Distribution of antimicrobial lipopeptides in Bacillus and Pseudomonas spp., two genera with antagonistic effects against plant pathogens

Abstract

Suppressive soils, composts, and compost teas have previously shown inhibitory effects against plant disease. A major reason for this suppressiveness has been their beneficial microbial populations. The present study was carried out to investigate the inhibitory activity of forty bacteria isolated from these three sources against the mycelial growth of six plant pathogens.Thirty-eight isolates inhibited at least one of the pathogens whereas sixteen of the isolates inhibited all the pathogens (36% average inhibition). Crude lipopeptides extracts were precipitated from bacterial liquid cultures. All tested lipopeptide samples inhibited the mycelial growth or conidial germination of at least one of the pathogens. Known antimicrobial lipopeptides in selected samples were identified by LC-MS. Results showed that all Bacillus and Bacillus-related spp. produced one or more lipopeptides from the fengycin, iturin, and surfactin families. In addition, certain Pseudomonas spp. produced lipopeptides from the amphisin and putisolvin families.iii Acknowledgments It is with immense gratitude that I acknowledge the support and help of my supervisor, Dr. Tyler Avis. He has been the pivotal point of my academic growth. Dr. Avis' passion and positive attitude towards learning and teaching science has encouraged my educational aspirations. I sincerely thank him for allowing me to pursue research in his lab for five years.