Pattern Formation in the Bromate–Sulfite–Ferrocyanide Reaction

Mixed Landolt-type pH oscillators are versatile systems that allow the experimental study of a wide range of nonlinear phenomena including multistability, oscillations, and spatiotemporal patterns. We report on the dynamics of the bromate–sulfite–ferrocyanide reaction operated in a open one-side-fed reactor, where spatial bistability, spatiotemporal oscillations, front and Turing-type patterns have been observed. The role of different experimental parameters, like the input flow concentrations of the hydrogen and the ferrocyanide ions, the temperature and the thickness of the gel medium (which affects the rate of the diffusive feed) have been investigated. We point out that all these parameters can be efficiently used to control the spatiotemporal dynamics. We show that the increase of ionic strength stabilizes the uniform states at the expense of the patterned one. Some general aspects of the spatiotemporal dynamics of mixed Landolt type systems, which are based on the oxidation of sulfite ions by strong oxidants, are emphasized

Pattern Formation in the Bromate–Sulfite–Ferrocyanide Reaction

Mixed Landolt-type pH oscillators are versatile systems that allow the experimental study of a wide range of nonlinear phenomena including multistability, oscillations, and spatiotemporal patterns. We report on the dynamics of the bromate–sulfite–ferrocyanide reaction operated in a open one-side-fed reactor, where spatial bistability, spatiotemporal oscillations, front and Turing-type patterns have been observed. The role of different experimental parameters, like the input flow concentrations of the hydrogen and the ferrocyanide ions, the temperature and the thickness of the gel medium (which affects the rate of the diffusive feed) have been investigated. We point out that all these parameters can be efficiently used to control the spatiotemporal dynamics. We show that the increase of ionic strength stabilizes the uniform states at the expense of the patterned one. Some general aspects of the spatiotemporal dynamics of mixed Landolt type systems, which are based on the oxidation of sulfite ions by strong oxidants, are emphasized

Insights into the Biosynthesis of 12-Membered Resorcylic Acid Lactones from Heterologous Production in <i>Saccharomyces cerevisiae</i>

The phytotoxic fungal polyketides lasiodiplodin and resorcylide inhibit human blood coagulation factor XIIIa, mineralocorticoid receptors, and prostaglandin biosynthesis. These secondary metabolites belong to the 12-membered resorcylic acid lactone (RAL₁₂) subclass of the benzenediol lactone (BDL) family. Identification of genomic loci for the biosynthesis of lasiodiplodin from <i>Lasiodiplodia theobromae</i> and resorcylide from <i>Acremonium zeae</i> revealed collaborating iterative polyketide synthase (iPKS) pairs whose efficient heterologous expression in <i>Saccharomyces cerevisiae</i> provided a convenient access to the RAL₁₂ scaffolds desmethyl-lasiodiplodin and <i>trans</i>-resorcylide, respectively. Lasiodiplodin production was reconstituted in the heterologous host by co-expressing an <i>O</i>-methyltransferase also encoded in the lasiodiplodin cluster, while a glutathione-<i>S</i>-transferase was found not to be necessary for heterologous production. Clarification of the biogenesis of known resorcylide congeners in the heterologous host helped to disentangle the roles that biosynthetic irregularities and chemical interconversions play in generating chemical diversity. Observation of 14-membered RAL homologues during <i>in vivo</i> heterologous biosynthesis of RAL₁₂ metabolites revealed “stuttering” by fungal iPKSs. The close global and domain-level sequence similarities of the orthologous BDL synthases across different structural subclasses implicate repeated horizontal gene transfers and/or cluster losses in different fungal lineages. The absence of straightforward correlations between enzyme sequences and product structural features (the size of the macrocycle, the conformation of the exocyclic methyl group, or the extent of reduction by the hrPKS) suggest that BDL structural variety is the result of a select few mutations in key active site cavity positions

Diversity-Oriented Combinatorial Biosynthesis of Hybrid Polyketide Scaffolds from Azaphilone and Benzenediol Lactone Biosynthons

Two disparate polyketide families, the benzenediol lactones and the azaphilones, are produced by fungi using iterative polyketide synthase (iPKS) enzymes consisting of collaborating partner subunits. Exploitation of this common biosynthetic logic using iPKS subunit shuffling allowed the diversity-oriented combinatorial biosynthesis of unprecedented polyketide scaffolds new to nature, bearing structural motifs from both of these orthogonal natural product families. Starter unit acyltransferase domain replacements proved necessary but not sufficient to guarantee communication between iPKS subunits

Biosynthesis of Cytosporones in Leotiomycetous Filamentous Fungi

Polyketides with the isochroman-3-one pharmacophore are rare among fungal natural products as their biosynthesis requires an unorthodox S-type aromatic ring cyclization. Genome mining uncovered a conserved gene cluster in select leotiomycetous fungi that encodes the biosynthesis of cytosporones, including isochroman-3-one congeners. Combinatorial biosynthesis in total biosynthetic and biocatalytic formats in Saccharomyces cerevisiae and in vitro reconstitution of key reactions with purified enzymes revealed how cytosporone structural and bioactivity diversity is generated. The S-type acyl dihydroxyphenylacetic acid (ADA) core of cytosporones is assembled by a collaborating polyketide synthase pair. Thioesterase domain-catalyzed transesterification releases ADA esters, some of which are known Nur77 modulators. Alternatively, hydrolytic release allows C6 hydroxylation by a flavin-dependent monooxygenase, yielding a trihydroxybenzene moiety. Reduction of the C9 carbonyl by a short chain dehydrogenase/reductase initiates isochroman-3-one formation, affording cytosporones with cytotoxic and antimicrobial activity. Enoyl di- or trihydroxyphenylacetic acids are generated as shunt products, while isocroman-3,4-diones are formed by autoxidation. The cytosporone pathway offers novel polyketide biosynthetic enzymes for combinatorial synthetic biology to advance the production of “unnatural” natural products for drug discovery