A gene cloning system for 'Streptomyces toyocaensis'

Resurrecting ancestral antibiotics: unveiling the origins of modern lipid II targeting glycopeptides

Antibiotics are central to modern medicine, and yet they are mainly the products of intra and inter-kingdom evolutionary warfare. To understand how nature evolves antibiotics around a common mechanism of action, we investigated the origins of an extremely valuable class of compounds, lipid II targeting glycopeptide antibiotics (GPAs, exemplified by teicoplanin and vancomycin), which are used as last resort for the treatment of antibiotic resistant bacterial infections. Using a molecule-centred approach and computational techniques, we first predicted the nonribosomal peptide synthetase assembly line of paleomycin, the ancestral parent of lipid II targeting GPAs. Subsequently, we employed synthetic biology techniques to produce the predicted peptide and validated its antibiotic activity. We revealed the structure of paleomycin, which enabled us to address how nature morphs a peptide antibiotic scaffold through evolution. In doing so, we obtained temporal snapshots of key selection domains in nonribosomal peptide synthesis during the biosynthetic journey from ancestral, teicoplanin-like GPAs to modern GPAs such as vancomycin. Our study demonstrates the synergy of computational techniques and synthetic biology approaches enabling us to journey back in time, trace the temporal evolution of antibiotics, and revive these ancestral molecules. It also reveals the optimisation strategies nature has applied to evolve modern GPAs, laying the foundation for future efforts to engineer this important class of antimicrobial agents.

Heterologous production of small molecules in the optimized Streptomyces hosts

Time span of literature covered: 2010-2018The genome mining of streptomycetes has revealed their great biosynthetic potential to produce novel natural products. One of the most promising exploitation routes of this biosynthetic potential is the refactoring and heterologous expression of corresponding biosynthetic gene clusters in a panel of specifically selected and optimized chassis strains. This article will review selected recent reports on heterologous production of natural products in streptomycetes. In the first part, the importance of heterologous production for drug discovery will be discussed. In the second part, the review will discuss recently developed genetic control elements (such as promoters, ribosome binding sites, terminators) and their application to achieve successful heterologous expression of biosynthetic gene clusters. Finally, the most widely used Streptomyces hosts for heterologous expression of biosynthetic gene clusters will be compared in detail. The article will be of interest to natural product chemists, molecular biologists, pharmacists and all individuals working in the natural products drug discovery field.

Kistamicin biosynthesis reveals the biosynthetic requirements for production of highly crosslinked glycopeptide antibiotics

Kistamicin is a divergent member of the glycopeptide antibiotics, a structurally complex class of important, clinically relevant antibiotics often used as the last resort against resistant bacteria. The extensively crosslinked structure of these antibiotics that is essential for their activity makes their chemical synthesis highly challenging and limits their production to bacterial fermentation. Kistamicin contains three crosslinks, including an unusual 15-membered A-O-B ring, despite the presence of only two Cytochrome P450 Oxy enzymes thought to catalyse formation of such crosslinks within the biosynthetic gene cluster. In this study, we characterise the kistamicin cyclisation pathway, showing that the two Oxy enzymes are responsible for these crosslinks within kistamicin and that they function through interactions with the X-domain, unique to glycopeptide antibiotic biosynthesis. We also show that the kistamicin OxyC enzyme is a promiscuous biocatalyst, able to install multiple crosslinks into peptides containing phenolic amino acids.

Kistamicin is a structurally divergent glycopeptide antibiotic (GPA) that contains a unique 15-membered A-O-B ring. Here, the authors obtained a crystal structure of the kistamicin OxyA/X-domain complex and analysed the cyclisation cascade leading to the formation of the A-O-B ring.

