Cyclic di-AMP metabolism and functions in Streptomyces

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The Gram-positive soil bacteria streptomycetes belong to natures most competent natural product factories and are an important source of diverse antibiotics and other bioactive molecules for medical, veterinary and agricultural use. The production of these secondary metabolites is temporally and genetically coordinated with a complex developmental life cycle involving growth as vegetative mycelium of branching hyphae and dispersion via spores formed on specialized reproductive structures called aerial hyphae. We have recently shown that in Streptomyces venezuelae the diadenylate cyclase (DAC) domain-containing protein DisA produces the nucleotide second messenger cyclic di-AMP which controls the levels of the cell wall lytic enzyme RpfA by binding to a riboswitch in the 5-untranslated leader region (UTR) of the rpfA gene. However, our knowledge about the biosynthesis, turnover and functions of c-di-AMP in the physiology of streptomycetes is still very limited. The aim of the proposed work within the SPP 1879 is to analyse and characterise in molecular detail the roles of DisA and c-di-AMP in S. venezuelae. We will determine the conditions under which DisA is expressed and active and define how this protein and c-di-AMP contribute to differentiation and stress survival strategies employed by Streptomyces spp. Since streptomycetes do not contain any of the already characterised c-di-AMP-binding proteins, we will perform a global screen for c-di-AMP effector proteins, which will allow us to identify a potentially novel type of c-di-AMP-degrading phosphodiesterases and a new class of effectors. Further, in our previous, unpublished studies we found, that S. venezuelae produces an up to now uncharacterised cyclic di-nucleotide. Detailed analysis and characterisation of this compound will lead to the discovery of a novel type of nucleotide-based second messengers in bacteria. Altogether, this work will greatly improve our understanding of the physiology and stress survival mechanisms in Streptomyces spp. and contribute to a better knowledge of c-di-AMP signalling in a new physiological context involving multicellular differentiation and secondary metabolite production.