| HNA3, a bacterium which was isolated from rhizosphere, could inhibit the growth of all tested plant pathogenic fungi. Culture filtrate of HNA3 could also inhibit the growth of plant pathogenic fungi in vitro. The HNA3 was identified as Bacillus amyloliquefaciens via morphological observation, analysis of 16S rDNA sequence and order of some unique genes.The tests of optimal fermentation conditions and antifungal activities demonstrated that BPY medium was the appropriate medium for HNA3’s culture growth, as well as for the production of bioactive antifungal compounds. HNA3 could grow well and produce antifungal compounds in the medium with pH values between 5.0 and 9.0. HNA3 cultured in 100mL BPY for 48h could produce the maximum biomass and antifungal compounds.We tested the stability of the antifungal compounds of HNA3’culture filtrates. The ability of HNA3 producing antifungal compounds would be genetic stable. The compounds were high stable towards temperature and UV, and were stess resistance towards pH values, organic solvents, some metal ions and anion ions. These results would be refered as its application in agriculture. Because the antifungal activity of culture filtrate didn’t decrease after being treated with proteinase K, we inferred that the antifungal compounds were not protein substance. The bioactive antifungal compounds could be separated from the culture filtrate through acid precipitation, and then the precipitate could be dissolved in methanol. We purified the bioactive compounds in methanol through HPLC.We found that HNA3’culture filtrate and dissolved precipitate possessed properties of surface active agents, which could display drop collapse and oil spreading. These properties demonstrated that the antifungal compounds would be biosurfactant substance. We analyzed the fragments of functional genes of three lipopeptides, and found that there was Iturin synthetase gene in the genome of HNA3. Then, we inferred that one of antifungal compound of HNA3 would be Iturin. The culture filtrate of HNA3 could inhibit the growth of fungal hypha, and the germination of fungal spore in vitro. We also observed that HNA3 fermentation broth biocontroled the disease rate of maize which was caused by Bipolaris maydis. |