The ΦBT1 large serine recombinase catalyzes DNA integration at pseudo-attB sites in the genus Nocardia

Plasmid vectors based on bacteriophage integrases are important tools in molecular microbiology for the introduction of foreign DNA, especially into bacterial species where other systems for genetic manipulation are limited. Site specific integrases catalyze recombination between phage and bacterial attachment sites (attP and attB, respectively) and the best studied integrases in the actinomycetes are the serine integrases from the Streptomyces bacteriophages ΦC31 and ΦBT1. As this reaction is unidirectional and highly stable, vectors containing phage integrase systems have been used in a number of genetic engineering applications. Plasmids bearing the ΦBT1 integrase have been used to introduce DNA into Streptomyces and Amycolatopsis strains; however, they have not been widely studied in other actinobacterial genera. Here, we show that vectors based on ΦBT1 integrase can stably integrate into the chromosomes of a range of Nocardia species, and that this integration occurs despite the absence of canonical attB sites in these genomes. Furthermore, we show that a ΦBT1 integrase-based vector can insert at multiple pseudo-attB sites within a single strain and we determine the sequence of a pseudo-attB motif. These data suggest that ΦBT1 integrase-based vectors can be used to readily and semi-randomly introduce foreign DNA into the genomes of a range of Nocardia species. However, the precise site of insertion will likely require empirical determination in each species to avoid unexpected off-target effects.

Old and new glycopeptide antibiotics: From product to gene and back in the post-genomic era

Glycopeptide antibiotics are drugs of last resort for treating severe infections caused by multi-drug resistant Gram-positive pathogens. First-generation glycopeptides (vancomycin and teicoplanin) are produced by soil-dwelling actinomycetes. Second-generation glycopeptides (dalbavancin, oritavancin, and telavancin) are semi-synthetic derivatives of the progenitor natural products. Herein, we cover past and present biotechnological approaches for searching for and producing old and new glycopeptide antibiotics. We review the strategies adopted to increase microbial production (from classical strain improvement to rational genetic engineering), and the recent progress in genome mining, chemoenzymatic derivatization, and combinatorial biosynthesis for expanding glycopeptide chemical diversity and tackling the never-ceasing evolution of antibiotic resistance.

An Efficient Method To Generate Gene Deletion Mutants of the Rapamycin-Producing Bacterium Streptomyces iranensis HM 35

Streptomyces iranensis HM 35 is an alternative rapamycin producer to Streptomyces rapamycinicus Targeted genetic modification of rapamycin-producing actinomycetes is a powerful tool for the directed production of rapamycin derivatives, and it has also revealed some key features of the molecular biology of rapamycin formation in S. rapamycinicus. The approach depends upon efficient conjugational plasmid transfer from Escherichia coli to Streptomyces, and the failure of this step has frustrated its application to Streptomyces iranensis HM 35. Here, by systematically optimizing the process of conjugational plasmid transfer, including screening of various media, and by defining optimal temperatures and concentrations of antibiotics and Ca(2+) ions in the conjugation media, we have achieved exconjugant formation for each of a series of gene deletions in S. iranensis HM 35. Among them were rapK, which generates the starter unit for rapamycin biosynthesis, and hutF, encoding a histidine catabolizing enzyme. The protocol that we have developed may allow efficient generation of targeted gene knockout mutants of Streptomyces species that are genetically difficult to manipulate.

IMPORTANCE

The developed protocol of conjugational plasmid transfer from Escherichia coli to Streptomyces iranensis may allow efficient generation of targeted gene knockout mutants of other genetically difficult to manipulate, but valuable, Streptomyces species.

Genetic manipulation of secondary metabolite biosynthesis for improved production in Streptomyces and other actinomycetes

Actinomycetes continue to be important sources for the discovery of secondary metabolites for applications in human medicine, animal health, and crop protection. With the maturation of actinomycete genome mining as a robust approach to identify new and novel cryptic secondary metabolite gene clusters, it is critical to continue developing methods to activate and enhance secondary metabolite biosynthesis for discovery, development, and large-scale manufacturing. This review covers recent reports on promising new approaches and further validations or technical improvements of existing approaches to strain improvement applicable to a wide range of Streptomyces species and other actinomycetes.

Artificial chromosomes to explore and to exploit biosynthetic capabilities of actinomycetes

Actinomycetes are an important source of biologically active compounds, like antibiotics, antitumor agents, and immunosuppressors. Genome sequencing is revealing that this class of microorganisms has larger genomes relative to other bacteria and uses a considerable fraction of its coding capacity (5–10%) for the production of mostly cryptic secondary metabolites. To access actinomycetes biosynthetic capabilities or to improve the pharmacokinetic properties and production yields of these chemically complex compounds, genetic manipulation of the producer strains can be performed. Heterologous expression in amenable hosts can be useful to exploit and to explore the genetic potential of actinomycetes and not cultivable but interesting bacteria. Artificial chromosomes that can be stably integrated into the Streptomyces genome were constructed and demonstrated to be effective for transferring entire biosynthetic gene clusters from intractable actinomycetes into more suitable hosts. In this paper, the construction of several shuttle Escherichia coli-Streptomyces artificial chromosomes is discussed together with old and new strategies applied to improve heterologous production of secondary metabolites.

