Structures and biological activities of cycloheptamycins A and B

The heptadepsipeptide cycloheptamycin A was isolated from the terrestrial Streptomyces sp. Tü 6314. Its constitution was elucidated on the basis of NMR spectroscopic experiments and mass spectrometric analysis. Its stereostructure was investigated by peptide hydrolysis and derivatization and firmly established by X-ray structure analysis. In addition to the parent compound, a new cycloheptamycin analog, cycloheptamycin B, was discovered and structurally assigned using comparative MS/MS experiments and NMR. The biological profile of both compounds was investigated, revealing a selective inhibitory potential of cycloheptamycins against Propionibacterium acnes.

Genome Mining of Streptomyces sp. Tü 6176: Characterization of the Nataxazole Biosynthesis Pathway

Streptomyces sp. Tü 6176 produces the cytotoxic benzoxazole nataxazole. Bioinformatic analysis of the genome of this organism predicts the presence of 38 putative secondary-metabolite biosynthesis gene clusters, including those involved in the biosynthesis of AJI9561 and its derivative nataxazole, the antibiotic hygromycin B, and ionophores enterobactin and coelibactin. The nataxazole biosynthesis gene cluster was identified and characterized: it lacks the O-methyltransferase gene required to convert AJI9561 into nataxazole. This O-methyltransferase activity might act as a resistance mechanism, as AJI9561 shows antibiotic activity whereas nataxazole is inactive. Moreover, heterologous expression of the nataxazole biosynthesis gene cluster in S. lividans JT46 resulted in the production of AJI9561. Nataxazole biosynthesis requires the shikimate pathway to generate 3-hydroxyanthranilate and an iterative type I PKS to generate 6-methylsalicylate. Production of nataxazole was improved up to fourfold by disrupting one regulatory gene in the cluster. An additional benzoxazole, 5-hydroxynataxazole is produced by Streptomyces sp. Tü 6176. 5-Hydroxynataxazole derives from nataxazole by the activity of an as yet unidentified oxygenase; this implies cross-talk between the nataxazole biosynthesis pathway and an unknown pathway.

Two Streptomyces species producing antibiotic, antitumor, and anti-inflammatory compounds are widespread among intertidal macroalgae and deep-sea coral reef invertebrates from the central Cantabrian Sea

Streptomycetes are widely distributed in the marine environment, although only a few studies on their associations to algae and coral ecosystems have been reported. Using a culture-dependent approach, we have isolated antibiotic-active Streptomyces species associated to diverse intertidal marine macroalgae (Phyllum Heterokontophyta, Rhodophyta, and Chlorophyta), from the central Cantabrian Sea. Two strains, with diverse antibiotic and cytotoxic activities, were found to inhabit these coastal environments, being widespread and persistent over a 3-year observation time frame. Based on 16S rRNA sequence analysis, the strains were identified as Streptomyces cyaneofuscatus M-27 and Streptomyces carnosus M-40. Similar isolates to these two strains were also associated to corals and other invertebrates from deep-sea coral reef ecosystem (Phyllum Cnidaria, Echinodermata, Arthropoda, Sipuncula, and Anelida) living up to 4.700-m depth in the submarine Avilés Canyon, thus revealing their barotolerant feature. These two strains were also found to colonize terrestrial lichens and have been repeatedly isolated from precipitations from tropospheric clouds. Compounds with antibiotic and cytotoxic activities produced by these strains were identified by high-performance liquid chromatography (HPLC) and database comparison. Antitumor compounds with antibacterial activities and members of the anthracycline family (daunomycin, cosmomycin B, galtamycin B), antifungals (maltophilins), anti-inflamatory molecules also with antituberculosis properties (lobophorins) were identified in this work. Many other compounds produced by the studied strains still remain unidentified, suggesting that Streptomyces associated to algae and coral ecosystems might represent an underexplored promising source for pharmaceutical drug discovery.

