Agarase overproduction in Streptomyces lividans

The gene dagA encoding agarase in Streptomyces coelicolor was cloned in the multicopy plasmid pIJ486 generating plasmid pAGAs5. Plasmid pAGAs5 and pIJ486 were propagated in S. lividans TK21 to obtain S. lividans TK21(pAGAs5) and its isogenic strain S. lividans TK21(pIJ486). Transcriptional profiling of the bacterium that overproduces agarase mainly resulted in the downregulation of the genes involved in the biogenesis and function of ribosomes, together with the downregulation of the genes involved in nitrogen, aminoacids, purine/pyrimidine and central carbon metabolism as well as ABC transporters, redox processes and fatty acids biosynthesis. The number of genes upregulated in the agarase overproducer strain is lower than in the downregulated ones. Almost 50% of the dowregulated genes have been described as forming part of the stringent response in streptomycetes. Therefore, the overproduction of agarase may lead to a condition of nutrient depletion that triggers the stringent response. All microarray analyses were performed with RNA samples obtained from three independent cultures grown under identical conditions. The cDNA obtained from each RNA preparation of the agarase overproducer strain was hybridised with the cDNA obtained from the equivalent RNA preparation of the isogenic strain (S. lividans TK21 [pIJ486]).