Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/10/2016
Publication Date: 10/4/2016
Citation: Blacutt, A.A., Mitchell, T.R., Bacon, C.W., Gold, S.E. 2016. Bacillus mojavensis RRC101 lipopeptides provoke physiological and metabolic changes in the course of antagonism against Fusarium verticillioides. Molecular Plant-Microbe Interactions. 29(9):713-723. doi:10.1094/MPMI-05-16-0093R.
Interpretive Summary: The fungus Fusarium verticillioides is a common fungus in corn and corn products. This fungus dwells within corn usually and such an association is call endophytic. As an endophyte, this fungus produces disease resulting usually in production of the fumonisins, which are toxic to human, livestock, and poultry. A bacterial endophyte Bacillus mojavensis has been shown to reduce the accumulation of these fumonisins, and has some biocontrol potential. As results of determining the sequence of this bacterium, another surfactant was identified and studied. It was determined that this new surfactant, fengycin, was very toxic to F. verticillioides as shown by microscopic examinations. It was also determined that the fungus responded to fengycin by the production of higher amounts of fumonisins than cultures without fengycin suggesting that antibiotic and toxin production are components of a complex biochemical interaction, one toxic and one beneficial. Studies of each might provide a clue as to how the other might be control and this hypothesis is being investigated.
Technical Abstract: The mycotoxigenic pathogen Fusarium verticillioides threatens the quality and utility of maize across industrial and agricultural purposes. Chemical control is complicated by the intimate endophytic lifestyle of the pathogen with its host. Bacillus mojavensis RRC 101, a maize10 endophytic bacterium, has been observed to reduce F. verticillioides disease severity and fumonisin accumulation when co-inoculated to maize. Genome sequencing and annotation identified a number of biocontrol-relevant pathways in RRC 101. Biochemical assays confirmed the presence and activity of surfactin and fengycin type lipopeptides, with fengycins responsible for antifungal activity against F. verticillioides. This antagonism manifests as inhibition of filamentous growth, with microscopy revealing hyphal distortions, vacuolization, and lysis. F. verticillioides secondary metabolism also responds to antagonism, with lipopeptide challenge inducing greater fumonisin production and, in the case of fengycins, eliciting pigment accumulation at sites of inhibition. Together these data suggest that antibiotic and toxin production are components of a complex biochemical interaction among maize endophytes, one pathogenic and one beneficial.