Draft Genome Sequence of Marine Actinomycete Streptomyces sp. Strain NTK 937, Producer of the Benzoxazole Antibiotic Caboxamycin

Streptomyces sp. strain NTK 937 is the producer of the benzoxazole antibiotic caboxamycin, which has been shown to exert inhibitory activity against Gram-positive bacteria, cytotoxic activity against several human tumor cell lines, and inhibition of the enzyme phosphodiesterase. In this genome announcement, we present a draft genome sequence of Streptomyces sp. NTK 937 in which we identified at least 35 putative secondary metabolite biosynthetic gene clusters.

Dermacozines H-J isolated from a deep-sea strain of Dermacoccus abyssi from Mariana Trench sediments

Dermacoccus abyssi sp. nov. strains MT1.1 and MT1.2 are actinomycetes isolated from a Mariana Trench sediment at a depth of 10 898 m. The fermentation process using complex media led to the production of three new pigmented heteroaromatic (oxidized and reduced) phenazine compounds, dermacozines H-J (1-3). Extensive use was made of 1D and 2D NMR experiments and high-resolution MS to determine the structures of the compounds. The new dermacozines showed radical scavenging activity, and the highest activity was observed for dermacozine H (1), with an IC50 value of 18.8 μM.

Growth inhibition of an Araucaria angustifolia (Coniferopsida) fungal seed pathogen, Neofusicoccum parvum, by soil streptomycetes

BACKGROUND

Araucariaceae are important forest trees of the southern hemisphere. Life expectancy of their seedlings can largely be reduced by fungal infections. In this study we have isolated and characterized such a fungus and investigated the potential of Streptomyces Actinobacteria from the respective rhizosphere to act as antagonists.

RESULTS

The pathogenic fungus from Araucaria angustifolia seeds was identified by morphological markers (pore-associated Woronin-bodies) as belonging to the Pezizomycotina. Molecular data identified the fungus as Neofusicoccum parvum (Botryosphaeriaceae). Co-cultures on agar of this fungus with certain streptomycete isolates from the rhizosphere, and from the surface of Araucaria roots significantly reduced the growth of the fungus. HPLC analysis of the agar yielded streptomycete-specific exudate compounds which were partly identified. There were differences in compounds between single (bacteria, fungus) and dual cultures (bacteria + fungus).

CONCLUSION

Streptomycetes from the rhizosphere of Araucariaceae produce exudates which can suppress the development of pathogenic fungi in their seeds.

Warkmycin, a novel angucycline antibiotic produced by Streptomyces sp. Acta 2930*

A novel angucycline-type antibiotic, warkmycin, was isolated from the culture filtrate of Streptomyces strain Acta 2930. Its chemical structure was elucidated by HR-MS, one-dimensional and 2D NMR experiments. The compound inhibits the growth of Gram-positive bacteria and shows a strong antiproliferative activity against mouse fibroblast cell line NIH-3T3 and human cancer cell lines HepG2 and HT29.

Production of fungal and bacterial growth modulating secondary metabolites is widespread among mycorrhiza-associated streptomycetes

BACKGROUND

Studies on mycorrhiza associated bacteria suggest that bacterial-fungal interactions play important roles during mycorrhiza formation and affect plant health. We surveyed Streptomyces Actinobacteria, known as antibiotic producers and antagonists of fungi, from Norway spruce mycorrhizas with predominantly Piloderma species as the fungal partner.

RESULTS

Fifteen Streptomyces isolates exhibited substantial variation in inhibition of tested mycorrhizal and plant pathogenic fungi (Amanita muscaria, Fusarium oxysporum, Hebeloma cylindrosporum, Heterobasidion abietinum, Heterobasidion annosum, Laccaria bicolor, Piloderma croceum). The growth of the mycorrhiza-forming fungus Laccaria bicolor was stimulated by some of the streptomycetes, and Piloderma croceum was only moderately affected. Bacteria responded to the streptomycetes differently than the fungi. For instance the strain Streptomyces sp. AcM11, which inhibited most tested fungi, was less inhibitory to bacteria than other tested streptomycetes. The determined patterns of Streptomyces-microbe interactions were associated with distinct patterns of secondary metabolite production. Notably, potentially novel metabolites were produced by strains that were less antagonistic to fungi. Most of the identified metabolites were antibiotics (e.g. cycloheximide, actiphenol) and siderophores (e.g. ferulic acid, desferroxiamines). Plant disease resistance was activated by a single streptomycete strain only.

