Early interactions of Bradyrhizobium japonicum and soybean roots: specificity in the process of adsorption.

LODEIRO, A.R.; FAVELUKES G.

SOIL BIOLOGY AND BIOCHEMISTRY

Pergamon Press

Año: 1999 vol. 31 p. 1405 - 1411

0038-0717

Specificity in the process of adsorption of Bradyrhizobium japonicum to soybean roots (Glycine max Merril.) was studied with a standardized procedure that quantifies adsorbed rhizobia to young seedlings from dilute suspensions (in the range of 103 bacteria ml-1) of an antibiotic-resistant strain of B. japonicum. Adsorption of this strain was maximal in the late-exponential growth phase. Adsorption was rapid, without an initial lag, and slowed down after one hour, approaching a plateau after four hours. This occurred either in absence or presence of Ca2+ plus Mg2+ ions. Adsorption of the indicator strain at a constant concentration of 103 rhizobia ml-1 was increasingly inhibited by the presence of antibiotic-sensitive competitor strains at a concentration ranging from 103 to 108 bacteria ml-1. In the range of 105-107 competitor rhizobia ml-1, a heterologous competitor inhibited adsorption of the indicator strain significantly less than a homologous competitor, indicating the occurrence of symbiont-specific adsorption events. Evidence of adsorption specificity also was shown by competition against a range of heterologous and homologous strains. Specific adsorption did not required the presence of Ca2+ plus Mg2+ ions. By incubating B. japonicum with soybean roots in the presence of an heterologous competitor strain and different concentrations of either the soybean lectin hapten N-acetyl-D-galactosamine, or the B. japonicum BJ38 lectin inducer and hapten lactose, it was observed that N-acetyl-D-galactosamine had no effect on specific adsorption, whereas lactose at 0.1 mM stimulated specific adsorption by 105%, and at 10.0 mM inhibited it by 65%.