Identification Of Biocontrol Bacterial Strain BAB-1 Against Tomato Grey Mold And Optimization Of Its Fermentation

Antigonistic bacterial strain BAB-1 was isolated from cotton rhizosphere and showed strong inhibition against Botrytis cinerea Pers. This strain also displayed significant control efficacy against tomato grey mold under the field condition.In this study, the inhibitory activity against B.cinerea and biocontrol ability to tomato grey mold by strain BAB-1 was tested by using the cell free supernatant. In the double-layered plate test, large and clear inhibition zone was appeared round the oxford cup which contain the supernatant of strain BAB-1. The result indicated that strain BAB-1 could produce antifungal substance. The control effect of strain BAB-1 against tomato grey mold was 70.92% by using the detached leaf method.Strain BAB-1 was identified as Bacillus subtilis according to its morphological characteristics, 16S rDNA sequence and the testing result of API 50CHB system.16 different media for the bacterial growth and the antifungal substance producing was selected and tested. Results showed that the medium No. 3 was suitable for either bacterial growth or the antifungal substance production. The cell of strain BAB-1 reached the highest after 28 hours culturing, meanwhile the supernatant showed the strongest antifungal activity against B. cinerea after 48 hours culturing. Optimum fermentation condition for the cell growth of strain BAB-1 were as followed: temperature 30℃, 210 rpm, pH 7.24, inoculation amount 3% and amount of loading 70mL in 250mL flask, the cell density could reach 1.63×109cfu/mL. The optimum conditions for the antifungal substance production were temperature 30℃, 210 rpm, pH7.24, inoculation amount 2% and amount of loading 100mL in 250mL flask. Under the optimum conditions, the inhibition zone of strain BAB-1 against B. cinerea could reach 1.81cm width.The medium components was further optimized by using single factor and the orthogonal testings. The optimum medium was as followings: starch 4%, glucose 2.5%, peptone 0.05%, NaNO3 0.3%, CaCO3 0.12%, MgSO4 0.15%, K2HPO4 0.25%, MnSO4 0.035%. Finally, the cell production, antifungal activity and the lipopeptide production of strain BAB-1 was compared by using three kinds of media, Medium No.8, Medium No.3 and Medium modified 3. The result proved that the optimum medium of strain BAB-1 was Medium modified 3.