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测定苏云金芽胞杆菌(Bacillus thuringiensis,简称Bt)407及其突变株407ΔplcR、407ΔinhA2、407ΔmpbE、407ΔsigmaE和407ΔsigmaK对数生长期与稳定期的拐点时间t0,测定不同时间点发酵液上清中的总铬(Cr)和Cr(Ⅵ)的浓度,并分析Bt 407基因组的抗性相关基因,进而初步构建Bt解毒Cr(Ⅵ)模式图.结果表明,plcR、inhA2、mpbE、sigmaK负调控Bt 407解毒Cr(Ⅵ)的能力并主要影响Cr(Ⅵ)还原过程,sigmaE不影响对Cr(Ⅵ)的解毒过程.利用Bt 407基因组序列分析得到与Cr(Ⅵ)抗性相关基因NADPH偶氮还原酶基因azoR、外排蛋白基因efx和chrA.推测Bt 407对Cr(Ⅵ)抗性机制可能为:azoR编码NADPH偶氮还原酶将细胞内Cr(Ⅵ)还原为Cr(Ⅲ),Cr(Ⅲ)再通过ChrA或与azoR共表达的外排蛋白Efx从细胞质中排出,这一还原过程直接/间接受到plcR、inhA2、mpbE、sigmaK等调控基因的负调控.因此,Bt 407对Cr(Ⅵ)的解毒机制是由azoR、efx、chrA等主效基因与plcR、inhA2、mpbE、sigmaK等调控基因共同作用的复杂网络.
The time of inflection point (T0) of Bacillus thuringiensis 407 and its mutants 407ΔplcR, 407ΔinhA2, 407ΔmpbE, 407ΔsigmaE and 407ΔsigmaK in logarithmic growth phase and stationary phase were determined. Total chromium Cr (Ⅵ), Cr (Ⅵ) and Cr (Ⅵ), and analyzed the resistance related genes of Bt 407 genome to further establish the pattern diagram of Bt detoxification Cr (Ⅵ). The results showed that plcR, inhA2, mpbE and sigmaK negatively regulated Bt 407 detoxification of Cr Ⅵ) and mainly affected the reduction process of Cr (Ⅵ), while sigmaE did not affect the detoxification of Cr (Ⅵ) .By using the Bt 407 genomic sequence analysis, we obtained the results of azoR, The extrinsic protein genes efx and chrA were presumed to be resistant to Cr (Ⅵ) by azoR encoding NADPH azo reductase, which reduced Cr (Ⅵ) to Cr (Ⅲ), Cr (Ⅲ) Or the efflux protein Efx coexpressed with azoR is excreted from the cytoplasm.This process of reduction is directly / indirectly regulated by the regulatory genes plcR, inhA2, mpbE, sigmaK, etc. Therefore, the mechanism of detoxification of Cr (VI) by Bt 407 is By azoR, efx, chrA other major gene and plcR, inh A2, mpbE, sigmaK and other regulatory genes play a complex network.