Optimization of culture medium for a Bradyrhizobium japonicum strain introduced from Russia

Abstract

The aim and tasks of the study. The study was aimed at determination of ingredients and their concentrations to culture medium YMA, which would be the most suitable for cultivation of soybean nodule bacteria Bradyrhizobium japonicum. This will provide a scientific rationale for the production of nodule bacteria on an industrial scale.

Materials and methods. The starting material was soybean nodule bacteria B. japonicum, strain GF, introduced from the All-Russian Research Institute of Soybean of the Russian Agricultural Academy. Culture media were YMA, SM, TY, PA, BSE.

Concentrated solution of bacteria was cultured for two days at 28 ° C, then was spread in liquid nutrient medium YMA and cultured for four days. Thereafter, B. japonicum was devided among four media in 250 flasks of 100 ml. Optimal medium was spectrophotometrically determined for different periods of bacterium growth by growth curves. Thereafter, nutrient medium composition and concentration of its ingredients were optimized. In particular, mannitol in nutrient medium YMA was replaced with the same amount of glycerol, lactose, dextrose, sucrose, and maltose, while the other ingredients remained unchanged.

Results and discussion. The results showed that B. japonicum cells grew the fastest in nutrient medium YMA as compared with the others - SM, TY, PA, BSE. Thus, culture medium YMA was chosen to optimize the composition.

The growth rate of B. japonicum enhanced, when carbon from different  sources was added to nutrient medium. Among several sources (glucose, mannitol, sucrose, glycerytan), glucose was the best. In terms of strain GF growth it was found that the optimal ratio of ingredients and concentrations was 10.0 g / L of glucose, 0.8 g / L of yeast powder, 0.2 g / L of MgSO₄ • 7H₂O, 0.8 g / L of K₂HPO₄, 0.1 g / L of NaCl, 0.01 g / L of CaCl₂, and 4 ml / L of Rh solution.

Optimized culture medium was compared with original medium YMA and medium 3. Results of culturing bacteria 12, 24, 36 and 48 hours after inoculation were assessed. It was proved that optimized nutrient medium by these parameters was better than original one and number 3.

Conclusions. The study revealed that of the five culture media YMA was the best to inoculate soybean nodule bacteria B. japonicum, strain GF. Its composition was optimized, and it was demonstrated that the best ingredients and their concentrations were 10.0 g / L of glucose, 0.8 g / L of yeast powder, 0.2 g / L of MgSO₄ • 7H₂O, 0.8 g / L of K₂HPO₄, 0.1 g / L of NaCl, 0.01 g / L of CaCl_2, and 4 ml / L of Rh solution. Optimized culture medium YMA will enable the production of nodule bacteria on an industrial scale in a short time.