Structural progression of amyloid-ß Arctic mutant aggregation in cells revealed by multiparametric imaging.

The 42-amino-acid ß-amyloid (Aß42) is a critical causative agent in the pathology of Alzheimer's disease. The hereditary Arctic mutation of Aß42 (E22G) leads to increased intracellular accumulation of ß-amyloid in early-onset Alzheimer's disease. However, it remains largely unknown how the Arctic mutant variant leads to aggressive protein aggregation and increased intracellular toxicity. Here, we constructed stable cell lines expressing fluorescent-tagged wildtype (WT) and E22G Aß42 to study the aggregation kinetics of the Arctic Aß42 mutant peptide and its heterogeneous structural forms. Arctic-mutant peptides assemble and form fibrils at a much faster rate than WT peptides. We identified five categories of intracellular aggregate-oligomers, single fibrils, fibril bundles, clusters, and aggresomes-that underline the heterogeneity of these Aß42 aggregates and represent the progression of Aß42 aggregation within the cell. Fluorescence-lifetime imaging (FLIM) and 3D structural illumination microscopy (SIM) showed that all aggregate species displayed highly compact structures with strong affinity between individual fibrils. We also found that aggregates formed by Arctic mutant Aß42 were more resistant to intracellular degradation than their WT counterparts. Our findings uncover the structural basis of the progression of Arctic mutant Aß42 aggregation in the cell.

Substrate Flexibility of the Flavin-Dependent Dihydropyrrole Oxidases PigB and HapB Involved in Antibiotic Prodigiosin Biosynthesis.

In the biosynthesis of the tripyrrolic pigment prodigiosin, PigB is a predicted flavin-dependent oxidase responsible for the formation of 2-methyl-3-amylpyrrole (MAP) from a dihydropyrrole. To prove which dihydropyrrole is the true intermediate, both possibilities, 5-methyl-4-pentyl-3,4-dihydro-2H-pyrrole (5 a, resulting from transamination of the aldehyde of 3-acetyloctanal) and 2-methyl-3-pentyl-3,4-dihydro-2H-pyrrole (6, resulting from transamination of the ketone), were synthesised. Only 5 a restored pigment production in a strain of Serratia sp. ATCC 39006 blocked earlier in MAP biosynthesis. PigB is membrane-associated and inactive when its transmembrane domain was deleted, but HapB, its homologue in Hahella chejuensis, lacks the transmembrane domain and is active in solution. Two colourimetric assays for PigB and HapB were developed, and the HapB-catalysed reaction was kinetically characterised. Ten analogues of 5 a were synthesised, varying in the C2 and C3 side chains, and tested as substrates of HapB in vitro and for restoration of pigment production in Serratia ΔpigD in vivo. All lengths of side chain tested at C3 were accepted, but only short side chains at C2 were accepted. The knowledge that 5 a is an intermediate in prodigiosin biosynthesis and the ease of synthesis of analogues of 5 a makes a range of prodigiosin analogues readily available by mutasynthesis.

CRISPR-Cas gene-editing reveals RsmA and RsmC act through FlhDC to repress the SdhE flavinylation factor and control motility and prodigiosin production in Serratia.

SdhE is required for the flavinylation and activation of succinate dehydrogenase and fumarate reductase (FRD). In addition, SdhE is conserved in proteobacteria (α, ß and γ) and eukaryotes. Although the function of this recently characterized family of proteins has been determined, almost nothing is known about how their genes are regulated. Here, the RsmA (CsrA) and RsmC (HexY) post-transcriptional and post-translational regulators have been identified and shown to repress sdhEygfX expression in Serratia sp. ATCC 39006. Conversely, the flagella master regulator complex, FlhDC, activated sdhEygfX transcription. To investigate the hierarchy of control, we developed a novel approach that utilized endogenous CRISPR (clustered regularly interspaced short palindromic repeats)-Cas (CRISPR associated) genome-editing by a type I-F system to generate a chromosomal point mutation in flhC. Mutation of flhC alleviated the ability of RsmC to repress sdhEygfX expression, whereas RsmA acted in both an FlhDC-dependent and -independent manner to inhibit sdhEygfX. Mutation of rsmA or rsmC, or overexpression of FlhDC, led to increased prodigiosin, biosurfactant, swimming and swarming. Consistent with the modulation of sdhE by motility regulators, we have demonstrated that SdhE and FRD are required for maximal flagella-dependent swimming. Together, these results demonstrate that regulators of both metabolism and motility (RsmA, RsmC and FlhDC) control the transcription of the sdhEygfX operon.

