First, in the 1H spectrum, a doublet at 4.87 ppm (J 7.9 Hz) was unequivocally assigned to the anomeric hydrogen of a β-glycoside
unit. Second, the combination of the COSY and NOESY spectra (not shown) and the 1H-13C HSQC spectrum permitted the assignment of all proton and carbon signals in the compound (Table 1). Third, the HMBC experiment confirmed a 1→2 link between two monosaccharide, unsubstituted, molecules (GSK1120212 order Figure 9A). Finally, the mass spectrum showed a peak at m/z 1400 corresponding to [M+Na]++, from which we could deduce a molecular weight of 2754, corresponding to 17 β-glucopyranose units. On the basis of this result, the BVD-523 research buy structure of the compound was established as a cyclic (1→2)-β-glucan formed by 17 β-glucopyranose units (Figure 9B). This compound had been previously described as an extracellular glucan secreted by R. tropici CIAT 899 [34]. Our results clearly indicate that, as expected, the R. tropici CIAT 899 cyclic (1→2)-β glucan is also cell-associated. Table 1 1H and 13C NMR data (δ, ppm) for the R. tropici CIAT 899 cyclic (1→2)-β-glucan 1 2 3 4 5 6 H 4.87 3.59 3.79 3.48 3.52 3.95, 3.74 C 102.6 82.5 76.1 69.5 77.0 61.3 a 1H and 13C click here signals were referenced to internal
tetramethylsilane. Figure 9 Identification of the R. tropici CIAT899 cyclic (1→2)-β-glucan. (A) HMBC spectrum of intracellular solutes accumulated by R. tropici CIAT899 grown in MAS medium with mannose and 100 mM NaCl. (B) Chemical structure of the cyclic (1→2)-β-glucan. Discussion In this work, we investigated the osmoadaptive mechanisms used by four native rhizobia isolated from root nodules of P. vulgaris cultivated in north Tunisia [23]. Strains R. etli 12a3, R. gallicum bv. phaseoli 8a3 and R. leguminsarum 31c3 are
potentially good inoculants as they were infective and showed efficient nitrogen fixation in symbiosis with P. vulgaris [23]. filipin In addition, Agrobacterium 10c2 was able to colonize preformed P. vulgaris nodules [28] and to specifically favour nodulation by some local strains [29], suggesting that it might be used as co-inoculant. Our results confirm the strain affiliations proposed by Mhandi et al. [24, 28]. In addition, on the basis of its phylogenetic relatedness to the A. tumefaciens type strain, Agrobacterium 10c2 is proposed in this work to be renamed as A. tumefaciens 10c2. As shown by 13C- and 1H-NMR analyses, the long-term response of the four Rhizobium strains to NaCl involved the accumulation of trehalose, mannitol and glutamate; but the latter one was only observed in R. leguminsarum 31c3 and R. tropici CIAT 899. The reason why glutamate was not present in the extracts of R. gallicum bv. phaseoli 8a3 and R. etli 12a3 is unknown.