CONCLUSIONS

Mycorrhiza associated streptomycetes appear to have an important role in inhibiting the growth of fungi and bacteria. Additionally, our study indicates that the Streptomyces strains, which are not general antagonists of fungi, may produce still un-described metabolites.

Langkolide, a 32-membered macrolactone antibiotic produced by Streptomyces sp. Acta 3062

A new 32-membered macrolactone antibiotic, named langkolide, was isolated from the mycelium of Streptomyces sp. Acta 3062. The langkolide structure was determined by HR-MS and 1D and 2D NMR as a 32-membered macrolactone connected from an overhanging polyketide tail to a naphthoquinone unit mediated by two carbohydrate moieties. The producing strain was isolated from a rhizosphere soil of Clitorea sp. collected at Burau Bay, Langkawi, Malaysia, and was characterized by its morphological and chemotaxonomic features in addition to its 16S rRNA gene sequence. It was identified as a member of the Streptomyces galbus clade. Langkolide exhibited various bioactivities including antimicrobial and antiproliferative activities. Furthermore, langkolide inhibited human recombinant phosphodiesterase 4 with an IC(50) value of 0.48 μM.

Mutational analysis of a phenazine biosynthetic gene cluster in Streptomyces anulatus 9663

The biosynthetic gene cluster for endophenazines, i.e., prenylated phenazines from Streptomyces anulatus 9663, was heterologously expressed in several engineered host strains derived from Streptomyces coelicolor M145. The highest production levels were obtained in strain M512. Mutations in the rpoB and rpsL genes of the host, which result in increased production of other secondary metabolites, had no beneficial effect on the production of phenazines. The heterologous expression strains produced, besides the known phenazine compounds, a new prenylated phenazine, termed endophenazine E. The structure of endophenazine E was determined by high-resolution mass spectrometry and by one- and two-dimensional NMR spectroscopy. It represented a conjugate of endophenazine A (9-dimethylallylphenazine-1-carboxylic acid) and L-glutamine (L-Gln), with the carboxyl group of endophenazine A forming an amide bond to the α-amino group of L-Gln. Gene inactivation experiments in the gene cluster proved that ppzM codes for a phenazine N-methyltransferase. The gene ppzV apparently represents a new type of TetR-family regulator, specifically controlling the prenylation in endophenazine biosynthesis. The gene ppzY codes for a LysR-type regulator and most likely controls the biosynthesis of the phenazine core. A further putative transcriptional regulator is located in the vicinity of the cluster, but was found not to be required for phenazine or endophenazine formation. This is the first investigation of the regulatory genes of phenazine biosynthesis in Streptomyces.

Biosynthetic gene cluster of the non-ribosomally synthesized cyclodepsipeptide skyllamycin: deciphering unprecedented ways of unusual hydroxylation reactions

The cyclic depsipeptide skyllamycin A is a potent inhibitor of the platelet-derived growth factor (PDGF) signaling pathway by inhibiting binding of homodimeric PDGF BB to the PDGF β-receptor. Its structure contains a cinnamoyl side chain and shows a high amount of β-hydroxylated amino acids as well as an unusual α-hydroxyglycine moiety as a rare structural modification. The skyllamycin biosynthetic gene cluster was cloned and sequenced from Streptomyces sp. Acta 2897. Its analysis revealed the presence of open reading frames encoding proteins for fatty acid precursor biosynthesis, non-ribosomal peptide synthetases, regulators, and transporters along with other modifying enzymes. Specific in-frame mutagenesis of these tailoring enzymes resulted in the production of novel skyllamycin derivatives revealing that β-hydroxy groups in skyllamycin A are introduced by a promiscuous cytochrome P450 monooxygenase, whereas a two-component flavin-dependent monooxygenase is involved in α-hydroxylation.

