Highlights of Streptomyces genetics.

Sixty years ago, the actinomycetes, which include members of the genus Streptomyces, with their bacterial cellular dimensions but a mycelial growth habit like fungi, were generally regarded as a possible intermediate group, and virtually nothing was known about their genetics. We now know that they are bacteria, but with many original features. Their genome is linear with a unique mode of replication, not circular like those of nearly all other bacteria.

Imaging mass spectrometry reveals highly specific interactions between actinomycetes to activate specialized metabolic gene clusters.

The genomes of actinomycetes contain numerous gene clusters potentially able to encode the production of many antibiotics and other specialized metabolites that are not expressed during growth under typical laboratory conditions. Undoubtedly, this reflects the soil habitat of these organisms, which is highly complex physically, chemically, and biotically; the majority of the compounds that make up the specialized metabolome are therefore adaptive only under specific conditions. While there have been numerous previous reports of "waking up" the "sleeping" gene clusters, many involving genetic interventions or nutritional challenges, the role of competing microorganisms has been comparatively little studied.

Feast or famine: the global regulator DasR links nutrient stress to antibiotic production by Streptomyces.

Members of the soil-dwelling prokaryotic genus Streptomyces produce many secondary metabolites, including antibiotics and anti-tumour agents. Their formation is coupled with the onset of development, which is triggered by the nutrient status of the habitat. We propose the first complete signalling cascade from nutrient sensing to development and antibiotic biosynthesis.

Generation of useful insertionally blocked sterol degradation pathway mutants of fast-growing mycobacteria and cloning, characterization, and expression of the terminal oxygenase of the 3-ketosteroid 9alpha-hydroxylase in Mycobacterium smegmatis mc(2)155.

Integration of the pCG79 temperature-sensitive plasmid carrying Tn611 was used to generate libraries of mutants with blocked sterol-transforming ability of the sterol-utilizing strains Mycobacterium smegmatis mc(2)155 and Mycobacterium phlei M51-Ept. Of the 10,000 insertional mutants screened from each library, 4 strains with altered activity of the sterol-degrading enzymes were identified. A blocked 4-androstene-3,17-dione-producing M.

The sugar phosphotransferase system of Streptomyces coelicolor is regulated by the GntR-family regulator DasR and links N-acetylglucosamine metabolism to the control of development.

Members of the soil-dwelling, sporulating prokaryotic genus Streptomyces are indispensable for the recycling of the most abundant polysaccharides on earth (cellulose and chitin), and produce a wide range of antibiotics and industrial enzymes. How do these organisms sense the nutritional state of the environment, and what controls the signal for the switch to antibiotic production and morphological development? Here we show that high extracellular concentrations of N-acetylglucosamine, the monomer of chitin, prevent Streptomyces coelicolor progressing beyond the vegetative state, and that this effect is absent in a mutant defective of N-acetylglucosamine transport. We provide evidence that the signal is transmitted through the GntR-family regulator DasR, which controls the N-acetylglucosamine regulon, including the pts genes ptsH, ptsI and crr needed for uptake of N-acetylglucosamine.

Soil to genomics: the Streptomyces chromosome.

The 8-9-Mb Streptomyces chromosome is linear, with a "core" containing essential genes and "arms" carrying conditionally adaptive genes that can sustain large deletions in the laboratory. Bidirectional chromosome replication from a central oriC is completed by "end-patching," primed from terminal proteins covalently bound to the free 5'-ends. Plasmid-mediated conjugation involves movement of double-stranded DNA by proteins resembling other bacterial motor proteins, probably via hyphal tip fusion, mediated by these transfer proteins.

Combinatorial polyketide biosynthesis by de novo design and rearrangement of modular polyketide synthase genes.

Type I polyketide synthase (PKS) genes consist of modules approximately 3-6 kb long, which encode the structures of 2-carbon units in polyketide products. Alteration or replacement of individual PKS modules can lead to the biosynthesis of 'unnatural' natural products but existing techniques for this are time consuming. Here we describe a generic approach to the design of synthetic PKS genes where facile cassette assembly and interchange of modules and domains are facilitated by a repeated set of flanking restriction sites.

Gas vesicles in actinomycetes: old buoys in novel habitats?

Gas vesicles are gas-filled prokaryotic organelles that function as flotation devices. This enables planktonic cyanobacteria and halophilic archaea to position themselves within the water column to make optimal use of light and nutrients. Few terrestrial microbes are known to contain gas vesicles.

Genome plasticity in Streptomyces: identification of 1 Mb TIRs in the S. coelicolor A3(2) chromosome.

The chromosomes of several widely used laboratory derivatives of Streptomyces coelicolor A3(2) were found to have 1.06 Mb inverted repeat sequences at their termini (i.e.

Cracking the polyketide code.

Polyketides, natural products from microorganisms, have been a main source of antibiotics. Understanding the 'programming' of the enzymes that produce these complex molecules has opened a new field of drug discovery

Synergy and contingency as driving forces for the evolution of multiple secondary metabolite production by Streptomyces species.

In this article we briefly review theories about the ecological roles of microbial secondary metabolites and discuss the prevalence of multiple secondary metabolite production by strains of Streptomyces, highlighting results from analysis of the recently sequenced Streptomyces coelicolor and Streptomyces avermitilis genomes. We address this question: Why is multiple secondary metabolite production in Streptomyces species so commonplace? We argue that synergy or contingency in the action of individual metabolites against biological competitors may, in some cases, be a powerful driving force for the evolution of multiple secondary metabolite production. This argument is illustrated with examples of the coproduction of synergistically acting antibiotics and contingently acting siderophores: two well-known classes of secondary metabolite.

Enhanced heterologous polyketide production in Streptomyces by exploiting plasmid co-integration.

A plasmid named pSMALL was discovered in a Streptomyces coelicolor strain that significantly enhanced the levels of production of 15-methyl-6-deoxyerythronolide B, a polyketide lactone normally produced in low amounts by engineered polyketide synthase (PKS) genes. It is a co-integrate between a conventional SCP2*-derived Streptomyces expression plasmid, pJRJ2, and SCP2@, a variant of the parental SCP2* plasmid. SCP2@ has a 45-bp deletion 35 bp upstream of the start codon of the repI gene in the replication region; and this correlated with an enhanced plasmid copy number and polyketide overproduction by its derivatives.