Selection Of Fusarium Oxysporum Inhibitory L. Plantarum Strains And Characterization Of Their Antifungal Activity

In this work,347Lactobacillus plantarum isolated from traditional fermented foods in Inner Mongolia, Xinjiang, Qinghai, Tibet, Gansu, Yunnan, Sichuan and Mongolian region were chosen. Their antifungal activity against Fusarium oxysporum was tested by assessing the mycelial growth rate. Moreover, the antifungal substances in the L. plantarum growth supernatants were preliminarily characterized.347Lactobacillus plantarum strains were cultured in by2%(V/V) in MRS medium for24hours at37℃. Growth supernatants were collected disgarding the bacterial cells after centrifugation. The inhibition of mycelial growth rate of Fusarium oxysporum was measured as the indicator for fungal inhibition. Three antibacterial L. plantarum strains, IMAU20063(inhibitory rate of47.77%), IMAU10140(inhibitory rate of46.66%), IMAU20118(inhibitory rate of47.57%), showing positive inhibitory effect and were selected. Supernatants from these3strains were further tested for their antifungal activities and properties, including concentration gradient test, lactic exclusion test, correlation between strain curve and inhibition rate of growth, thermal stability test, pH stability test, protease stability test and stability test. Results show that supernatant of these three L. plantarum strains were strongly thermal stable and the inhibitory rate remained over45%after50、60、70、80、100℃temperature treatment, and even increased after temperature treatment in80℃. For example, the supernatants of IMAU10140and IMAU20118had elevated antifungal activity after kept for20days in room temperature. Moreover, the antifungal materials were sensitive to protease treatment. The antifungal activity decreased by30%compared to the control after being treated with trypsin, proteinase K and neutral protease. Under acidic conditions (pH2-4), the antifungal activity was enhanced by as high as20.89%, and such activity was weakened or disappeared at neutral or alkaline conditions. However, based on our data, the antifungal activity was not attributed to lactic acid, as the addition of lactic acid surprisingly reduced the inhibition of the tested mold. The antifungal activity of the L. plantarum gradually increased with the growth and propagation of the bacteria, and reached a highest level of over50%when the strain was at the stationary phase (16-22h). Our results showed that the L. plantarum strains IMAU20063, IMAU10140and IMAU20118, can be explored as biological pesticides against Fusarium oxysporum.