Streptomycetes are saprophytic bacteria that grow on complex polysaccharides, such as cellulose, starch, chitin and chitosan. For the monomeric building blocks glucose, maltose and N-acetylglucosamine (GlcNAc), the metabolic pathways are well documented, but that of glucosamine (GlcN) is largely unknown. Streptomyces nagB mutants, which lack glucosamine-6-phosphate deaminase activity, fail to grow in the presence of high concentrations of GlcN. Here we report that mutations in the gene for the ROK-family transcriptional regulator RokL6 relieve the toxicity of GlcN in nagB mutants, as a result of elevated expression of the Major Facilitator Superfamily (MFS) exporter SCO1448. Systems-wide analysis using RNA sequencing, ChIP-Seq, EMSAs, 5’RACE, bioinformatics and genetics revealed that RokL6 is an autoregulator that represses transcription of SCO1448 by binding to overlapping promoters in the rokL6-SCO1448 intergenic region. RokL6-independent expression of SCO1448 fully relieved toxicity of GlcN to nagB mutants. Taken together, our data show a novel system of RokL6 as a regulator that controls the expression of the MFS transporter SCO1448, which in turn protects cells against GlcN toxicity, most likely by exporting toxic metabolites out of the cell.

Systems-wide analysis of the ROK-family regulatory gene rokL6 and the control of aminosugar toxicity in Streptomyces coelicolor