L-Canavanine made by Medicago sativa interferes with quorum sensing in Sinorhizobium meliloti.

Sinorhizobium meliloti is a gram-negative soil bacterium, capable of establishing a nitrogen-fixing symbiosis with its legume host, alfalfa (Medicago sativa). Quorum sensing plays a crucial role in this symbiosis, where it influences the nodulation process and the synthesis of the symbiotically important exopolysaccharide II (EPS II). S. meliloti has three quorum-sensing systems (Sin, Tra, and Mel) that use N-acyl homoserine lactones as their quorum-sensing signal molecule. Increasing evidence indicates that certain eukaryotic hosts involved in symbiotic or pathogenic relationships with gram-negative bacteria produce quorum-sensing-interfering (QSI) compounds that can cross-communicate with the bacterial quorum-sensing system. Our studies of alfalfa seed exudates suggested the presence of multiple signal molecules capable of interfering with quorum-sensing-regulated gene expression in different bacterial strains. In this work, we choose one of these QSI molecules (SWI) for further characterization. SWI inhibited violacein production, a phenotype that is regulated by quorum sensing in Chromobacterium violaceum. In addition, this signal molecule also inhibits the expression of the S. meliloti exp genes, responsible for the production of EPS II, a quorum-sensing-regulated phenotype. We identified this molecule as l-canavanine, an arginine analog, produced in large quantities by alfalfa and other legumes.

[Nutritional value and antinutritional factor content of precooked flours prepared from Canavalia ensiformis]. / Valor nutricional y contenido de factores antinutricionales de harinas precocidas de granos de Canavalia ensiformis.

Precooked flours obtained five Canavalia ensiformis varieties were prepared by dehydration in double drums. On a dry matter basis, significant differences (P < 0.05) among varieties were detected for crude protein content (25 to 30%), starch (36 to 40%) and dietary fiber (13 to 15%). Hemagglutinins were eliminated as result of the high temperature (146 degrees C/4 min) employed during the drying process. Similar results were not obtained for trypsin inhibitors and canavanine considering that small amounts of these compounds remained in the precooked flours prepared from canavalia seeds. A 10% decrease in available lysine was observed. Biological assays yielded Protein Efficiency Ratio (PER) values of 0, 8-1 and Neat Proteic Relation (NPR) values of 2-3-2.6. True digestibility of protein values were improved from 87 to 90%. All cultivars had similar starch digestive utilization coefficient (96%) and starch fraction (4%) resistant to enzymatic hydrolysis in the rat digestive tract.

Separation of canavanine and canaline by high performance liquid chromatography.

The plant amino acid canavanine and its hydrolytic product canaline were successfully separated and identified by Reverse Phase High Performance Liquid Chromatograph (RP-HPLC). This procedure was used to demonstrate the arginase-mediated cleavage of canavanine to yield canaline and urea, and the subsequent formation of a Schiff's base complex between canaline and pyridoxal phosphate. Both aforementioned reactions were demonstrated by RP-HPLC.