The biosynthetic genes for prenylated phenazines are located at two different chromosomal loci of Streptomyces cinnamonensis DSM 1042

Streptomyces cinnamonensis DSM 1042 produces two types of isoprenoid secondary metabolites: the prenylated naphthalene derivative furanonaphthoquinone I (FNQ I), and isoprenylated phenazines which are termed endophenazines. Previously, a 55 kb gene cluster was identified which contained genes for both FNQ I and endophenazine biosynthesis. However, several genes required for the biosynthesis of these metabolites were not present in this cluster. We now re-screened the cosmid library for genes of the mevalonate pathway and identified a separate genomic locus which contains the previously missing genes. This locus (15 kb) comprised orthologues of four phenazine biosynthesis genes known from Pseudomonas strains. Furthermore, the locus contained a putative operon of six genes of the mevalonate pathway, as well as the gene epzP which showed sequence similarity to a recently discovered class of prenyltransferases. Inactivation and complementation experiments proved the involvement of epzP in the prenylation reaction in endophenazine biosynthesis. This newly identified genomic locus is more than 40 kb distant from the previously identified cluster. The protein EpzP was expressed in Escherichia coli in form of a his-tag fusion protein and purified. The enzyme catalysed the prenylation of 5,10-dihydrophenazine-1-carboxylic acid (dihydro-PCA) using dimethylallyl diphosphate (DMAPP) as isoprenoid substrate. K(m) values were determined as 108 µM for dihydro-PCA and 25 µM for DMAPP.

Structures of the TetR-like simocyclinone efflux pump repressor, SimR, and the mechanism of ligand-mediated derepression

Simocyclinone D8 (SD8), a potent DNA gyrase inhibitor made by Streptomyces antibioticus, is exported from the producing organism by the SimX efflux pump. The expression of simX is under the control of SimR, a member of the TetR family of transcriptional regulators. SimR represses simX transcription by binding to operators in the intergenic region between simR and simX. Previously, we have shown that the mature antibiotic SD8 or its biosynthetic intermediate, simocyclinone C4, can dissociate SimR from its operators, leading to derepression of simX and export of SD8 from the cell. This provides a mechanism that couples the biosynthesis of the antibiotic to its export. Here, we report the crystal structures of SimR alone and in complex with either SD8 or simocyclinone C4. The ligand-binding pocket is unusual compared to those of other characterized TetR-family transcriptional regulators: the structures show an extensive ligand-binding pocket spanning both monomers in the functional dimeric unit, with the aminocoumarin moiety of SD8 buried in the protein core, while the angucyclic polyketide moiety is partially exposed to bulk solvent. Through comparisons of the structures, we postulate a derepression mechanism for SimR that invokes rigid-body motions of the subunits relative to one another, coupled with a putative locking mechanism to restrict further conformational change.

A crystal structure of the bifunctional antibiotic simocyclinone D8, bound to DNA gyrase

Simocyclinones are bifunctional antibiotics that inhibit bacterial DNA gyrase by preventing DNA binding to the enzyme. We report the crystal structure of the complex formed between the N-terminal domain of the Escherichia coli gyrase A subunit and simocyclinone D8, revealing two binding pockets that separately accommodate the aminocoumarin and polyketide moieties of the antibiotic. These are close to, but distinct from, the quinolone-binding site, consistent with our observations that several mutations in this region confer resistance to both agents. Biochemical studies show that the individual moieties of simocyclinone D8 are comparatively weak inhibitors of gyrase relative to the parent compound, but their combination generates a more potent inhibitor. Our results should facilitate the design of drug molecules that target these unexploited binding pockets.

Multiple convergence in polyketide biosynthesis: a third folding mode to the anthraquinone chrysophanol

The polyketide chrysophanol is shown to be formed, in an organism-specific way, by a third folding mode, involving a remarkable cyclization of a bicyclic diketo precursor, thus establishing the first example of multiple convergence in polyketide biosynthesis.

Convergence in the biosynthesis of acetogenic natural products from plants, fungi, and bacteria