Streptomyces temperate bacteriophage integration systems for stable genetic engineering of actinomycetes (and other organisms)

ϕC31, ϕBT1, R4, and TG1 are temperate bacteriophages with broad host specificity for species of the genus Streptomyces. They form lysogens by integrating site-specifically into diverse attB sites located within individual structural genes that map to the conserved core region of streptomycete linear chromosomes. The target genes containing the ϕC31, ϕBT1, R4, and TG1 attB sites encode a pirin-like protein, an integral membrane protein, an acyl-CoA synthetase, and an aminotransferase, respectively. These genes are highly conserved within the genus Streptomyces, and somewhat conserved within other actinomycetes. In each case, integration is mediated by a large serine recombinase that catalyzes unidirectional recombination between the bacteriophage attP and chromosomal attB sites. The unidirectional nature of the integration mechanism has been exploited in genetic engineering to produce stable recombinants of streptomycetes, other actinomycetes, eucaryotes, and archaea. The ϕC31 attachment/integration (Att/Int) system has been the most widely used, and it has been coupled with the ϕBT1 Att/Int system to facilitate combinatorial biosynthesis of novel lipopeptide antibiotics in Streptomyces fradiae.

Tailoring enzyme-rich environmental DNA clones: a source of enzymes for generating libraries of unnatural natural products

A detailed bioinformatics analysis of six glycopeptide biosynthetic gene clusters isolated from soil environmental DNA (eDNA) megalibraries indicates that a subset of these gene clusters contains collections of tailoring enzymes that are predicted to result in the production of new glycopeptide congeners. In particular, sulfotransferases appear in eDNA-derived gene clusters at a much higher frequency than would be predicted from the characterization of glycopeptides from cultured Actinomycetes . Enzymes found on tailoring-enzyme-rich eDNA clones associated with these six gene clusters were used to produce a series of new sulfated glycopeptide derivatives in both in vitro and in vivo derivatization studies. The derivatization of known natural products with eDNA-derived tailoring enzymes is likely to be a broadly applicable strategy for generating libraries of new natural product variants.

Chapter 18. Molecular genetic approaches to analyze glycopeptide biosynthesis

The glycopeptide antibiotics vancomycin and teicoplanin are used in the hospital as drugs of last resort to combat resistant Gram-positive pathogens, in particular methicillin-resistant Staphylococcus aureus. All glycopeptides consist of a heptapeptide backbone in which the aromatic residues are connected to form a rigid cup-shaped structure required to stably interact with the D-Ala-D-Ala terminus of bacterial cell wall precursors. Structural diversity is generated by variations in the composition of the backbone, preferably at amino acid positions 1 and 3, and by different glycosylation, methylation, and chlorination patterns. The identification of several glycopeptide biosynthesis gene clusters, the development of genetic techniques to manipulate at least some of the producing actinomycetes, and subsequent molecular analysis enabled the elucidation of their biosynthetic pathways. This led to biochemical methods being combined with molecular genetic techniques and analytical chemistry. Knowledge of the biosynthesis made it possible to apply different approaches for the generation of novel glycopeptide derivatives by mutasynthesis, precursor-directed biosynthesis, and genetic engineering.

