Preliminary Study On The Mechanism Of Enhancing The Antibacterial Ability Of Bacillus Sp. BL-21 And HNDF2

Bacillus laterosporus BL-21 and Bacillus subtilis HNDF2 are antagonistic bacteria on plant soil-borne diseases of soybean root rot,which played an important role in biocontrol.The test studied the antagonistic effect of the mixed fermentation,compared strain BL-21 and HNDF2 single fermentation supernatant and 1:1 mixed fermentation supernatant antifungal activity of the soybean root rot pathogen Fusarium oxysporum.Then,the physical and chemical properties of the antimicrobial active metabolites produced by single fermentation and mixed fermentation of strains BL-21and HNDF2 were evaluated.By TLC and non-denaturing PAGE electrophoresis separated and analyzed the antibacterial substances in the single and mixed fermentation supernatant.Subsquently,the effect of strain HNDF2 and its metabolites on the antimicrobial substances produced by strain BL-21 in mixed fermentation were studied by bioassay method,as well as the effect of other bacteria on stains of BL-21and HNDF2.Initially analyzed the enhanced antimicrobial activity mechanism of bacillus BL-21 and HNDF2 mixed fermentation.The result of the antagonistic effect of the mixed fermentation showed that the inhibition zone diameters of BL-21 and HNDF2 supernatant of single fermentation liquid and mixed fermentation liquid on Fusarium oxysporum were 17.67±0.44 mm,9.83±0.56 mm and 21.67±0.44 mm,respectly.After significant analysis,the inhibitional activity of mixed fermentation was significantly higher than single fermentation.The result of physical and chemical properties of the antimicrobial active metabolites in mixed fermentation supernatant showed that the mixed fermentation supernatant in pH range from 5 to 9,and between 60⁹0?temperature short time?20 min?were pH and thermal stable.As well as,the mixed fermentation supernatant have a good protease stability and broad-spectrum antimicrobial activity on various of gram-negative,gram-positive bacteria and plant pathogenic fungi.In addation,BL-21and HNDF2 mixed fermentation supernatant and single fermentation supernatant were studied through ultraviolet spectrum.Antimicrobial substances were separated by TLC and PAGE,and the antifungal activity was determined,respectly.The result also proved in process of mixed fermentation,HNDF2 promoted BL-21 produced more antimicrobial substances.BL-21 and HNDF2 cell morphology observation and mutual antagonism tests showed,BL-21and HNDF2 had a mutual antagonism and the dominant bacteria was strain BL-21 in the mixed fermentation liquid.The effect of strain HNDF2 and its metabolites on the antimicrobial substances produced by strain BL-21 in mixed fermentation test showed that the strain age for 48 h of HNDF2 seed liquid with BL-21seed liquid mixed fermentation 48 h,which abtained the strongest inhibitory activity.The molecular weight of 63 kD?i.e.Electrophoretic band F₉?in HNDF2 fermentation liquid is separated by non-denaturing PAGE,which can play the same role with HNDF2 fermentation supernatant and promote BL-21 produce antimicrobial substances in the mixed fermentation process.The effect of other bacteria on the antimicrobial substances produced by stain BL-21 and HNDF2 showed that the antimicrobial activity of BL-21 or HNDF2 strain with other bacterial mixed fermentation did not enhancer than each bacterium fermentation alone and the result of HNDF2 can stimulate other Gram-positive bacteria enhanced antibacterial activity phenomenon needs further study.