This review deals with polyketides to which nature has developed different biosynthetic pathways in the course of evolution. The anthraquinone chrysophanol is the first example of an acetogenic natural product that is, in an organism-specific manner, formed via more than one polyketide folding mode: In eukaryotes, like e.g., in fungi, in higher plants, and in insects, it is synthesized via folding mode F, while in prokaryotes it originates through mode S. It has, more recently, even been found to be synthesized by a third pathway, named mode S'. Thus, chrysophanol is the first polyketide synthase product that originates through a divergent-convergent biosynthesis (depending on the respective producing organisms). A second example of a striking biosynthetic convergence is the isoquinoline alkaloids. While all as yet investigated representatives of this large family of plant-derived metabolites (more than 2500 known representatives!) are formed from aromatic amino acids, the biosynthetic origin of naphthylisoquinoline alkaloids like dioncophylline A is unprecedented in following a route to isoquinolines in plants: we have shown that such naphthylisoquinolines represent the as yet only known polyketidic di- and tetrahydroisoquinolines, originating from acetate and malonate units, exclusively. Both molecular halves, the isoquinoline part and the naphthalene portion, are even synthesized from a joint polyketide precursor, the first proven case of the F-type folding mode in higher plants. The biosynthetic origins of the natural products presented in this paper were elucidated by feeding (13)C(2)-labeled acetate (or advanced precursors) to the respective producing organisms, with subsequent NMR analysis of their (13)C(2) incorporation patterns using the potent cryoprobe methodology, thus making the full polyketide folding pattern visible.

Lipocarbazoles, secondary metabolites from Tsukamurella pseudospumae Acta 1857 with antioxidative activity

A family of new secondary metabolites with a carbazole moiety and an alkyl side chain was isolated from Tsukamurella pseudospumae strain Acta 1857. They were named lipocarbazoles in accordance with their chemical structures, which were determined by mass spectrometry and NMR spectroscopy. Lipocarbazoles are free radical scavengers showing antioxidative activity.

Coupling of the biosynthesis and export of the DNA gyrase inhibitor simocyclinone in Streptomyces antibioticus

Because most antibiotics are potentially lethal to the producing organism, there must be mechanisms to ensure that the machinery responsible for export of the mature antibiotic is in place at the time of biosynthesis. Simocyclinone D8 is a potent DNA gyrase inhibitor produced by Streptomyces antibioticus Tü 6040. Within the simocyclinone biosynthetic cluster are two divergently transcribed genes, simR and simX, encoding proteins that resemble the TetR/TetA repressor-efflux pump pair that cause widespread resistance to clinically important tetracyclines. Engineered expression of simX from a strong, heterologous promoter conferred high level simocyclinone D8 resistance on Streptomyces lividans, showing that simX encodes a simocyclinone efflux pump. Transcription of simX is controlled by SimR, which directly represses the simX and simR promoters by binding to two operator sites in the simX-simR intergenic region. Simocyclinone D8 abolishes DNA binding by SimR, providing a mechanism that couples the biosynthesis of simocyclinone to its export. In addition, an intermediate in the biosynthetic pathway, simocyclinone C4, which is essentially inactive as a DNA gyrase inhibitor, also induces simX expression in vivo and relieves simX repression by SimR in vitro.

Aromatic prenylation in phenazine biosynthesis: dihydrophenazine-1-carboxylate dimethylallyltransferase from Streptomyces anulatus

The bacterium Streptomyces anulatus 9663, isolated from the intestine of different arthropods, produces prenylated derivatives of phenazine 1-carboxylic acid. From this organism, we have identified the prenyltransferase gene ppzP. ppzP resides in a gene cluster containing orthologs of all genes known to be involved in phenazine 1-carboxylic acid biosynthesis in Pseudomonas strains as well as genes for the six enzymes required to generate dimethylallyl diphosphate via the mevalonate pathway. This is the first complete gene cluster of a phenazine natural compound from streptomycetes. Heterologous expression of this cluster in Streptomyces coelicolor M512 resulted in the formation of prenylated derivatives of phenazine 1-carboxylic acid. After inactivation of ppzP, only nonprenylated phenazine 1-carboxylic acid was formed. Cloning, overexpression, and purification of PpzP resulted in a 37-kDa soluble protein, which was identified as a 5,10-dihydrophenazine 1-carboxylate dimethylallyltransferase, forming a C-C bond between C-1 of the isoprenoid substrate and C-9 of the aromatic substrate. In contrast to many other prenyltransferases, the reaction of PpzP is independent of the presence of magnesium or other divalent cations. The K(m) value for dimethylallyl diphosphate was determined as 116 microm. For dihydro-PCA, half-maximal velocity was observed at 35 microm. K(cat) was calculated as 0.435 s(-1). PpzP shows obvious sequence similarity to a recently discovered family of prenyltransferases with aromatic substrates, the ABBA prenyltransferases. The present finding extends the substrate range of this family, previously limited to phenolic compounds, to include also phenazine derivatives.

