Myxopyronins (MXN) and corallopyronins (COR) are structurally related α-pyrone antibiotics from myxobacteria that represent a highly promising compound class for the development of broad-spectrum ...antibacterial therapeutic agents. Their ability to inhibit RNA polymerase through interaction with the “switch region”, a novel target, distant from previously characterized RNA polymerase inhibitors (e.g. rifampicin), makes them particularly promising candidates for further research. To improve compound supply for further investigation of MXN, COR and novel derivatives of these antibacterial agents, establishment of an efficient and versatile microbial production platform for myxobacterial α-pyrone antibiotics is highly desirable. Here we describe design, construction and expression of a heterologous production and engineering platforms for MXN and COR to facilitate rational structure design and yield improvement approaches in the myxobacterial host strain Myxococcus xanthus DK1622. Optimization of the cultivation medium yielded significantly higher production titers of MXN A at around 41-fold increase and COR A at around 25-fold increase, compared to the standard CTT medium.
•myxopyronin gene cluster cloned, modified and expressed in heterologous host.•myxopyronin/corallopyronin hybrid gene cluster expressed in heterologous host.•Production of respective metabolites by heterologous producer confirmed.•Production medium optimized for both heterologous producers.•Production yield of both metabolites significantly increased.
Myxopyronins and corallopyronins are structurally related α-pyrone antibiotics from myxobacteria. They are thought to represent a highly promising compound class for the development of broad-spectrum ...antibacterial therapeutic agents, because of their ability to inhibit RNA polymerase through interaction with the "switch region", a recently identified novel drug target. Here we describe the identification and characterization of the myxopyronin biosynthetic pathway from Myxococcus fulvus Mx f50. A detailed comparison with the recently identified corallopyronin biosynthetic pathway revealed the genetic and biochemical basis, thus explaining the observed structural differences between the two natural product families. Directed mutagenesis procedures for M. fulvus Mx f50 were developed to enable functional studies and pathway modifications. Our work provided new insights into myxopyronin biosynthesis and led to the production of a novel and unexpected myxopyronin derivative.
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In this study, PVD Ru–Mn composites were investigated in terms of major concerns that arise with the introduction of a new type of barrier. First, the Cu diffusion barrier ...performance after annealing at 600°C and under subsequent BTS of +2MV/cm, 250°C was investigated on SiO2, and after 350°C annealing on low-k dielectrics. Ru–Mn films proved to serve as outstanding Cu diffusion barrier over a wide range of Mn content. Second, the origin of the barrier performance was investigated using TEM, EELS and XPS depth profiling techniques, revealing the stuffing of grain boundaries as barrier mechanism. Third, Cu plating on damascene wafers applying a Ru–Mn seed layer was tested, and also the Cu adhesion thereon, resulting in a complete feature fill and excellent Cu wetting behavior. Fourth, the blocking of oxygen diffusion was examined, leading to a performance comparable to PVD TaN. Finally, the Mn content inside Ru was reduced down to 1at.% without compromising the superior material properties.
Members of the Roseobacter clade are abundant and widespread in marine habitats and have very diverse metabolisms. Production of acylated homoserine lactones (AHL) and secondary metabolites, e.g., ...antibiotics has been described sporadically. This prompted us to screen 22 strains of this group for production of signaling molecules, antagonistic activity against bacteria of different phylogenetic groups, and the presence of genes encoding for nonribosomal peptide synthetases (NRPS) and polyketide synthases (PKS), representing enzymes involved in the synthesis of various pharmaceutically important natural products. The screening approach for NRPS and PKS genes was based on polymerase chain reaction (PCR) with degenerate primers specific for conserved sequence motifs. Additionally, sequences from whole genome sequencing projects of organisms of the Roseobacter clade were considered. Obtained PCR products were cloned, sequenced, and compared with genes of known function. With the PCR approach genes showing similarity to known NRPS and PKS genes were found in seven and five strains, respectively, and three PKS and NRPS sequences from genome sequencing projects were obtained. Three strains exhibited antagonistic activity and also showed production of AHL. Overall production of AHL was found in 10 isolates. Phylogenetic analysis of the 16S rRNA gene sequences of the tested organisms showed that several of the AHL-positive strains clustered together. Three strains were positive for three or four categories tested, and were found to be closely related within the genus Phaeobacter. The presence of a highly similar hybrid PKS/NRPS gene locus of unknown function in sequenced genomes of the Roseobacter clade plus the significant similarity of gene fragments from the strains studied to these genes argues for the functional requirement of the encoded hybrid PKS/NRPS complex. Our screening results therefore suggest that the Roseobacter clade is indeed employing PKS/NRPS biochemistry and should thus be further studied as a potential and largely untapped source of secondary metabolites.