Expression-level dependent perturbation of cell proteostasis and nuclear morphology by aggregation-prone polyglutamine proteins.

We describe a gene expression system for use in mammalian cells that yields reproducible, inducible gene expression that can be modulated within the physiological range. A synthetic promoter library was generated from which representatives were selected that gave weak, intermediate-strength or strong promoter activity. Each promoter resulted in a tight expression range when used to drive single-copy reporter genes integrated at the same genome location in stable cell lines, in contrast to the broad range of expression typical of transiently transfected cells. To test this new expression system in neurodegenerative disease models, we used each promoter type to generate cell lines carrying single-copy genes encoding polyglutamine-containing proteins. Expression over a period of up to three months resulted in a proportion of cells developing juxtanuclear aggresomes whose rate of formation, penetrance, and morphology were expression-level dependent. At the highest expression levels, fibrillar aggregates deposit close to the nuclear envelope, indicating that cell proteostasis is overwhelmed by misfolded protein species. We also observed expression-level dependent, abnormal nuclear morphology in cells containing aggresomes, with up to ∼80% of cells affected. This system constitutes a valuable tool in gene regulation at different levels and allows the quantitative assessment of gene expression effects when developing disease models or investigating cell function through the introduction of gene constructs.

A quorum-sensing molecule acts as a morphogen controlling gas vesicle organelle biogenesis and adaptive flotation in an enterobacterium.

Gas vesicles are hollow intracellular proteinaceous organelles produced by aquatic Eubacteria and Archaea, including cyanobacteria and halobacteria. Gas vesicles increase buoyancy and allow taxis toward air-liquid interfaces, enabling subsequent niche colonization. Here we report a unique example of gas vesicle-mediated flotation in an enterobacterium; Serratia sp. strain ATCC39006. This strain is a member of the Enterobacteriaceae previously studied for its production of prodigiosin and carbapenem antibiotics. Genes required for gas vesicle synthesis mapped to a 16.6-kb gene cluster encoding three distinct homologs of the main structural protein, GvpA. Heterologous expression of this locus in Escherichia coli induced copious vesicle production and efficient cell buoyancy. Gas vesicle morphogenesis in Serratia enabled formation of a pellicle-like layer of highly vacuolated cells, which was dependent on oxygen limitation and the expression of ntrB/C and cheY-like regulatory genes within the gas-vesicle gene cluster. Gas vesicle biogenesis was strictly controlled by intercellular chemical signaling, through an N-acyl homoserine lactone, indicating that in this system the quorum-sensing molecule acts as a morphogen initiating organelle development. Flagella-based motility and gas vesicle morphogenesis were also oppositely regulated by the small RNA-binding protein, RsmA, suggesting environmental adaptation through physiological control of the choice between motility and flotation as alternative taxis modes. We propose that gas vesicle biogenesis in this strain represents a distinct mechanism of mobility, regulated by oxygen availability, nutritional status, the RsmA global regulatory system, and the quorum-sensing morphogen.

A metabolic regulator modulates virulence and quorum sensing signal production in Pectobacterium atrosepticum.