Integrative gene cloning and expression system for Streptomyces sp. US 24 and Streptomyces sp. TN 58 bioactive molecule producing strains

Streptomyces sp. US 24 and Streptomyces sp. TN 58, two strains producing interesting bioactive molecules, were successfully transformed using E. coli ET12567 (pUZ8002), as a conjugal donor, carrying the integrative plasmid pSET152. For the Streptomyces sp. US 24 strain, two copies of this plasmid were tandemly integrated in the chromosome, whereas for Streptomyces sp. TN 58, the integration was in single copy at the attB site. Plasmid pSET152 was inherited every time for all analysed Streptomyces sp. US 24 and Streptomyces sp. TN 58 exconjugants under nonselective conditions. The growth, morphological differentiation, and active molecules production of all studied pSET152 integrated exconjugants were identical to those of wild type strains. Consequently, conjugal transfer using pSET152 integration system is a suitable means of genes transfer and expression for both studied strains. To validate the above gene transfer system, the glucose isomerase gene (xylA) from Streptomyces sp. SK was expressed in strain Streptomyces sp. TN 58. Obtained results indicated that heterologous glucose isomerase could be expressed and folded effectively. Glucose isomerase activity of the constructed TN 58 recombinant strain is of about eighteenfold higher than that of the Streptomyces sp. SK strain. Such results are certainly of importance due to the potential use of improved strains in biotechnological process for the production of high-fructose syrup from starch.

The Biosynthesis of Teicoplanin-Type Glycopeptide Antibiotics: Assignment of P450 Mono-Oxygenases to Side Chain Cyclizations of Glycopeptide A47934

Streptomyces toyocaensis produces A47934, a teicoplanin-like type-IV glycopeptide with antibiotic activity against methicillin-resistant Staphylococcus aureus. A47934 differs from the type-I vancomycin glycopeptides, which possess a tricyclic peptide backbone, by the presence of an additional ring closure between the aromatic amino acids 1 and 3. To elucidate the order of crosslinking reactions, P450 mono-oxygenase-inactivation mutants (DeltastaF, DeltastaG, DeltastaH, and DeltastaJ) of the A47934 producer were generated, and the accumulated intermediates were analyzed. Thus, the formation of each crosslink could unambiguously be assigned to a specific oxygenase. The structure of the released intermediates from the wild-type nonribosomal peptide synthetase assembly line facilitated the determination of the cyclization order. Unexpectedly, the additional ring closure in A47934, catalyzed by StaG, is the second oxygenase reaction.

Intergeneric conjugation in holomycin-producing marine Streptomyces sp. strain M095

Marine Streptomyces are potential candidates for novel natural products and industrial catalysts. In order to set up biosynthesis approach for a holomycin-producing strain M095 isolated from Jiaozhou Bay, China, a genetic transformation system was established using intergeneric conjugation. The plasmid pIJ8600 consists of an origin of replication for Escherichia coli, a phage integrase directing efficient site-specific integration in bacterial chromosome, thiostrepton-induced promoter and an attP sequence. Using E. coli ET12567 (pUZ8002) carrying pIJ8600 as a conjugal donor, while it was mated with strain M095, pIJ8600 was mobilized to the recipient and the transferred DNA was also integrated into the recipient chromosome. The frequency of exconjugants was 1.9+/-0.13x10(-4) per recipient cell. Analysis of eight exconjugants showed pIJ8600 was stable integrated at a single chromosomal site (attB) of the Streptomyces genome. The DNA sequence of the attB was cloned and shown to be conserved. The results of growth and antimicrobial activity analysis indicated that the integration of pIJ8600 did not seem to affect the biosynthesis of antibiotics or other essential amino acids. To demonstrate the feasibility of above gene transfer system, the allophycocyanin gene (apc) from cyanobacterium Anacystis nidulans UTEX625 was expressed in strain M095, and the results indicated heterologous allophycocyanin could be expressed and folded effectively.

Biosynthesis of sulfated glycopeptide antibiotics by using the sulfotransferase StaL

The unique glycopeptide antibiotic A47934, produced by Streptomyces toyocaensis, possesses a nonglycosylated heptapeptide core that is sulfated on the phenolic hydroxyl of the N-terminal 4-hydroxy-L-phenylglycine residue. Genetic and biochemical experiments confirmed that StaL is a sulfotransferase capable of sulfating the predicted crosslinked heptapeptide substrate to produce A47934 both in vivo and in vitro. Incubation of purified His(6)-StaL with various substrates in vitro revealed substrate specificity and yielded two sulfo-glycopeptide antibiotics: sulfo-teicoplanin aglycone and sulfo-teicoplanin. Quantification of the antibacterial activity of desulfo-A47934, A47934, teicoplanin, and sulfo-teicoplanin demonstrated that sulfation slightly increased the minimum inhibitory concentration. This unique modification by sulfation expands glycopeptide diversity with potential application for the development of new antibiotics.

