Growth of Bradyrhizobium elkanii Strain BR 29 in culture media with different pH values

Currently soybean is the most economically important legume crop in Brazil. Due to its profitability soybean is being widely spread out all over the national territory. Some assays have shown low response of this crop to liming in acid Brazilian soil, under no-till age systems. Acidity is one of the factors that limit the efficiency of the symbiosis rhizobia - legumes. This problem could be solved if acid tolerant strains were obtained or if tolerance to acidity could be induced. Some papers demonstrated induced tolerance to acidity when the bacterium is previously exposed to a slightly acid pH. The aim of this study was to verify the growth of Bradyrhizobium elkanii strain Br 29 in culture media with different pH values (6.8; 6.0; 5.5). Two experiments were carried out with two different culture media varying mainly regarding initial pH. Strain growth, by optical density and colony forming units (CFU) number, and pH medium modification were evaluated. Growth curves varied either in accordance with pH or culture media composition. Growth based on maximum number of CFU.mL(-1) was better at pH 5.5 in Lopreto medium and at pH 6.0 at Lorda and Balatti medium. Better growth on lowest pH (5.5) was related to greater exopolyssacaride production.