Analysis of active antifungal compounds produced by Paenibacillus polymyxa TP3

Botrytis cinerea is one of the major pathogens in the cultivation of strawberry.Strawberry is a kind of continual harvest crop; spraying pesticides is necessary to reduce the loss caused by gray mold and difficult to have safety harvest period. Moreover,pesticides cause pollution in enviroments and emergence of drug-resistant strains. Based on the development of sustainable agriculture, biological control is proposed as an alternative to reduce the use of chemical pesticides. One of the mechanisms of biological control is the production of secondary metabolites to kill or inhibit the pathogens.Paenibacillus polymyxa strain TP3 isolated previously from the phyllosphere of strawberry could effectively inhibit the growth of B. cinerea, and in greenhouse and field trials, strain TP3 could effectively reduce the disease severity of strawberry gray mold. Furthermore, strain TP3 could retard the infection of Colletotrichum gloeosporioides in greenhouse experiment and induce strawberry resistance against anthracnose, illustrating the potential of strain TP3 as a biocontrol agent. In this research, the anti-B. cinerea compounds produced by strain TP3 and its composition and structure were investigated. By a biochemical approach, antifungal compounds which could effectively inhibit the growth of B. cinerea were extracted and analyzed. High performance liquid chromatography and matrix-asisted laser desorption ionization-time of flight mass spectrometry were applied to identify the composition of the anti-B. cinerea compounds, which was presumed to be fusaricidins. Moreover, matrix-asisted laser desorption ionization-time of flight-imaging mass spectrometry showed that fusaricidins mainly distributed around the bacterial colony. Simultaneously, it also found that polymyxin E appeared at inhibition zone with apparent mass signals and could inhibit B. cinerea growth in vitro. Finally, composition and structure of fusaricidins produced by strain TP3 were analysed by liquid chromatography-tandem mass spectrometry and the results indicated an identity of fusaricidins as previously reported; however, the amino acid sequence of m/z 869 was different from the known fusaricidin of same m/z and the first amino acid of m/z 917 was different from that of known m/z 931, suggesting to be a novel fusaricidin member.