The interaction of and : net H efflux stimulus and alteration of extracellular Na concentration

Abstract

We studied the effect of a lectin isolated from seeds of the legume Vatairea macrocarpa on net H+ efflux in Rhizobium tropici, a bacterium capable of nodulating legume Phaseolus vulgaris. V. macrocarpa lectin (VML) was observed to temporarily stimulate the specific net H(+) efflux in R. tropici. When VML was present at 32 microg ml(-1), with or without 2 microM galactose (Gal), a specific net efflux >2.4 pM H+(min)(-1) mg dry biomass(-1) was induced. There was no detectable net H+ efflux when bovine serum albumin (16 microg ml(-1)) was tested. Addition of 16 microgVMLml(-1) resulted in a 700% increase of the extracellular Na+ concentration. The soluble proteins in the supernatant containing VML extract indicate a maximum immobilization of +/-10 microgVMLml(-1), with a minimum of 36,600 dimers or 8500 larger aggregates of VML binding in each bacterium. Our data suggest that VML activates Rhizobium as a bioenergetic substrate molecule, resulting in potential alterations of the external bacterial membrane.

Effect of Leguminous Lectins on the Growth of Rhizobium tropici CIAT899

“…Previous studies with VML showed that this lectin was able to stimulate the metabolism of R. tropici by increasing the efflux of H + [ 15 ], as well as stimulating the respiration of R. tropici and R. etli [ 16 ]. The mechanisms underlying the effect of these lectins on rhizobial growth remain unclear.…”

“…These proteins mediate the attachment of rhizobia cells in the roots [ 9 ], agglutination of rhizobia near the roots [ 11 ] and recognition of nodulation factors [ 12 , 13 ]. Some studies showed that lectins may interact with rhizobia and modulate its metabolism, inducing the protein synthesis [ 14 ], increasing cellular respiration [ 15 ], stimulating the efflux of H + [ 16 ] and promoting bacterial growth [ 17 , 18 ]. Moreover, the use of lectins can enhance the symbiotic efficiency between rhizobia and host plant, leading to an improvement in plant productivity [ 19 , 20 ].…”