Production of antimicrobial metabolites by Bacillus subtilis and their applications

The present investigation was carried out to produce of antimicrobial metabolites by Bacillus subtilis during two successive seasons 2011 /2012. One bacterial strain was isolated from healthy leaves of infected cucumber plants with Pseudoperonospora cubensis or Sphaerotheca fuliginea. Spraying of cucumber plants was done with bioagent (108 CFU mL-1) under greenhouse conditions as protective treatment comparing with fungicides. The obtained results exhibited that all treatments reduced the disease severity comparing with control. The microbial bioagent was identified by using 16S rDNA sequencing technique as Bacillus subtilis. The maximum accumulation of metabolites occurred at the stationary phase. Metabolites accumulation coincided with increase in the specific growth rate and reduction of disease severity. Maximum activity of metabolites was at pH 7 and 30°C. Mode of metabolites action on (sporangiophore and sporaniga) of P. cubensis and (conidiophore and conidia) of S. fuliginea by examination of Scanning Electron Microscope and their identification by GC-MS was investigated. It was observed that collapse in sporangiophore, sporangia and conidia. These compounds mostly included fatty acids known as Hexadecanoic acid, n-Hexadecanoic acid, Octadecanoic acid, 8-Octadecanoic acid, 9-Octadecanoic acid, Pentadecanoic acid, Heptadecanoic acid, dodecatrienoic acid, Nonanoic acid and Decanoic acid. Sprayed plants recorded best results for peroxidase and polyphenol oxidase enzymes activity compared with unsprayed one. Antibiotics exhibited also antagonistic activity against of Staphylococcus aureus by inhibition zone formation. In conclusion, bioagent can be use as an alternative and safe method to fungicides in controlling downy and powdery mildew diseases of cucumber and inhibition of Staphylococcus aureus as pathogenic bacteria. © 2013 Asian Network for Scientific Information.