Stress-induced antibiotic production in bacteria

Streptomyces bacteria produce a variety of biologically active natural products (secondary metabolites), some of which are used as antibiotics, anticancer and immunosuppressive agents in human therapy. These bacteria typically produce 3-5 different compounds under laboratory conditions. As was recently shown via genome sequencing, their true capacity for synthesizing various natural products is far greater, but many genes governing biosynthesis of natural products remain silent. Stress conditions are known to activate some of these silent genes, leading to the production of previously undetected compounds, while molecular mechanisms behind this phenomenon are poorly understood. In the proposed StrepStress project we intend to identify and characterize regulatory network that activates antibiotic biosynthesis in response to environmental stress using bacterium Streptomyces venezuelae as a model. S. venezuelae harbours silent genes for the biosynthesis of antibiotic jadomycin (Jad), which are not expressed under standard laboratory conditions. However, addition of 6% ethanol (EtOH) within the first 6-17 hours of cultivation induces Jad biosynthesis. It is currently not known what kind of intracellular signals are generated by EtOH shock, and how these signals are transduced to activate Jad biosynthesis. To investigate this, we will apply state-of-the-art technologies including transcriptomics, metabolomics and phenotypic arrays to build a model of stress- induced signal transduction leading to activation of antibiotic biosynthesis. The model will be experimentally verified via construction and testing of recombinant bacteria with perturbed regulatory network. This project will provide important new insights into the global regulation of secondary metabolism in bacteria and may pave the way to the discovery of new antibiotics.

The StrepStress project was designed to investigate details of the regulatory network controlling production of antibiotics and other bioactive natural products of medicinal importance in bacteria. In particular, we were interested in finding out how the environmental factors affect production of these natural products. Many bacteria have hidden genetic potential for antibiotic production, which is often not realized in the laboratory. Hence, the discovery of new bioactive natural products is hampered, and many potentially useful drugs can be missed by researchers. The overall aim was to reveal critical bacterial genes involved in the process of activation of antibiotic production which can be manipulated to increase the yield of particular antibiotics, hence making the industrial processes more sustainable and profitable. This aim was addressed with the most advanced interdisciplinary approaches, which included global analyses of gene expression in antibiotic-producing bacterium subjected to environmental stress. The pattern of gene expression was then correlated with the analysis of production of antibiotics and other natural products. Upon careful inspection and correlation of obtained megadata, we used genetic engineering to manipulate three genes identified as most important members of regulatory network related to antibiotic biosynthesis. Genetically engineered strains were shown to produce greatly enhanced amounts of natural products. Some, for example antibiotic chloramphenicol, were overproduced ca 1700-fold. Most interestingly, each of the manipulated genes had a specific effect on the production of one or more natural products, showing that we can specifically enhance production of targeted compounds. Since the genes we manipulated are conserved in many antibiotic-producing bacteria, we believe that our discovery can be applied to significantly enhance industrial production of medically important antibiotics and anti-cancer drugs. Considering the looming antibiotic resistance crisis, we believe that our results may contribute to solving problems of new antibiotic discovery.