Plant cell wall-degrading enzymes (PCWDE) are key virulence determinants in the pathogenesis of the potato pathogen Pectobacterium atrosepticum. In this study, we report the impact on virulence of a transposon insertion mutation in the metJ gene that codes for the repressor of the methionine biosynthesis regulon. In a mutant strain defective for the small regulatory RNA rsmB, PCWDE are not produced and virulence in potato tubers is almost totally abolished. However, when the metJ gene is disrupted in this background, the rsmB(-) phenotype is suppressed and virulence and PCWDE production are restored. Additionally, when metJ is disrupted, production of the quorum-sensing signal, N-(3-oxohexanoyl)-homoserine lactone, is increased. The metJ mutant strains showed pleiotropic transcriptional impacts affecting approximately a quarter of the genome. Genes involved in methionine biosynthesis were most highly upregulated but many virulence-associated transcripts were also upregulated. This is the first report of the impact of the MetJ repressor on virulence in bacteria.

RNA-seq reveals the RNA binding proteins, Hfq and RsmA, play various roles in virulence, antibiotic production and genomic flux in Serratia sp. ATCC 39006.

BACKGROUND: Serratia sp. ATCC 39006 (S39006) is a Gram-negative enterobacterium that is virulent in plant and animal models. It produces a red-pigmented trypyrrole secondary metabolite, prodigiosin (Pig), and a carbapenem antibiotic (Car), as well as the exoenzymes, pectate lyase and cellulase. Secondary metabolite production in this strain is controlled by a complex regulatory network involving quorum sensing (QS). Hfq and RsmA (two RNA binding proteins and major post-transcriptional regulators of gene expression) play opposing roles in the regulation of several key phenotypes within S39006. Prodigiosin and carbapenem production was abolished, and virulence attenuated, in an S39006 ∆hfq mutant, while the converse was observed in an S39006 rsmA transposon insertion mutant. RESULTS: In order to define the complete regulon of Hfq and RsmA, deep sequencing of cDNA libraries (RNA-seq) was used to analyse the whole transcriptome of S39006 ∆hfq and rsmA::Tn mutants. Moreover, we investigated global changes in the proteome using an LC-MS/MS approach. Analysis of differential gene expression showed that Hfq and RsmA directly or indirectly regulate (at the level of RNA) 4% and 19% of the genome, respectively, with some correlation between RNA and protein expression. Pathways affected include those involved in antibiotic regulation, virulence, flagella synthesis, and surfactant production. Although Hfq and RsmA are reported to activate flagellum production in E. coli and an adherent-invasive E. coli hfq mutant was shown to have no flagella by electron microscopy, we found that flagellar production was increased in the S39006 rsmA and hfq mutants. Additionally, deletion of rsmA resulted in greater genomic flux with increased activity of two mobile genetic elements. This was confirmed by qPCR and analysis of rsmA culture supernatant revealed the presence of prophage DNA and phage particles. Finally, expression of a hypothetical protein containing DUF364 increased prodigiosin production and was controlled by a putative 5' cis-acting regulatory RNA element. CONCLUSION: Using a combination of transcriptomics and proteomics this study provides a systems-level understanding of Hfq and RsmA regulation and identifies similarities and differences in the regulons of two major regulators. Additionally our study indicates that RsmA regulates both core and variable genome regions and contributes to genome stability.

The RNA chaperone, Hfq, controls two luxR-type regulators and plays a key role in pathogenesis and production of antibiotics in Serratia sp. ATCC 39006.

