Burkholderia ambifaria T16, a fusaric acid degrading rhizobacterium, produces antifungal metabolites active against Fusarium spp.

ROBERTS IN; MONTECCHIA MS; OTTAVIANO C; RUIZ JA

La Falda

Workshop; II Latin American PGPR Workshop II Taller latinoamericano sobre rizobacterias promotoras del desarrollo vegetal; 2014

The genus Fusarium includes many species that cause plant diseases. Some of the pathogenic species produce a variety of mycotoxins, among them fusaric acid (FA), a toxin contributing to pathogenesis in several crops. We have previously reported the isolation of a native bacterium from the rhizosphere of barley. This isolate, designated T16, showed the interesting ability to use FA as sole carbon and energy source and the capacity to suppress the toxic effect of FA on barley seedlings. Here, the taxonomic identification of the bacterial isolate is reported. We also analyzed the antifungal activity of the bacterial isolate against several phytopathogenic species of Fusarium and its ability to solubilize different forms of insoluble phosphate. Taxonomic identification of isolate T16 was achieved through sequence analysis of 16S rRNA, recA and gyrB genes. Antifungal activity was determined by dual culture experiments and by testing the effect of the cell free supernatant from cultures of B. ambifaria T16 grown to stationary phase on Fusarium spp. growth. The ability of B. ambifaria T16 to antagonize growth of F. oxysporum, F. graminearum, F. solani, and Fusarium sp. was evaluated. Ability of B. ambifaria T16 to solubilize Ca3(PO4)2, FePO4 or AlPO4 was assayed in plates. Based on the phylogenetic analyses of 16S rRNA, recA and gyrB genes sequences, strain T16 was identified as Burkholderia ambifaria. In dual growth assays, B. ambifaria T16 was able to inhibit the micelial growth of the six Fusarium isolates tested, ranging from 63% to 29% growth reduction. The cell free supernatant also showed the capacity to inhibit fungal growth when tested at different final concentrations (10, 25 and 50%) being growth inhibition higher with increasing concentration of cell free supernatant. The percentages of inhibition obtained ranged from 39% (with 10% supernatant) to 73% (with 50% supernatant). Finally, B. ambifaria T16 was able to solubilize insoluble Ca3(PO4)2. However, phosphate solubilizing activity was not evident in FePO4 or AlPO4 containing media. We identified a bacterium isolated from the rhizosphere of barley, interesting because of its FA detoxifying activity, as B. ambifaria. This bacterial species has been reported as a common inhabitant of the rhizosphere of several crops. B. ambifaria T16 was also able to inhibit the growth of several phytopathogenic species of the genus Fusarium. This antagonism against Fusarium spp. is probably due to the production of extracellular metabolites, as demonstrated by the inhibition of fungal growth by cell free supernatants. B. ambifaria T16 also showed the ability to solubilize phosphate, a limiting nutrient in soil. Overall, these results show that B. ambifaria T16 possesses several characteristics with potential biotechnological applications in the biocontrol of Fusarium spp. and biological detoxification of FA, which deserve deeper research.