Unit: Bacterial Genetics and Differentiation

Director: MAZODIER Philippe

We are interested in global control of morphological and physiological differentiation in Streptomycètes. There are many common elements in the regulation of these two types of differentiation. The Streptomycètes bacteria produce an incomparable range of secondary metabolites The determination of the sequence of the bacterial genomes reveals the presence of many antibiotic biosynthesis pathways not expressed and that even in the best studied species. We will try to characterize these modes of regulation and activate the production of these antibiotics.

Streptomyces spp. are Gram-positive, filamentous, soil bacteria. Streptomyces are remarkable in terms of the morphological and metabolic differentiation phenomena that they present. During the later stages of their development (aerial mycelium formation, sporulation). Streptomyces spp. generally synthesise a large number of very diverse secondary metabolites, the best known being antibiotics. Streptomyces and closely related genera produce more than 50 % of the 200 commercially available antibiotics and most of the 10,000 known antibiotics. Secondary metabolism also produces bioactive compounds that are used as antifungal, anti-parasitic, antiviral, anti-tumoural, or immunosuppressant agents or as insecticides or herbicides.

Study of the effect of the deregulation of ATP-dependent proteases Lon and Clp on morphological and physiological differentiations.

We showed that a mutation in the clpP1 gene prevented the formation of the aerial mycelium and to changes in the production of secondary metabolites. The ClpP protease which functions in partnership with ClpC and ClpX ATPase, is thus implied in the regulation of differentiation. The Clp system proved of a surprising complexity in Streptomyces with the characterization of five clpP genes and several control loops (auto- regulation and cross- regulation in cascade). The production of the proteases Lon and Clp is subjected to varied transcriptional (PopR, ClgR, HspR, σR) and post-translational regulations implying their proteolytic activities.

Study of the ssrA system in Streptomyces

We study the influence of the ssrA (tmRNA) system on genes expression in Streptomyces. We showed that it was not crucial. Nevertheless, we still think that one of the reasons of the inefficiency of the expression of certain genes could be due to the degradation of their product following the tagging of peptides in the course of synthesis by the SsrA system. Modification of ssrA might allow the expression of new antibiotic biosynthesis pathways in some Streptomyces.

Photo : Phenotypes of Streptomyces lividans wt and clpP1 mutant.

Growth of S. lividans wild type (right) and clpP1 mutant (left) Note the production of a red pigment (undecylprodigiosin), the " bald " phenotype, and a subtile peripheral morphological complementation in the mutant.

Keywords: ClpP, Lon, protease, degradation, Streptomyces, differentiation


Activity Reports 2004 - Institut Pasteur
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