Understanding and manipulating glycopeptide pathways: the example of the dalbavancin precursor A40926

Glycopeptide antibiotics represent an important class of microbial compounds produced by several genera of actinomycetes. The emergence of resistance to glycopeptides among enterococci and staphylococci has prompted the search for second-generation drugs of this class and semi-synthetic derivatives are currently under clinical trials. Dalbavancin is obtained by chemical modification of the natural glycopeptide A40926, produced by a Nonomuraea sp. Recently, there has been considerable progress in the elucidation of biosynthesis of glycopeptide antibiotics; several gene clusters have been characterized, thus providing an understanding of the biosynthesis of these chemically complex molecules. Furthermore, such investigations have yielded the first glycopeptide derivatives produced by genetic or enzymatic intervention. We have isolated and characterized the dbv clusters, involved in the formation of the glycopeptides A40926. The development of a gene-transfer system for Nonomuraea sp. has allowed the manipulation of the A40926 pathway. New derivatives were obtained by inactivating selected dbv genes. In addition, our data suggest differences in the biosynthetic routes for heptapeptide formation between the vancomycin and the teicoplanin families of glycopeptides.

Introduction of DNA into Actinomycetes by bacterial conjugation from E. coli—An evaluation of various transfer systems

Gene transfer is a basic requirement for optimizing bioactive natural substances produced by an increasing number of industrially used microorganisms. We have analyzed quantitatively horizontal gene transfer from Escherichia coli to Actinomycetes. The efficiencies of DNA transfer of four different systems were compared that consist of conjugative and mobilizable plasmids with a broad-host range. Three novel binary vector set-ups were constructed based on: (i) the IncQ group of mobilizable plasmids (RSF1010), (ii) IncQ-like pTF-FC2 and (iii) pSB102 that belongs to a new class of broad-host-range plasmids. The established system based on the IncPalpha group of conjugative plasmids served as the reference. For all plasmids constructed, we confirmed the functional integrity of the selected transfer machineries by intrageneric matings between E. coli strains. We demonstrate that the transfer systems introduced in this study are efficient in mediating gene transfer from E. coli to Actinomycetes and are possible alternatives for gene transfer into Actinomycetes for which the IncPalpha-based transfer system is not applicable. The use of plasmids that integrate into the recipients' chromosomes compared to that of plasmids replicating autonomously is shown to allow the access to a wider range of hosts.

Intergeneric conjugation in Streptomyces peucetius and Streptomyces sp. strain C5: chromosomal integration and expression of recombinant plasmids carrying the chiC gene

Intergeneric conjugal transfer of plasmid DNA from Escherichia coli to Streptomyces circumvents problems such as host-controlled restriction and instability of foreign DNA during the transformation of Streptomyces protoplasts. The anthracycline antibiotic-producing strains Streptomyces peucetius and Streptomyces sp. strain C5 were transformed using E. coli ET12567(pUZ8002) as a conjugal donor. When this donor species, carrying pSET152, was mated with Streptomyces strains, the resident plasmid was mobilized to the recipient and the transferred DNA was also integrated into the recipient chromosome. Analysis of the exconjugants showed stable integration of the plasmid at a single chromosomal site (attB) of the Streptomyces genome. The DNA sequence of the chromosomal integration site was determined and shown to be conserved. However, the core sequence, where the crossover presumably occurred in C5 and S. peucetius, is TTC. These results also showed that the phiC31 integrative recombination is active and the phage attP site is functional in S. peucetius as well as in C5. The efficiency and specificity of phiC31-mediated site-specific integration of the plasmid in the presence of a 3.7-kb homologous DNA sequence indicates that integrative recombination is preferred under these conditions. The integration of plasmid DNA did not affect antibiotic biosynthesis or biosynthesis of essential amino acids. Integration of a single copy of a mutant chiC into the wild-type S. peucetius chromosome led to the production of 30-fold more chitinase.