Kendomycin is a bioactive polyketide that is produced by various Streptomyces strains. It displays strong antibiotic activities against a wide range of bacteria and exhibits remarkable cytotoxic ...effects on the growth of several human cancer cell lines. In this study we cloned the corresponding biosynthetic locus from the producer Streptomyces violaceoruber (strain 3844-33C). Our analysis shows that a mixed type I/type III polyketide synthase pathway is responsible for the formation of the fully carbogenic macrocyclic scaffold of kendomycin, which is unprecedented among all of the ansa compounds that have been isolated so far. Heterologous expression of a gene set in Streptomyces coelicolor shows that 3,5-dihydroxybenzoic acid is an intermediate in the starter unit biosynthesis that is initiated by the type III polyketide synthase. The identification of the kendomycin biosynthetic gene cluster sets the stage to study a novel chain termination mechanism by a type I PKS that leads to carbocycle formation and provides the starting material for the heterologous expression of the entire pathway, and the production of novel derivatives by genetic engineering.
The structurally unique leupyrrins A1 (1), A2 (2), B1 (3), B2 (4), C (5), and D (6) were isolated as one of three groups of secondary metabolites from Sorangium cellulosum strains So ce705 and So ...ce690. An unusually substituted gamma-butyrolactone ring and pyrrole and oxazoline rings are embedded in a nonsymmetric macrodiolide core structure, giving rise to compounds 1-6 as members of a novel class of secondary metabolites. Leupyrrin A1 (1) shows good biological activity against various fungi and eukaryotic cells.
Gasifiers are containment vessels used to react a carbon feedstock with oxygen and water in order to produce synthetic gas. During the gasification process the refractory liner protects the gasifier ...shell from high temperatures and pressures, corrosive slag, thermal shock and thermal cycling. However the performance of the currently used high chrome oxide materials does not meet the service requirements of industry, so there is a demand of new chrome oxide free materials. Compared to the sintering atmosphere the mechanical properties, phase formation as well as the resistance against thermal shock and alkali-corrosion of shaped alumina based refractories have been evaluated. According to the results potential candidates for further studies including reducing sintered β-alumina, spinel, hibonite and slag-stone.
Big effects from small changes: In a comparative analysis of the nonribosomal peptide synthetases (NRPSs) from the biosynthetic pathways of two highly related myxobacterial lipopeptides, module ...skipping and point mutations are directly correlated to structural variations in these natural products. The skipping process during myxochromide S biosynthesis was characterized biochemically and represents the first example of a module skipping in NRPS systems.
To improve teaching in higher education, teachers in psychology are encouraged to use evidence-based teaching, that is, to apply empirical findings regarding learning and teaching, when designing ...learning opportunities. This report illustrates the combination of evidence-based teaching and the Scholarship of Teaching and Learning in teaching psychology and describes the implementation of an innovative module for first-year students in the undergraduate psychology program at Goethe University Frankfurt, Germany, as an example. A detailed description of the teaching formats is provided with a focus on evidence-based teaching techniques, which were implemented in the first semester of the module, specifically feedback, testing effects, and spaced learning. Furthermore, evaluation data concerning the students’ perceptions and objective assessments are presented as an example of the Scholarship of Teaching and Learning. For example, students significantly acquired knowledge during web-based training, but the learning outcomes are independent of their pretest knowledge, suggesting that this teaching format may contribute to the reduction of heterogeneity among first-year students. Possible implications for future modifications of the module are discussed and general recommendations are offered to teachers of psychology regarding the implementation of a combination of evidence-based teaching and the Scholarship of Teaching and Learning to promote empirically founded teaching.
Polyunsaturated fatty acids (PUFAs), particularly the omega-3 long-chain PUFAs (LC-PUFAs) eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are well known for their beneficial health ...effects. The obvious limitation of the present EPA/DHA key source, fish oil, demands for alternative and sustainable PUFA resources and several biotechnological approaches addressing this problem are currently under development. Different marine microorganisms are known to produce PUFAs de novounder strictly anaerobic conditions employing polyketide synthase (PKS)-like enzymes known as PUFA synthases. Here, we report for the first time the characterization of such PUFA synthases from terrestrial origin. Two distinct types of PUFA biosynthetic gene clusters were discovered, originating from linoleic acid producing myxobacteria of the genus Sorangiumas well as from species of the recently discovered myxobacterial genus Aetherobacter, that turned out to be prolific producers of EPA and DHA. The identified biosynthetic pathways differ significantly from the marine systems in terms of gene organization, catalytic domain arrangement, and sequence identity of the encoded PUFA synthases. Notably, a unique domain, which most likely acts as 1-acylglycerol-3-phosphate O-acyltransferase, was identified in these myxobacterial PUFA synthases. As the native producer strains grow slowly, are difficult to handle, and genetic modification has proven difficult, synthetic biotechnology approaches were applied to establish a heterologous production platform in the myxobacterial model strain Myxococcus xanthus.
