|QUECINE, MARIA - Universidad De Sao Paulo
|GOEBEL, NEAL - Oregon State University
|ZABRISKIE, T - Oregon State University
Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/11/2015
Publication Date: 3/1/2016
Citation: Quecine, M.C., Kidarsa, T.A., Goebel, N.C., Shaffer, B.T., Henkels, M.D., Zabriskie, T.M., Loper, J.E. 2016. An inter-species signaling system mediated by fusaric acid has parallel effects on antifungal metabolite production by Pseudomonas protegens Pf-5 and antibiosis of Fusarium spp. Applied and Environmental Microbiology. 82:1372-1382.
Interpretive Summary: Biological control provides a promising strategy for managing plant diseases, but has not yet been utilized widely in agriculture due, in part, to unexplained variation in its success in managing disease. Our research goals are to identify sources of variation in biological control, and devise ways to make it more reliable. We focus on Pseudomonas protegens Pf-5, a bacterium that occurs naturally on plant surfaces such as leaves and roots and produces many antifungal compounds that suppress plant pathogenic fungi. The results of this paper demonstrated the importance of three compounds, rhizoxin, pyrrolnitrin and DAPG, in suppression of plant pathogenic Fusarium spp. by Pf-5. Fusarium spp. are important fungal plant pathogens of many crop plants, and some species of Fusarium produce toxins such as fusaric acid. We showed that fusaric acid influenced antifungal metabolite production and antibiosis by Pf-5. These results add to the information about factors influencing gene expression in plant-associated Pseudomonas spp. , which can assist scientists in formulated more consistent biological control strategies for use in agriculture.
Technical Abstract: Pseudomonas protegens strain Pf-5 is a rhizosphere bacterium that acts as a biocontrol agent of soilborne plant diseases, and produces at least seven different secondary metabolites with antifungal properties. We derived site-directed mutants of Pf-5 with single and multiple mutations in the biosynthetic gene clusters for all seven antifungal metabolites: 2,4-diacetylphoroglucinol (DAPG), pyrrolnitrin, pyoluteorin, hydrogen cyanide, rhizoxin, orfamide A and toxoflavin. These mutants were tested for suppression of the pathogens Fusarium verticillioides and F. oxysporum f. sp. pisi, and rhizoxin, pyrrolnitrin and DAPG were found to be primarily responsible for fungal antagonism by Pf-5 on several culture media. Previously, other workers showed that the mycotoxin fusaric acid, which is produced by many Fusarium species including F. verticillioides, inhibited the production of DAPG by Pseudomonas spp. In this study, amendment of culture media with fusaric acid decreased DAPG production, increased pyoluteorin and rhizoxin production, and had no consistent influence on pyrrolnitrin or orfamide A production by Pf-5. Fusaric acid had parallel effects on the transcription of biosynthetic genes, assessed using RT-qPCR, indicating that the mycotoxin influenced antibiotic production by Pf-5 at the transcriptional level. Addition of fusaric acid to the culture medium reduced antibiosis of F. verticillioides by Pf-5 and derivative strains that produce DAPG, but had no effect on antibiosis by Pf-5 derivatives that suppressed F. verticillioides due to pyrrolnitrin or rhizoxin production. Our results demonstrated the importance of three compounds, rhizoxin, pyrrolnitrin and DAPG, in suppression of Fusarium spp. by Pf-5, and confirmed that an inter-species signaling system mediated by fusaric acid had parallel effects on antifungal metabolite production and antibiosis by the bacterial biological control organism.