Rapid Assessment Of The Antagonistic Potential Of Bacillus Strains Against The Infection With Phytophthora Capsici And The Characteristics Of Lipopeptide Produced By Strain B006

In this study, A rapid method to assess the antagonistic potential of Bacillus strains against phytopathogens was reported by analysis of their biofilm formation, lipopeptide encoding genes, pepper radicle assays on agar plates, and the confirmation of the antagonism of several selected strains in the greenhouse. And the antibiotic substances produced by strain B006 was studied. Detailed results were listed as the following.Of 93 Bacillus strains tested, 48 strains had ability to form biofilm on polypropylene tube walls, and were subjected to PCR amplification as the DNA sources by use of the primers specific for lipopeptide encoding genes (srfAA, srfAB, ituC and fenD). The antagonistic ability of the strains forming biofilm and/or harboring lipopeptide coding genes against the infection with Phytophthora capsici was evaluated by radicle assays on agar plates. Fifteen strains had great antagonistic efficacy of above 50%, of which 8 strains varying in biofilm formation, antagonism and lipopeptide encoding genes were further tested in the greenhouse. The results indicated that the high-level biofilm formers (4 strains) harboring srfAA, srfAB and fenD that showed significant antagonism on plates had control efficacy of above 50% in greenhouse. The efficacy of middle-level biofilm formers (2 strains) harboring srfAA, srfAB, ituC and fenD in greenhouse was similar with that on plates. By combining the analysis of biofilm formation, lipopeptide coding genes and radicle assays on agar plates, this method was revealed to be rapid and efficient to screen Bacillus strains against phytophthora disease in pepper.Eight Bacillus strains selected via greenhouse test inhibited the hyphae growth of both Fusarium oxysporum and Phytophthora capsici in dual-culturing assay. The antibiotic metabolites produced by strain B006 in KMB broth was extracted, its ability to inhibit the growth of F. oxysporum was stronger than that of P. capsici. The metabolites produced by strain B006 were analyzed by HPLC-MS, and surfactin and fengycin were detected to be the main components. Detection of surfactin produced by strain B006 in broth of KMB, NA, Landy and SWB by HPLC-MS showed that KMB was the best broth, and detection of surfactin in KMB at 24, 36, 60, 72 and 96h showed that the highest production was at 72h.The solid phase extract (SPE) column was used to improve the extraction of surfactin from soil. Comparision of different elution conditions showed that washing buffer of methanol and water with the ratio of 1:1 could wash the column better than that the ration of 5:95. Extraction of surfactin from soil added with B006 fermented broth indicated that the extraction of surfactin was not affected obviously. And the detection of surfactin from pepper roots showed that surfactin could be examined from 3g roots other than the blank control roots without inoculation of B006. And the disease incidence of treatment with B006 was lower than that the control. The incidence of the treatment with B006 was 5.3% and 7.5%, respectively, while the incidence of the control was 35%.This study provides a value information in rapid screening of biocontrol strains and machanism of antibiotics in biological control.