Resistance Genes of Aminocoumarin Producers: Two Type II Topoisomerase Genes Confer Resistance against Coumermycin A 1 and Clorobiocin

Abstract

ABSTRACT The aminocoumarin resistance genes of the biosynthetic gene clusters of novobiocin, coumermycin A 1 , and clorobiocin were investigated. All three clusters contained a gyrB R resistance gene, coding for a gyrase B subunit. Unexpectedly, the clorobiocin and the coumermycin A 1 clusters were found to contain an additional, similar gene, named parY R . Its predicted gene product showed sequence similarity with the B subunit of type II topoisomerases. Expression of gyrB R and likewise of parY R in Streptomyces lividans TK24 resulted in resistance against novobiocin and coumermycin A 1 , suggesting that both gene products are able to function as aminocoumarin-resistant B subunits of gyrase. Southern hybridization experiments showed that the genome of all three antibiotic producers and of Streptomyces coelicolor contained two additional genes which hybridized with either gyrB R or parY R and which may code for aminocoumarin-sensitive GyrB and ParY proteins. Two putative transporter genes, novA and couR5 , were found in the novobiocin and the coumermycin A 1 cluster, respectively. Expression of these genes in S. lividans TK24 resulted in moderate levels of resistance against novobiocin and coumermycin A 1 , suggesting that these genes may be involved in antibiotic transport.