Serratia sp. ATCC 39006 (S39006) is a Gram-negative bacterium that is virulent in plant (potato) and animal (Caenorhabditis elegans) models. It produces two secondary metabolite antibiotics, a prodigiosin and a carbapenem, and the exoenzymes, pectate lyase and cellulase. A complex regulatory network that includes quorum sensing (QS) controls production of prodigiosin. While many aspects of the regulation of the metabolites and exoenzymes are well understood, the potential role in this network of the RNA chaperone Hfq and dependent small regulatory RNAs has not been characterized. Hfq is an RNA chaperone involved in post-transcriptional regulation that plays a key role in stress response and virulence in diverse bacterial species. To explore whether Hfq-dependent processes might contribute to the regulation of antibiotic production we constructed an S39006 Δhfq mutant. Production of prodigiosin and carbapenem was abolished in this mutant strain, while production of the QS signalling molecule, butanoyl homoserine lactone (BHL), was unaffected. Using transcriptional fusions, we found that Hfq regulates the QS response regulators, SmaR and CarR. Additionally, exoenzyme production and swimming motility were decreased in a Δhfq mutant, and virulence was attenuated in potato and C. elegans models. These results suggest that an Hfq-dependent pathway is involved in the regulation of virulence and secondary metabolite production in S39006.

Quorum sensing-controlled Evr regulates a conserved cryptic pigment biosynthetic cluster and a novel phenomycin-like locus in the plant pathogen, Pectobacterium carotovorum.

Pectobacterium carotovorum SCRI193 is a phytopathogenic Gram-negative bacterium. In this study, we have identified a novel cryptic pigment biosynthetic locus in P. carotovorum SCRI193 which we have called the Pectobacterium orange pigment (pop) cluster. The pop cluster is flanked by two tRNA genes and contains genes that encode non-ribosomal peptide synthases and polyketide synthase and produces a negatively charged polar orange pigment. Orange pigment production is activated when an adjacent transcriptional activator sharing sequence similarity with the Erwinia virulence regulator (Evr) is overexpressed. Evr was shown to positively activate its own transcription and that of the pigment biosynthetic genes and an unlinked locus encoding a phenomycin homologue. In addition, the expression of Evr and orange pigment production was shown to be regulated by N-(3-oxohexanoyl)-HSL (OHHL) quorum sensing and have a virulence phenotype in potato. Finally, by comparative genomics and Southern blotting we demonstrate that this pigment biosynthetic cluster is present in multiple P. carotovorum spp., Pectobacterium brasiliensis 1692 and a truncated version of the cluster is present in Pectobacterium atrosepticum. The conserved nature of this cluster in P. carotovorum and P. brasiliensis suggests that the pop cluster has an important function in these broad-host-range soft rotting bacteria, which is no longer required in the narrow-host-range P. atrosepticum SCRI1043.

The PhoBR two-component system regulates antibiotic biosynthesis in Serratia in response to phosphate.

BACKGROUND: Secondary metabolism in Serratia sp. ATCC 39006 (Serratia 39006) is controlled via a complex network of regulators, including a LuxIR-type (SmaIR) quorum sensing (QS) system. Here we investigate the molecular mechanism by which phosphate limitation controls biosynthesis of two antibiotic secondary metabolites, prodigiosin and carbapenem, in Serratia 39006. RESULTS: We demonstrate that a mutation in the high affinity phosphate transporter pstSCAB-phoU, believed to mimic low phosphate conditions, causes upregulation of secondary metabolism and QS in Serratia 39006, via the PhoBR two-component system. Phosphate limitation also activated secondary metabolism and QS in Serratia 39006. In addition, a pstS mutation resulted in upregulation of rap. Rap, a putative SlyA/MarR-family transcriptional regulator, shares similarity with the global regulator RovA (regulator of virulence) from Yersina spp. and is an activator of secondary metabolism in Serratia 39006. We demonstrate that expression of rap, pigA-O (encoding the prodigiosin biosynthetic operon) and smaI are controlled via PhoBR in Serratia 39006. CONCLUSION: Phosphate limitation regulates secondary metabolism in Serratia 39006 via multiple inter-linked pathways, incorporating transcriptional control mediated by three important global regulators, PhoB, SmaR and Rap.

The rsmS (ybaM) mutation causes bypass suppression of the RsmAB post-transcriptional virulence regulation system in enterobacterial phytopathogens.

