Respiratory stimulus in Rhizobium sp. by legume lectins

High molecular weight lectins (> 100 kDa) from seeds of the legumes Canavalia brasiliensis (CnBr), Cratylia floribunda (CFL), Phaseolus vulgaris (PHA) and Vatairea macrocarpa (VML), temporarily stimulate the respiration of Rhizobium tropici-CIAT899 and R. etli-CFN42. These stimulants were significant (P < 0.05) in bacterial suspensions (> 2.85 mg dry biomass ml^sup -1^), having at least 6200 molecules of lectins per bacteria. The VML (20 μg ml^sup -1^), induced specific O^sub 2^ demand of 2.3-2.5 ηM O^sub 2^ min^sup -1^ mg dry biomass^sup -1^, in CFN42 and CIAT899, respectively. However, CnBr, CFL and PHA induced smaller demands of O^sub 2^ (5×), in both strains. The order of affinities of the lectins was approximately VML > PHA > CFL > CnBr, with regard to respiratory stimuli in CIAT899 strain. The co-administration of 10 μg VML ml^sup -1^ and 9.8 ηM galactose, in CIAT899 suspensions, reduced the respiratory stimuli significantly in relation to the treatment with VML alone. These respiratory stimuli, induced by the lectins, increase the significance of the interaction lectin × Rhizobium in terms of bacterial physiology. Its understanding could be important in relation to bacterial symbiotic behaviour.[PUBLICATION ABSTRACT]