Biosynthesis of compatible solutes in rhizobial strains isolated from Phaseolus vulgaris nodules in Tunisian fieldsReport as inadecuate

Biosynthesis of compatible solutes in rhizobial strains isolated from Phaseolus vulgaris nodules in Tunisian fields - Download this document for free, or read online. Document in PDF available to download.

BMC Microbiology

, 10:192

First Online: 16 July 2010Received: 24 April 2010Accepted: 16 July 2010


BackgroundAssociated with appropriate crop and soil management, inoculation of legumes with microbial biofertilizers can improve food legume yield and soil fertility and reduce pollution by inorganic fertilizers. Rhizospheric bacteria are subjected to osmotic stress imposed by drought and-or NaCl, two abiotic constraints frequently found in semi-arid lands. Osmostress response in bacteria involves the accumulation of small organic compounds called compatible solutes. Whereas most studies on rhizobial osmoadaptation have focussed on the model species Sinorhizobium meliloti, little is known on the osmoadaptive mechanisms used by native rhizobia, which are good sources of inoculants. In this work, we investigated the synthesis and accumulations of compatible solutes by four rhizobial strains isolated from root nodules of Phaseolus vulgaris in Tunisia, as well as by the reference strain Rhizobium tropici CIAT 899.

ResultsThe most NaCl-tolerant strain was A. tumefaciens 10c2, followed in decreasing order by R. tropici CIAT 899, R. leguminosarum bv. phaseoli 31c3, R. etli 12a3 and R. gallicum bv. phaseoli 8a3. C- and H-NMR analyses showed that all Rhizobium strains synthesized trehalose whereas A. tumefaciens 10c2 synthesized mannosucrose. Glutamate synthesis was also observed in R. tropici CIAT 899, R. leguminosarum bv. phaseoli 31c3 and A. tumefaciens 10c2. When added as a carbon source, mannitol was also accumulated by all strains. Accumulation of trehalose in R. tropici CIAT 899 and of mannosucrose in A. tumefaciens 10c2 was osmoregulated, suggesting their involvement in osmotolerance. The phylogenetic analysis of the otsA gene, encoding the trehalose-6-phosphate synthase, suggested the existence of lateral transfer events. In vivoC labeling experiments together with genomic analysis led us to propose the uptake and conversion pathways of different carbon sources into trehalose. Collaterally, the β-1,2-cyclic glucan from R. tropici CIAT 899 was co-extracted with the cytoplasmic compatible solutes and its chemical structure was determined.

ConclusionsThe soil bacteria analyzed in this work accumulated mainly disaccharides in response to NaCl stress. We could not find a direct correlation between the trehalose content of the rhizobial strains and their osmotolerance, suggesting that additional osmoadaptive mechanism should be operating in the most NaCl-tolerant strain R. tropici CIAT 899.

AbbreviationsNMRnuclear magnetic resonante



COSYcorrelated spectroscopy

HSQCheteronuclear single-quantum coherente

HMBCheteronuclear multiple-bond correlation

NOESYnuclear Overhauser effect spectroscopy

MSmass spectrometry

Electronic supplementary materialThe online version of this article doi:10.1186-1471-2180-10-192 contains supplementary material, which is available to authorized users.

Cristina Fernandez-Aunión, Thouraya Ben Hamouda contributed equally to this work.

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Author: Cristina Fernandez-Aunión - Thouraya Ben Hamouda - Fernando Iglesias-Guerra - Montserrat Argandoña - Mercedes Reina-Bueno



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