A bromoperoxidase gene was cloned from Streptomyces aureofaciens Tu24 into Streptomyces lividans TK64 by using the promoter-probe vector pIJ486. Subcloning of DNA from the original, unstable clone allowed the gene to be localized to a 1.7-kilobase (kb) fragment of DNA. Southern blotting showed that the cloned 1.7-kb insert hybridized to a 4.3-kb fragment in an SstI digest of S. aureofaciens Tu24 total DNA. The 1.7-kb insert was shown to code for a protein with the electrophoretic properties of the subunits of the nonheme bromoperoxidase isolated from S. aureofaciens Tu24.-The protein produced by S. lividans TK64 transformed with pHM621, which contained an 8.0-kb insert, was shown to be identical to the S. aureofaciens Tu24 bromoperoxidase in terms of its electrophoretic mobility on denaturing and nondenaturing polyacrylamide gels and its NH2-terminal amino acid sequence. The bromoperoxidase was overproduced (up to 180 times) by S.lividans TK64 containing pHM621. Based on the heat stability of the S. aureofaciens Tu24 bromoperoxidase, a new and simple purification procedure with very high yields was developed.Streptomyces aureofaciens Tu24 produces the antibiotic 7-chlorotetracycline. The incorporation of chlorine during the biosynthesis of 7-chlorotetracycline is believed to be catalyzed by a chloroperoxidase (12). However, only a brominating enzyme, a bromoperoxidase, could be isolated from this strain (18). Bromoperoxidases have been isolated from other chlorometabolite-producing bacteria as well (16,17,20). The only bacterial chloroperoxidase known until now was detected in Pseudomonas pyrrocinia (2). This enzyme was detected as a bromoperoxidase by the monochlorodimedone assay developed by Hager et al. (2). Monochlorodimedone was not chlorinated by the chloroperoxidase from P. pyrrocinia; however, when indole was used as a substrate, it was chlorinated to 7-chloroindole (21), a substance which is known to be produced by P. pyrrocinia (8). Therefore, it was thought to be possible that the bromoperoxidase isolated from S. aureofaciens Tu24 could be a chloroperoxidase, too, but only if a more "natural" substrate than monochlorodimedone was used. To check this, large amounts of the enzyme are needed, and thus I decided to try to clone the bromoperoxidase gene of S. aureofaciens Tu24. This report describes the cloning of the S. aureofaciens Tu24 bromoperoxidase gene in S. lividans TK64.
MATERIALS AND METHODSBacterial strains and culture conditions. S. lividans TK64 and S. lividans TK24 containing the promoter-probe plasmid vector pIJ486 (19) were kindly supplied by D. A. Hopwood, Norwich, England, and S. aureofaciens Tu24 was provided by H. Zahner, Tubingen, Federal Republic of Germany (FRG). These strains were cultured on agar plates containing 2% (wt/vol) soybean flour and 2% (wt/vol) mannitol. This medium was also used as a liquid medium when cells were grown for the production of bromoperoxidase. Other media used were yeast extract-malt extract plus 34% (wt/vol) sucrose (YEME) (1); R2YE medium (14); P medium ...