HIGHER BACTERIAL MOTILITY ENHANCES INFECTIVITY OF BRADYRHIZOBIUM JAPONICUM.

ALTHABEGOITI, M.J.; LÓPEZ GARCÍA, S.L.; MONGIARDINI, E.J.; PÉREZ GIMÉNEZ, J.; QUELAS, J.I.; LODEIRO, A.R.

Iguazú, Misiones

Congreso; XL Reunión Anual-SAIB; 2004

Sociedad Argentina de Investigación Bioquímica y Biología Molecular

 Motility of Bradyrhizobium japonicum in soil or vermiculite has been shown as scarce in the vertical direction. When a naturalized plant-compatible rhizobial population is established in the soil, this scarce vertical motility may prevent the nodulation by an inoculated strain applied to the seeds, because most of the inoculant remains in non-infectable root areas. Here we evaluated whether an increased rhizobial motility may enhance infectivity and nodule occupation. By means of a recurrent selection procedure we obtained a B. japonicum strain with higher motility than the wild-type, a phenotype that we called as Mot++. Growth rate and nodulation ability of Mot++ mutants were not affected, and the Mot++ phenotype was stable after passage through nodules. As the parent strain, the Mot++ strain had single polar flagella. The Mot++ strain displayed a higher rate to infect the emergent root hairs of young soybean plants. When applied to soybean seeds in competition with an isogenic rhizobial population established in the vermiculite substrate since 30 days before (107 cfu/ml free solution), a small increment in nodule occupation by the Mot++ strain was observed in relation to the wild-type. These results suggest that the increase in motility may be applied to improve inoculant competitiveness in field situations.