Submitted to: Journal of Food Protection
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/10/2007
Publication Date: 7/1/2007
Citation: Palumbo, J.D., O Keeffe, T.L., Abbas, H.K. 2007. Isolation of maize soil and rhizosphere bacteria with antagonistic activity against Aspergillus flavus and Fusarium verticillioides. Journal of Food Protection. 70(7):1615-1621. Interpretive Summary: Bacteria from cornfield soil and corn roots were tested to find individual bacteria that could limit the growth of the fungi Aspergillus flavus and Fusarium verticillioides, two mycotoxin-producing corn pathogens. Tests in liquid and agar media identified 221 bacterial strains that could inhibit both fungi. Strains were identified using genetic and biochemical tests, and tests to show whether they were capable of degrading fungal cell wall components were used to further distinguish strains of the same species. Twenty strains were selected to demonstrate their effects on the amount of fungal growth when each fungus and bacterial strain were grown together in different liquid medium. Two strains of Pseudomonas were identified that consistently limited growth of both fungi in the laboratory, suggesting their potential for use as biocontrol agents on corn.
Technical Abstract: Bacterial isolates from Mississippi maize field soil and maize rhizosphere samples were evaluated for their potential as biological control agents against Aspergillus flavus and Fusarium verticillioides. Isolated strains were screened for antagonistic activities in liquid co-culture against A. flavus and on agar media against A. flavus and F. verticillioides. We identified 221 strains that inhibited growth of both fungi. These bacteria were further differentiated by their production of extracellular chitin- and yeast cell wall-hydrolyzing enzyme activities, as well as production of antifungal metabolites. Based on molecular and nutritional identification of the bacterial strains, the most prevalent genera isolated from rhizosphere samples were Burkholderia and Pseudomonas, while the most prevalent genera isolated from non-rhizosphere soil were Pseudomonas and Bacillus. Less prevalent genera included Stenotrophomonas, Agrobacterium, Variovorax, Wautersia, and several genera of coryneform and enteric bacteria. In quantitative co-culture assays, strains of P. chlororaphis and P. fluorescens consistently inhibited growth of A. flavus and F. verticillioides in different media. These results demonstrate the potential for developing individual biocontrol agents for simultaneous control of both mycotoxigenic fungi.