Elucidation and Application of Enzyme System and Genes Involved in Microbial Desulfurization

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The mesophilic desulfurizing bacterium, Rhodococcus erythropolis D-1, has an ability of desulfurizing dibenzothiophene (DBT), the model compound for the microbial desulfurization, to form 2-hydoxybiphenyl (2-HBP). The enzyme system of DBT desulfurization consists of DszC, DszA, and DszB attacking DBT and its metabolites. Moreover, flavin reductase (FR) is essential for the activities of DszC and DszA. In this study, FR and DszB were studied.FR was purified from R. erythropolis D-1 to homogeneity. The enzyme was tetramer, and the molecular mass of subunit was 22kDa. The enzyme had a strict substrate specificity and showed a high thermostability. The recombinant Escherichia coli strain overproduced FR, and the specific activity increased higher 275 times than the wild strain.At first, the purification of DszB was tried form R. erythropolis D-1. But the pure enzyme could not be prepared because of the instability. Next, the recombinant strain was constructed. Because the inclusion body was formed when the expression vector was used, the DszB gene was coexpressed with the molecular chaperon genes, groELgroES. The purified enzyme was prepared from the recombinant E. coli. It was demonstrated that DszB cleaved the C-S bond of aromatic compound without any other proteinic component and cofactor.