Screening and identification of chitinase-producing bacterium and its antagonistic activity against Fusarium oxysporum f. sp. cubense.

In order to screen chitinase-producing bacteria which could inhibit the growth of pathogen, chitinase-producing strains were isolated by double screen with the chitin and pathogen cell wall as sole carbon, and then, by dual culture, an antagonistic bacillus against Fusarium oxysporum f. sp. cubense was isolated from chitinase-producing strains. Based on morphological characteristics and the homology analysis of 16S rDNA sequence, the strain was identified as Bacillus subtilis and was named XW-2. In order to study the effects of environmental factors on the antagonistic substance activity of fermentation filtrate, the culture conditions of XW-2, such as temperature, pH and medium were studied. The results showed that an initial range of pH 7.0 to 8.0 in the liquid culture and a temperature range of 31 to 34 ℃ were most favorable for the production of antagonistic substance. It was also indicated that the chitin was better than cytoderm for the induction of antagonistic activity. The study showed that the mycelium growth of fungi was inhibited seriously with the fermentation filtrate, and microscope observation of antagonistic action revealed that the fungi hypha were constricted, dissolved, and had an inflated tip, mycelium was deformed and fractured to small segments.