Competition between Rhizobium trvolii Strains for Nodulation, during Growth in a Fermenter, and in Soil-based Inoculants, Studied by ELISA

An improved ELISA technique using a new type of enzyme-conjugate- the antibody being linked to P-galactosidase by using a heterobifunctional reagent, N-succinimidyl-3-(2-pyridy1dithio)propionate (SPDP), containing two reactive groups directed towards different functional sites- has been further improved by fine purification of the antibodies. The ELISA was applied in studies of competition among strains of Rhizobium trifolii in three environments: a rhizosphere, a liquid medium and in soil. The strain origin of nodules formed by strain mixtures of different relative composition was investigated, including a study of double strain occupancy. Strain 7612 was found to compete successfully with strain 285 for nodulation. No double strain occupancy occurred. Strain 761 2 also competed successfully with strain 285 in soil, but strain 285 dominated when grown together with strain 7612 in a liquid medium in a fermenter