Albidopyrone, a new alpha-pyrone-containing metabolite from marine-derived Streptomyces sp. NTK 227

Albidopyrone, a new alpha-pyrone-containing secondary metabolite, was produced by Streptomyces sp. NTK 227, a strain isolated from Atlantic Ocean sediment and found to be a member of the Streptomyces albidoflavus 16S rRNA gene clade. The structure of the compound was determined by MS and NMR spectroscopy, and found to have a moderate inhibitory activity against protein-tyrosin phosphatase B.

Biosynthetic investigations of lactonamycin and lactonamycin z: cloning of the biosynthetic gene clusters and discovery of an unusual starter unit

The antibiotics lactonamycin and lactonamycin Z provide attractive leads for antibacterial drug development. Both antibiotics contain a novel aglycone core called lactonamycinone. To gain insight into lactonamycinone biosynthesis, cloning and precursor incorporation experiments were undertaken. The lactonamycin gene cluster was initially cloned from Streptomyces rishiriensis. Sequencing of ca. 61 kb of S. rishiriensis DNA revealed the presence of 57 open reading frames. These included genes coding for the biosynthesis of l-rhodinose, the sugar found in lactonamycin, and genes similar to those in the tetracenomycin biosynthetic gene cluster. Since lactonamycin production by S. rishiriensis could not be sustained, additional proof for the identity of the S. rishiriensis cluster was obtained by cloning the lactonamycin Z gene cluster from Streptomyces sanglieri. Partial sequencing of the S. sanglieri cluster revealed 15 genes that exhibited a very high degree of similarity to genes within the lactonamycin cluster, as well as an identical organization. Double-crossover disruption of one gene in the S. sanglieri cluster abolished lactonamycin Z production, and production was restored by complementation. These results confirm the identity of the genetic locus cloned from S. sanglieri and indicate that the highly similar locus in S. rishiriensis encodes lactonamycin biosynthetic genes. Precursor incorporation experiments with S. sanglieri revealed that lactonamycinone is biosynthesized in an unusual manner whereby glycine or a glycine derivative serves as a starter unit that is extended by nine acetate units. Analysis of the gene clusters and of the precursor incorporation data suggested a hypothetical scheme for lactonamycinone biosynthesis.

Spirodionic Acid, a Novel Metabolite fromStreptomyces sp., Part 1: Structure Elucidation and Diels–Alder-Type Biosynthesis

Spirodionic acid (1), a novel microbial metabolite with a spiro[4.5]decene skeleton, the 6-ethyl-2H-pyrone 5, dihydrosarkomycin (6), and other metabolites were isolated from the strain Streptomyces sp. Tü 6077. Structural elucidation was accomplished by NMR spectroscopic and mass-spectrometric studies, and the biosyntheses of compounds 1, 5, and 6 were investigated by feeding experiments with (13)C-labeled precursors. All results indicate a biogenetic sequence with metabolite 5 and sarkomycin (7) as precursors in the formation of spirocyclus 1 through an intermolecular Diels-Alder-type reaction.

Nocardichelins A and B, siderophores from Nocardia strain acta 3026

An actinomycete, strain Acta 3026, isolated from mangrove soil was characterized and found to belong to the genus Nocardia. The strain produces two new cytotoxic metabolites, nocardichelins A (1) and B (2). Each of the compounds strongly inhibited human cell lines from gastric adenocarcinoma, breast carcinoma, and hepatocellular carcinoma with GI50 values in a low micromolar to nanomolar range. The structural characterization of the compounds was performed by mass spectrometry and NMR spectroscopy. The nocardichelins represent a new group of siderophores that combine the structural elements of mycobactin-type siderophores from mycobacteria and hydroxamate-type siderophores (desferrioxamine B) produced by streptomycetes. The chromazurol S assay, characteristic for iron(III) complexation, was positive, confirming the role as a siderophore.

