CHARACTERIZATION OF THE DESULFURIZATION GENES FROM RHODOCOCCUS SP STRAIN IGTS8

Rhodococcus sp. strain IGTS8 possesses an enzymatic pathway that can r emove covalenty bound sulfur from dibenzothiophene (DBT) without break ing carbon-carbon bonds. The DNA sequence of a 4.0-kb BstBI-BsiWI frag ment that carries the genes for this pathway was determined. Frameshif t and deletion mutations established that three open reading frames we re required for DBT desulfurization, and the genes were designated sox ABC (for sulfur oxidation). Each sox gene was subcloned independently and expressed in Escherichia coli MZ1 under control of the inducible l ambda p(L) promoter with a lambda cII ribosomal binding site. SoxC is an similar to-45-kDa protein that oxidizes DBT to DBT-5,5'-dioxide. So xA is an -similar to-50-kDa protein responsible for metabolizing DBT-5 ,5'-dioxide to an unidentified intermediate. SoxB is an similar to-40- kDa protein that, together with the SoxA protein, completes the desulf urization of DBT-5,5'-dioxide to 2-hydroxybiphenyl. Protein sequence c omparisons revealed that the predicted SoxC protein is similar to memb ers of the acyl coenzyme A dehydrogenase family but that the SoxA and SoxB proteins have no significant identities to other known proteins. The sox genes are plasmidborne and appear to be expressed as an operon in Rhodococcus sp. strain IGTS8 and in E. coli.