Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/15/2007
Publication Date: 9/25/2007
Citation: Bacon, C.W., Hinton, D.M., Glenn, A.E., Macias, F.A., Marin, D. 2007. Interactions of Bacillus mojavensis and Fusarium verticillioides with a benzoxazolinone (BOA) and its transformation product, APO. Journal of Chemical Ecology. 33:1885-1897. Interpretive Summary: Corn contains a natural class of antibiotic compounds, the benzoxazolinones. These substances appear within the corn seedling within 6 days of germination and serve the purpose of protecting the corn from insects and fungal pathogens. However, one toxic fungus, Fusarium verticillioides, is tolerant to these benzoxazolinones since it can detoxify these and remain a problem in corn. The fungus produces fumonisin toxins that cause problems to humans, livestock and poultry consuming F. verticillioides contaminated corn. A biocontrol bacterium, Bacillus mojavensis, is being used to prevent the growth of this F. verticillioides. Experiments were conducted to determine if the benzoxazolinones were toxic to this bacterium, and further to see if there were any interactive effects of the fungus with these compounds on the growth of the bacterium. The results indicate that indeed the bacterium is also tolerant to the benzoxazolinones, and can prevent the fungus from detoxifying these antimicrobials, causing the accumulation of a more toxic class of benzoxazolinones that now kills the fungus. Thus, the conclusion is that the bacterium and the benzoxazolinones should prove even more effective in preventing corn from being colonized by F. verticillioides and that the production of the fumonisin should be reduced.
Technical Abstract: The benzoxazolinones, specifically benzoxazolin-2(3H)-one (BOA), are important transformation products of cyclic hydroxamic acids that serve as allelochemicals, which provide resistance to maize from pathogenic bacteria and fungi, and insects. However, several maize pathogens such as Fusarium verticillioides are capable of detoxifying the benzoxazolinones, producing less toxic N-(2-hydroxyphenyl) malonamic acid (HPMA) and 2-acetamidophenol (HPAA). Since biocontrol strategies utilizing a species of endophytic bacterium, Bacillus mojavensis, are considered efficacious as a control of this Fusarium species, the in vitro transformation and effects of BOA on growth of this bacterium is examined relative to its interaction with strains of F. verticillioides. The results showed that a red pigments is produced and accumulate only on BOA amended media when wild type and mutant strains of F. verticillioides are cultured in the presence of the bacterium. The red pigment was identified as 2-amino-3H-phenoxazin-3-one (APO), which is a toxic and stable product. The results indicate that the bacterium interacts with the intermediate product of these allelochemicals, possibly inhibiting the fungal gene responsible for the decomposition of AP to HPMA, resulting in accumulation of APO, which is very toxic to F. verticillioides. Thus, an enhanced biocontrol is suggestive by this in vitro study.