Regulation of multidrug efflux pumps by TetR family transcriptional repressor negatively affects secondary metabolism inStreptomyces coelicolorA3(2)

Abstract

ABSTRACTStreptomycesspp. are well-known producers of bioactive secondary metabolites (SMs) that serve as pharmaceutical agents. In addition to their ability to produce SMs,Streptomycesspp. have evolved diverse membrane transport systems to protect cells against antibiotics produced by itself or other microorganisms. We previously screened mutants ofStreptomyces coelicolorthat show a phenotype of reduced undecylprodigiosin (RED) production in a combined-culture withTsukamurella pulmonis. Here, we identified a point mutation, which reduced RED production, by performing genome resequencing and genetic complementation. We found that inactivation of thesco1718gene encoding the TetR family transcriptional regulator (TFR) produced a deficient phenotype for several SMs inStreptomyces coelicolorA3(2). Electrophoretic mobility shift assay and quantitative reverse transcription-PCR experiments demonstrated that SCO1718 repressed the expression of adjacent two-component ATP-binding cassette (ABC) transporter genes (sco1719-20) by binding to the operator sequence in the 5′-UTR. Notably, the Δsco1718mutant showed increased resistance to several antibiotics of other actinomycete origin. In the genome ofS. coelicolorA3(2), two other sets of TFR and two-component ABC transporter genes (sco4358-4360andsco5384-5382) were found, which had similar effects on the phenotype for both secondary metabolism and antibiotic resistance. Our results imply the switching of cell metabolism to direct offence (antibiotic production) or defense (efflux pump activation) using costly and limited quantities of cell energy sources (e.g., ATP) in the soil ecosystem.IMPORTANCEThe bacterial metabolic potential to synthesize diverse secondary metabolites (SMs) in the environment has been revealed by recent (meta-)genomics of both unculturable and culturable bacteria. These studies imply that bacteria are continuously exposed to harmful chemical compounds in the environment.Streptomycesspp. contain antibiotic efflux pumps and SM biosynthetic gene clusters. However, the mechanism by which soil bacteria, includingStreptomyces, survive against toxic compounds in the environment remains unclear. Here, we identified three sets of TFR-ABC transporter genes inStreptomyces coelicolorA3(2). We found that each TFR controlled the expression of a respective ABC transporter, and the expression of all ABC transporters negatively impacted SM production and increased antibiotic resistance. Notably, bioinformatic analysis indicated that these TFR-ABC transporter gene sets are highly conserved and widely distributed in the genome ofStreptomycesspecies, indicating the importance of systematic regulation that directs antibiotic production and xenobiotic excretion.