinity [15, 25, 26]. Despite a number of R. tropici CIAT 899 osmosensitive mutants has been characterized, none of them was affected in compatible solute synthesis [26, 27]. In fact, the complete set of compatible solutes in this strain was unknown previously to this work. Second, we aimed to determine the osmoadaptive mechanism of Agrobacterium sp. 10c2 (proposed in this

paper as A. tumefaciens 10c2), which was isolated from the same Tunisian common bean fields as the above strains [24]. Agrobacterium sp. 10c2 could not nodulate P. vulgaris per se, but it was able to Akt inhibitor colonize pre-formed P. vulgaris nodules [28] and to modulate, either positively or negatively, nodulation of common beans by native selleck products rhizobia [29]. Third, we focused on trehalose, which we found as the major compatible solute in the four Rhizobium strains. We determined the trehalose content of the strains and traced its biosynthetic pathway both molecularly and biochemically. Collaterally, the β-1,2-cyclic glucan from R. tropici CIAT 899 was co-extracted KPT-330 order with the cytoplasmic compatible solutes when cells were grown at low salinity, and its chemical structure was determined by using

a suite of one-dimensional and two-dimensional NMR spectra and mass spectrometry. Results Strain identity and phylogeny Strains R. gallicum bv. gallicum 8a3, R. etli 12a3, Agrobacterium sp. 10c2 and R. leguminosarum bv. phaseoli 31c3 were previously isolated by Mhamdi et al. [23] from nodules of P. vulgaris grown on neutral soil samples collected from North

Tunisia. A preliminary strain affiliation was made upon RFLP Phospholipase D1 analysis of the 16S rRNA, nodC and nifH genes [24], and partial sequence of the 16S rDNA and BLAST search for homologous sequences (for Agrobacterium sp. 10c2 [28]). To confirm the identity and phylogenetic position of the strains, we sequenced their nearly complete 16S rDNA Figure 1 shows the phylogenetic tree constructed using the neighbor-joining method based on these sequences and those of closely related rhizobia obtained from GeneBank. Strains R. etli 12a3, R. gallicum bv. phaseoli 8a3, and Agrobacterium sp. 10c2 grouped with the R. etli, R. gallicum and A. tumefaciens type strains. On the basis of its phylogenetic relatedness to the type strain of A. tumefaciens, we propose strain Agrobacterium sp. 10c2 to be named as A. tumefaciens 10c2. R. leguminosarum bv. phaseoli 31c3 was in the same cluster as the type strains of R. leguminosarum bvs. trifolii and viciae, but in a separate branch. Interestingly, the type strain of R. leguminosarum bv. phaseoli, was in a separate group, close to the R. etli type strain. This lack of clustering between the type strains of R. leguminosarum bv. phaseoli and the other two biovars of R. leguminosarum was previously reported [30], and it was proposed that R.