Assembling the glycopeptide antibiotic scaffold: The biosynthesis of A47934 from Streptomyces toyocaensis NRRL15009

The glycopeptide antibiotics vancomycin and teicoplanin are vital components of modern anti-infective chemotherapy exhibiting outstanding activity against Gram-positive pathogens including members of the genera Streptococcus, Staphylococcus, and Enterococcus. These antibiotics also provide fascinating examples of the chemical and associated biosynthetic complexity exploitable in the synthesis of natural products by actinomycetes group of bacteria. We report the sequencing and annotation of the biosynthetic gene cluster for the glycopeptide antibiotic from Streptomyces toyocaensis NRRL15009, the first complete sequence for a teicoplanin class glycopeptide. The cluster includes 34 ORFs encompassing 68 kb and includes all of the genes predicted to be required to synthesize and regulate its biosynthesis. The gene cluster also contains ORFs encoding enzymes responsible for glycopeptide resistance. This role was confirmed by insertional inactivation of the d-Ala-d-lactate ligase, vanAst, which resulted in the predicted -sensitive phenotype and impaired antibiotic biosynthesis. These results provide increased understanding of the biosynthesis of these complex natural products.

StoPK-1, a serine/threonine protein kinase from the glycopeptide antibiotic producer Streptomyces toyocaensis NRRL 15009, affects oxidative stress response

The glycopeptide antibiotic-producing bacterium, Streptomyces toyocaensis NRRL 15009, has proteins phosphorylated on Ser, Thr, Tyr and His, implying the presence of a battery of associated kinases. We have identified the Ser/Thr protein kinase gene fragments stoPK-1, stoPK-2, stoPK-3 and stoPK-4 from S. toyocaensis NRRL 15009 by a polymerase chain reaction (PCR) strategy using oligonucleotide primers based on eukaryotic Ser/Thr and Tyr kinase sequences. One of these (stoPK-1) was subsequently cloned in its entirety from a 3.2 kb genomic BamHI fragment. stoPK-1 encodes a 642-amino-acid protein with a predicted N-terminal Ser/Thr kinase domain and a C-terminal coiled-coil region divided by a membrane-spanning region. Expression of StoPK-1 in Escherichia coli yielded a protein confined to the membrane fraction, which was found to be phosphorylated exclusively on Thr residues and could transfer phosphate to the model substrates myelin basic protein and histone H1. Both autophosphorylation and phosphoryl transfer could be inhibited by the flavanoid apigenin. Disruption of stoPK-1 with the apramycin resistance gene in the S. toyo-caensis chromosome resulted in changes in mycelial morphology and an increased sensitivity to the redox cycling agents paraquat and nitrofurantoin on glucose-containing media. Supplying stoPK-1 or the S. coelicolor homologue pkaF in trans could reverse this sensitivity, whereas a catalytically inactive mutant of stoPK-1 could not, indicating that kinase activity is essential for this phenotype. This suggests a link between this membrane-bound protein kinase in signalling pathways sensitive to oxidative stress and/or glucose metabolism. These results broaden the roles of Ser/Thr protein kinases in bacteria and underscore the diversity of signal transduction mechanisms available to respond to various stimuli.

Genes for production of the enediyne antitumor antibiotic C-1027 in Streptomyces globisporus are clustered with the cagA gene that encodes the C-1027 apoprotein

C-1027, the most potent member of the enediyne antitumor antibiotic family, is produced by Streptomyces globisporus C-1027 and consists of an apoprotein (encoded by the cagA gene) and a nonpeptidic chromophore. The C-1027 chromophore could be viewed as being derived biosynthetically from a benzoxazolinate, a deoxyamino hexose, a beta-amino acid, and an enediyne core. By adopting a strategy for cloning of the C-1027 biosynthesis gene cluster by mapping a putative dNDP-glucose 4,6-dehydratase (NGDH) gene to cagA, we have localized 75 kb of contiguous DNA from S. globisporus. DNA sequence analysis of two regions of the cloned gene cluster revealed two genes, sgcA and sgcB, that encode an NGDH enzyme and a transmembrane efflux protein, respectively, and confirmed that the cagA gene resides approximately 14 kb upstream of the sgcAB locus. The involvement of the cloned gene cluster in C-1027 biosynthesis was demonstrated by disrupting the sgcA gene to generate C-1027-nonproducing mutants and by complementing the sgcA mutants in vivo to restore C-1027 production. These results represent the first cloning of a gene cluster for enediyne antitumor antibiotic biosynthesis and provide a starting point for future genetic and biochemical investigations of C-1027 biosynthesis.

