Bt几丁质酶的基础表达及诱导合成的多态现象

Essential expression and inducible synthesis polymorphism of chitinase in Bacillus thuringiensis

多数微生物可以产生几丁质酶。一般认为几丁质酶基因表达受几丁质的诱导和葡萄糖抑制。但是苏云金芽胞杆菌Bacillus thuringiensis(简称Bt)几丁质酶的诱导表达方式是否与其他微生物相同,至今尚无定论。采用DNS法检测77株Bt在有或无诱导物培养基中的几丁质酶活力。研究了葡萄糖对4株不同表达类型菌株酶活力的影响,以及葡萄糖抑制与几丁质诱导之间的关系。研究发现在无几丁质诱导条件下,全部试验菌株都可以产生几丁质酶,保持一定量的基础表达,说明Bt能组成型合成几丁质酶,不需要诱导。添加诱导物之后,31株菌的酶活力没有任何变化,44株菌有不同程度的提高,但其中绝大部分诱导特性并不典型,酶活力提高不显著。许多Bt菌株几丁质酶表达兼具组成型和诱导型的特点。葡萄糖能够抑制几丁质的诱导作用,但是不能完全抑制Bt菌株几丁质酶的基础表达。比较组成型和诱导型菌株的几丁质酶基因chiA、chiB调节区域核苷酸序列,发现仅存在个别碱基的差异。

Chitinases were produced by a lot of microorganisms.Chitinase gene expression in most of the chitinase producing bacteria was inducible by chitin.Low levels of chitinase were observed in the presence of glucose.To date,however,the regulation of such chitinase gene in Bacillus thuringiensis had not been well studied.In this paper,all 77 Bacillus thuringiensis strains were grown in the medium with or without chitin.We measured quantitatively the chitinase activity of the cultures.Moreover,we investigated the suppressive effect of glucose on chitinase of 4 strains.Also we studied the relationship between chitin induction and glucose suppression on chitinase.This investigation demonstrated that all tested B.thuringiensis strains could produce chitinase without chitin.After induction,the chitinolytic activity of 31 tested strains had no obvious response to the inducer,whereas 44 stains increased in different degree.Among these strains,most of them did not markedly increase the levels of chitinase,and many stains simultaneously displayed the expression mode of inducible and constitutive.The glucose inhibited the inductive effect of chitin,but it could not inhibit the basal expression of chitinase.Two strains No.38 and No.75 belonged to different expression types.But we just found several different bases in the regulatory region of chitinase genes chiA and chiB from them.