Genetic Analysis of Global Regulation of Streptomyces Antibiotics

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Streptomycetes, a group of filamentous soil bacteria, possess two characteristics that make them attractive prokaryotes for study: they develop into complex, multicellular, differentiated colonies and they produce a vast array of secondary metabolites, many of which are useful as antibiotics. Antibiotic production is usually coupled to morphological differentiation, beginning at the transition between vegetative growth and production of pre-spore differentiated hyphae. The long-term goal of this research is to discover the genes that regulate antibiotic synthesis, to understand how they function, and to determine their functional relationships in the regulatory network controlling antibiotic gene expression. The immediate objectives of this research are focussed on three recently-discovered genetic elements: absA, absB and absC. The mechanism by which the AbsA2 response regulator of the absA-encoded signal transduction system exerts global negative control over antibiotic gene expression will be determined using genetic, molecular genetic, and biochemical experiments to: a) determine the antibiotic promoters that are directly regulated by AbsA2; and b) characterize repressor activity by AbsA2. Aspects of the mechanism by which the absB-encoded RNaseIII homolog regulates antibiotics will be determined using suppressor analysis to identify elements of the pathway through which absB regulates antibiotics and by evaluation of the role of RNaseIII catalytic activity in antibiotic regulation. Aspects of the mechanism by which the absC operon regulates antibiotic gene expression will be determined by defining how a 120 nt sequence of the absC locus, mia, exerts multi-copy inhibition of antibiotic gene expression, especially evaluating the strong prediction that it titrates a regulatory factor. The results of this research promise to elucidate aspects of the regulatory program controlling streptomycete antibiotic synthesis, to provide insights into how antibiotic production might be rationally manipulated, and to expand our understanding of microbial multicellular differentiation.