Submitted to: Environmental Health Perspectives
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 16, 2000
Publication Date: May 1, 2001
Interpretive Summary: Competitive inclusion is the competition process in which two organisms that can grow at the same location excludes the growth of the other, resulting in only one organism growing at that location. This process operates naturally, and it is usually the organisms who has some competitive edge over other that will survive. We have a species of bacterium, Bacillus mojavensis, that lives within plants (endophytic) producing a highly beneficial relationship with the plant. Fusarium moniliforme is parasitic fungus that also lives within plants, and at this same location: intercellular. The fungus produces several animal toxins in corn while it lives endophyticly with plants such as corn. On corn these toxins cause problems to horses, poultry, swine, and the fungus infested corn is associated with human esophageal cancer. This study demonstrates the production of these toxin early in the life of infected corn plants, and that under drought stress these toxins accumulate more. We then determined that the beneficial bacterium can out-compete with this fungus and prevent it from growing within the intercellular spaces of plants. The results is a reduction in the accumulation of mycotoxins inside the plants. We report in this work on the requirement of moisture for this association to occur and the reduction in toxin. The results of this study suggest that this endophytic bacterium can be used as a biological control for the fungus via the process of competitive exclusion.
Technical Abstract: Fusarium moniliforme Sheldon., a biological species of the mating populations within the Gibberella fujikuroi species complex, i.e. population A. Wineland, is an example of a fungal endophyte. During the biotrophic endophytic association with maize, as well as during saprophytic growth, F. moniliforme produces the fumonisins. The fungus is vertically and horizontally transmitted to the next generation of plants via clonal infection of seeds. The horizontal infection is the manner by which this fungus is contagiously spread and through which infection takes place from the outside that can be reduced by application of certain fungicides. The endophytic phase is vertically transmitted and this type infection is important as it is not affected by seed applications of fungicides, and it remains the reservoir from which infection and toxin biosynthesis in each generation of plants takes place. Thus, the vertical transmission of this fungus is equally important as horizontal transmission. A biological control system utilizing an endophytic bacterium, Bacillus subtilis, has been developed that shows great promise for the reduction in mycotoxin accumulation during the endophytic (vertical transmission) growth phase. Since this bacterium occupies the identical ecological niche within the plant, it is considered an ecological homologue to F. moniliforme, and the inhibitory mechanism, regardless of the mode of action, operates on the competitive exclusion principle. Also, an isolate of a species of the fungus Trichoderma shows promise in the post-harvest control of the growth and toxin accumulation from F. moniliforme in storage.