Identification and analysis of the balhimycin biosynthetic gene cluster and its use for manipulating glycopeptide biosynthesis in Amycolatopsis mediterranei DSM5908

Seven complete genes and one incomplete gene for the biosynthesis of the glycopeptide antibiotic balhimycin were isolated from the producer, Amycolatopsis mediterranei DSM5908, by a reverse-cloning approach and characterized. Using oligonucleotides derived from glycosyltransferase sequences, a 900-bp glycosyltransferase gene fragment was amplified and used to identify a DNA fragment of 9,882 bp. Of the identified open reading frames, three (oxyA to -C) showed significant sequence similarities to cytochrome P450 monooxygenases and one (bhaA) showed similarities to halogenase, and the genes bgtfA to -C showed similarities to glycosyltransferases. Glycopeptide biosynthetic mutants were created by gene inactivation experiments eliminating oxygenase and glycosyltransferase functions. Inactivation of the oxygenase gene(s) resulted in a balhimycin mutant (SP1-1) which was not able to synthesize an antibiotically active compound. Structural analysis by high-performance liquid chromatography-mass spectrometry, fragmentation studies, and amino acid analysis demonstrated that these oxygenases are involved in the coupling of the aromatic side chains of the unusual heptapeptide. Mutant strain HD1, created by inactivation of the glycosyltransferase gene bgtfB, produced at least four different compounds which were not glycosylated but still antibiotically active.

High efficiency intergeneric conjugal transfer of plasmid DNA from Escherichia coli to methyl DNA-restricting streptomycetes

Many streptomycetes, including S. coelicolor A3(2), possess a potent methyl-specific restriction which can present an effective barrier to the introduction of heterologous DNA. We have compared the efficiency of intergeneric conjugal transfer of different types of plasmids to S. coelicolor and S. lividans 66 using two E. coli donors: the standard, methylation proficient strain S17-1, and the methylation deficient donor, ET12567(pUB307). We demonstrate that the methylation deficient donor can yield > 10(4)-fold more S. coelicolor exconjugants than the standard donor. In the case of pSET152 derivatives, which integrate into the host chromosome by site-specific recombination, up to 10% of streptomycete spores in the conjugation mixture inherit the plasmid. The conjugation procedure is efficient enough to obtain exconjugants with 'suicide' delivery plasmids and therefore provides a simple route for conducting gene disruptions in methyl DNA-restricting streptomycetes, and possibly other bacteria.

Production of hybrid glycopeptide antibiotics in vitro and in Streptomyces toyocaensis

BACKGROUND

The glycopeptide antibiotics vancomycin and teicoplanin are currently the last line of defence against some microorganisms that are resistant to many drugs. The emergence of vancomycin-resistant and teicoplanin-resistant enterococci underscores the need for more potent antibiotics. The glycosylation patterns of glycopeptides and chemical modifications of the glycosyl moieties have been shown to greatly influence their antibiotic activity, and certain combinations have resulted in highly active new compounds. To explore further the production of more potent glycopeptide antibiotics, we assessed whether glycosyltransferases could be used to produce hybrid compounds that contain various combinations of sugars and peptide cores.

RESULTS

We cloned five glycosyltransferase genes from Amycolatopsis orientalis strains that produce vancomycin or a related glycopeptide, A82846. The gtfB and gtfE' genes from A. orientalis strains expressed in Escherichia coli produced glucosyltransferase activities that added glucose or xylose to the vancomycin heptapeptide. The GtfE' protein added glucose efficiently to two other heptapeptides related to teicoplanin to produce hybrid glycopeptide antibiotics. The cloned gtfE' gene, driven by the strong constitutive promoter ermEp*, was introduced into Streptomyces toyocaensis, which produces the antibiotic A47934, a heptapeptide related to teicoplanin; recombinant organisms produced glucosyl A47934, a hybrid glycopeptide antibiotic.

CONCLUSIONS

Cloned glycosyltransferases from glycopeptide antibiotic producers can be used to produce novel hybrid antibiotics, both in vitro and in vivo. Because similar enzymes have differing degrees of substrate specificity, it is advantageous to characterize the substrate specificity with enzymes expressed in E. coli prior to constructing recombinant actinomycetes for production.