Fermentation optimization of a strain Bacillus methylotrophilusWM-1 against Aeromonas hydrophila

To investigate and obtain the best medium formula and fermentation conditions of an antagonistic strain WM-1 against Aeromonas hydrophila, we used A. hydrophila as the index bacteria of the antibacterial. The activity of strain WM-1 was measured by Oxford cup test. Single factor experiments and orthogonal experiments were employed to optimize the liquid medium compositions and fermentation conditions of WM-1. The data showed that the optimum medium included 1.0% soluble starch, 1.5% beef extract, 0.05% K₂HPO₄•3H₂O and 0.07% MgSO₄•7H₂O; and the optimal fermentation conditions were initial pH 7.5, culture temperature 30 °C, fermentation time 48 h, medium volumes 20%, rotating speed 210 r/min. Under the optimum conditions, the inhibition zone of WM-1 reached (22.5±0.50) mm, which was 40.6% higher than that under non-optimized conditions. These results provide a theoretical basis for the biocontrol of A. hydrophila.