Submitted to: Aflatoxin Elimination Workshop Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 10/3/2005
Publication Date: 7/1/2006
Citation: Bacon, C.W., Hinton, D.M. 2006. Fusaric acid, a fusarium verticillioidies miasma to bacillus mojavensis, a biological control bacterial endophyte. Aflatoxin Elimination Workshop Proceedings. p. 61.
Technical Abstract: Antagonisms among microorganisms are strategies that maintain both inter- and intra- specific competition, which is particularly important among those microorganisms that are ecological homologues. Fusarium verticillioides is systemically localized in corn and is prevalent in the roots as opposed to the shoot axis of corn, and is best described as a root endophyte. During its early biotrophic phase of its association with corn, hyphae dwell within the intercellular spaces of corn. A biocontrol bacterium, Bacillus mojavensis, is patented as an endophytic biocontrol agent of plant diseases. The intention is to replace the fungus with this endophytic bacterium as a management strategy which operates under the broad mechanism of competitive exclusion. Under greenhouse conditions, corn infected with the bacterium shows increased growth and rooting, seedling vigor and disease resistance. Also under these conditions, fumonisin concentration in corn is reduced by 60% in the presence of the fungus, and fungus infection, expressed as CFU/gram of plant tissue, is also reduced. However, use of this bacterium under field conditions and contrary to greenhouse conditions, F. verticillioides is superior in colonizing corn plants pre-inoculated with the bacterium. Of the many toxins produced by F. verticillioides, fusaric acid might be involved in this effect. Fusaric acid (5-butylpicolinic acid), first discovered during the laboratory culture of F. heterosporum, was one of the first fungal metabolites implicated in the pathogenesis of wilt symptoms of plants. In addition to this role in plant pathogenesis, fusaric acid is mildly toxic to mice, and has several important pharmacological properties, and perhaps its major importance in animal toxicity may be synergistic interactions with other naturally co-occurring mycotoxins. It was determined that fusaric acid accounted for the reduction in bacterial growth and resulting decrease in biocontrol activity. Fusaric acid supplied to cultures of the bacterium, at a concentration as low as 22 uM, accounted for a 41% reduction in growth of the bacterium. It is also toxic to this bacterium. Fusaric acidless mutants of F. verticillioides were ineffective in colonizing B. mojavensis-infected maize, suggesting that fusaric acid is one important defense mechanism for the fungus. The results indicate that the biocontrol bacterium must be modified to resist fusaric acid before its use under field conditions. Two fusaric acid tolerant bacterial mutants have been developed that are endophytic and antagonistic to the fungus. These mutants will form the basis of subsequent field testing for the control of F. verticillioides.