Abyssomicins G and H and atrop-Abyssomicin C from the Marine Verrucosispora Strain AB-18-032†

Abyssomicin C is a complex polyketide-type antibiotic and the first natural inhibitor of the p-aminobenzoate biosynthesis produced by the marine Verrucosispora strain AB-18-032. We have now isolated three novel naturally produced abyssomicins, among them the even more active atrop-abyssomicin C. The chemical structures were elucidated by mass spectrometry and NMR spectroscopy.

Elloxazinones A and B, New Aminophenoxazinones from Streptomyces griseus Acta 2871†

Two new aminophenoxazinone compounds with antitumor activity, elloxazinone A and B, were isolated from the culture filtrate of Streptomyces griseus Acta 2871. Their chemical structures were determined by mass spectrometry, NMR spectroscopy and X-ray analysis. Elloxazinones A and B showed a moderate inhibition of the proliferation of human cells from gastric adenocarcinoma in vitro but a strong inhibition of hepatocellular carcinoma cells whereas elloxazinone B strongly inhibited the proliferation of human breast carcinoma cells.

Fluostatins C-E, novel members of the fluostatin family produced by Streptomyces strain Acta 1383

Three new members of the fluostatin family, fluostatins C-E, were discovered in a culture filtrate extract of strain Acta 1383 during an HPLC screening program. The producing strain belongs to the genus Streptomyces and is closely related to type strains classified in the Streptomyces lavendulae 16S rRNA subclade. Fluostatins are named by their characteristic fluorenone chromophore. Fluostatin C shows moderate activity against selected human tumor cell lines.

Different polyketide folding modes converge to an identical molecular architecture

Metabolic diversity is being studied intensively by evolutionary biologists, but so far there has been no comparison of biosynthetic pathways leading to a particular secondary metabolite in both prokaryotes and eukaryotes. We have detected the bioactive anthraquinone chrysophanol, which serves as a chemical defense in diverse eukaryotic organisms, in a bacterial Nocardia strain, thereby permitting the first comparative biosynthetic study. Two basic modes of folding a polyketide chain to fused-ring aromatic structures have so far been described: mode F (referring to fungi) and mode S (from Streptomyces). We have demonstrated that in eukaryotes (fungi, higher plants and insects), chrysophanol is formed via folding mode F. In actinomycetes, by contrast, the cyclization follows mode S. Thus, chrysophanol is the first polyketide synthase product that is built up by more than one polyketide folding mode.

Auxofuran, a novel metabolite that stimulates the growth of fly agaric, is produced by the mycorrhiza helper bacterium Streptomyces strain AcH 505

The mycorrhiza helper bacterium Streptomyces strain AcH 505 improves mycelial growth of ectomycorrhizal fungi and formation of ectomycorrhizas between Amanita muscaria and spruce but suppresses the growth of plant-pathogenic fungi, suggesting that it produces both fungal growth-stimulating and -suppressing compounds. The dominant fungal-growth-promoting substance produced by strain AcH 505, auxofuran, was isolated, and its effect on the levels of gene expression of A. muscaria was investigated. Auxofuran and its synthetic analogue 7-dehydroxy-auxofuran were most effective at a concentration of 15 microM, and application of these compounds led to increased lipid metabolism-related gene expression. Cocultivation of strain AcH 505 and A. muscaria stimulated auxofuran production by the streptomycete. The antifungal substances produced by strain AcH 505 were identified as the antibiotics WS-5995 B and C. WS-5995 B completely blocked mycelial growth at a concentration of 60 microM and caused a cell stress-related gene expression response in A. muscaria. Characterization of these compounds provides the foundation for molecular analysis of the fungus-bacterium interaction in the ectomycorrhizal symbiosis between fly agaric and spruce.

Fogacin, a Novel Cyclic Octaketide Produced by Streptomyces Strain Tü 6319

A new octaketide named fogacin (1) was isolated from Streptomyces sp. (strain Tü 6319). Furthermore two shunt metabolites, SEK4b (2) and anhydroSEK4b (3), were detected and identified as non-enzymatically cyclized products of polyketide intermediates built during the biosynthesis of actinorhodin. SEK4b (2) as well as anhydroSEK4b (3) were previously described as metabolites of genetically engineered strains.