Kinetic sedimentation of Rhizobium-aggregates produced by leguminous lectins

Abstract

Lectins from Canavalia brasiliensis (CnBr), Cratylia floribunda (CFL), Vatairea macrocarpa (VML) and Phaseolus vulgaris (PHA) aggregate Rhizobiumbacteria. The relationship between specific sedimentation rate, ν′ (based on bacterial dry biomass) of bacterial aggregates and lectin concentrations was hyperbolic and showed bacterial surface affinity by lectins. R. tropici (Rt), R. leguminosarum bv. phaseoli (Rlp) and R. etli (Re) surfaces showed predominantly receptors of galactosidic nature. The Rt surfaces showed very high affinities (k s = ±8.6 × 10−8 ag lectin protein ml−1) by Gal-specific lectins (PHA and VML), and very low affinities (ks=± 4.9 × 10−6) by Glc-specific lectins (CnBr and CFL). The Rlp surface had intermediate affinities by lectins. The Re surface showed high affinities by PHA (ks= ±1.26 × 10−8) and intermediate affinities by VML, CnBr and CFL. The relationship between sedimentation specific ν′′ (based on lectin weight) and bacterial density was a sigmoid and showed lectin affinity by Rt surfaces. The bacterial sedimentation showed positive cooperative binding of lectins. The V′′max induced by Glc-specific lectins was ±20 of that produced by Gal-specific lectins. The PHA affinity (ks= 1.19 mg dry biomass ml−1) was larger than VML (ks = 1.23). The Glc-specific lectin affinities were smaller than those of Gal-specific. The apparent binding site number of lectins (napp) was: 2.7-PHA; 2.2-VML; 3.2-CFL and 3.2-CnBr. The dissociation constant, ks, of lectin-binding kinetics decreased with sugar-hapten treatment (10 μM). The napp decreased in PHA and CFL, increasing in VML + sugar-hapten treatment. This study showed that there is a difference in Rhizobium surfaces for lectin binding.