LIN Zhen-ya, WU Qiong, SUN Rui-yan, CHEN Jie, LI Ya-qian
China Biotechnology. 2012, 32(10): 67-73.
Biological control of plant diseases is an effective method with the beneficial microorganisms or microbial metabolites against crop diseases. Streptomyces are already identified to produce a range of antibiotics including natamycin etc., which exhibit an excellent activities against fungal pathogens. Streptomyces lydicus A01 has been proved as a biocontrol microbe with antagonistic activity against Botrytis cinerea by producing natamycin, which degrading the cell membrane of fungal pathogens. Natamycin, a polyene macrolide antibiotic with broad-spectrum antifungal activity, has a stable and strong inhibitory activity against many plant pathogenic fungi, and is commonly used as antifungal agent. Chitinase can degrade chitin and could be used for resist many fungal pathogens. In A01-chit33CT, natamycin was produced to inhibit plant pathogens via destructing fungal cell membrane, while chit33 plays an important role in hydrolyzing the chitin component in fungal pathogen cell wall. The coordination effect of natamycin and chit33 may be improved significantly.
The optimal fermentation conditions for chitinase activity and natamycin produced in Streptomyces lydicus A01-chit33CT were studied. Firstly, the effect of different carbon and nitrogen sources on natamycin production and chitinase activities were investigated. The results showed that: glucose can promote natamycin production but inhibit the expression of chit33, so glucose and chitin powder were added into the fermentation medium with two-stage method to achieve collaborative expressions of both. The optimal medium compositions were as follow: chitin powder 10 g/L(after 4 days), glucose 40 g/L, soybean meal 30 g/L,soya peptone 10 g/L,CaCO3 5g/L,MgSO4·7H2O 0.5g/L,K2HPO4 0.5 g/L. Secondly, the cultural conditions were further to optimum as follows: initial pH 6.0, temperature 28℃, rotation speed 180 r/min. The highest natamycin production could reach 1.52 g/L and chitinase activity reach 990U/ml under the optimal fermentation conditions. Both levels improved by 1.95 and 2.27 times at post-optimazation compared to that of pre-optimization, respectively.