Plant cell wall degrading enzymes (PCWDEs) are the primary virulence determinants of soft rotting bacteria such as the potato pathogen, Pectobacterium atrosepticum. The regulation of secondary metabolite (Rsm) system controls production of PCWDEs in response to changing nutrient conditions. This work identified a new suppressor of an rsmB mutation - ECA1172 or rsmS (rsmB suppressor). Mutants defective in rsmB (encoding a small regulatory RNA), show reduced elaboration of the quorum sensing molecule (N-3-oxohexanoyl-homoserine lactone; OHHL) and PCWDEs. However, OHHL and PCWDE production were partially restored in an rsmB, rsmS double mutant. Single rsmS mutants, overproduced PCWDEs and OHHL relative to wild type P. atrosepticum and exhibited hypervirulence in potato. RsmS overproduction also resulted in increased PCWDEs and OHHL. Homology searches revealed rsmS conservation across pathogens such as Escherichia coli (ybaM), Dickeya solani, Klebsiella pneumoniae and Shigella flexneri. An rsmS mutant of Pectobacterium carotovorum ATCC39048 showed bypass of rsmB-dependent repression of PCWDEs and OHHL production. P. carotovorum ATCC39048 produces the ß-lactam antibiotic, 1-carbapen-2-em-3-carboxylic acid (a carbapenem). Production of the antibiotic was repressed in an rsmB mutant but partially restored in an rsmB, rsmS double mutant. This work highlights the importance of RsmS, as a conserved pleiotropic regulator of virulence and antibiotic biosynthesis.

Integrated regulation involving quorum sensing, a two-component system, a GGDEF/EAL domain protein and a post-transcriptional regulator controls swarming and RhlA-dependent surfactant biosynthesis in Serratia.

Serratia sp. ATCC 39006 (Serratia 39006) is a Gram-negative bacterium which produces the secondary metabolite antibiotics, prodigiosin and 1-carbapen-2-em-3-carboxylic acid and secretes plant cell wall degrading enzymes. In this study we have identified mutations in the genes, pigX, rap and rsmA, which caused increased production of a previously unidentified surfactant and flagella-dependent swarming phenotype in Serratia 39006. Analysis of both the biosynthesis and regulation of surfactant production and swarming, revealed FlhC, quorum sensing, a GGDEF/EAL domain protein (PigX), a GacAS two-component system, an Rsm system and Rap as key regulators. In addition, surfactant biosynthesis required a protein similar to RhlA, involved in rhamnolipid synthesis in Pseudomonas aeruginosa. Homologues of RhlA have not previously been identified in members of the Enterobacteriaceae. Furthermore, we provide evidence that the surfactant may be responsible for dispersal of the antimicrobial pigment, prodigiosin. This study demonstrates the complex regulatory inputs into the coordinated multicellular swarming phenotype in Serratia.

Chemoenzymatic synthesis of prodigiosin analogues--exploring the substrate specificity of PigC.

Analogues of prodigiosin, a tripyrrolic pigment produced by Serratia species with potent immunosuppressive and anticancer activities, have been produced by feeding synthetic analogues of the normal precursor MBC to mutants of Serratia sp. ATCC 39006 or to engineered strains of Escherichia coli; in this way it has been shown that the prodigiosin synthesising enzyme, PigC, has a relaxed substrate-specificity.

A Plasmid-Transposon Hybrid Mutagenesis System Effective in a Broad Range of Enterobacteria.

Random transposon mutagenesis is a powerful technique used to generate libraries of genetic insertions in many different bacterial strains. Here we develop a system facilitating random transposon mutagenesis in a range of different Gram-negative bacterial strains, including Pectobacterium atrosepticum, Citrobacter rodentium, Serratia sp. ATCC39006, Serratia plymuthica, Dickeya dadantii, and many more. Transposon mutagenesis was optimized in each of these strains and three studies are presented to show the efficacy of this system. Firstly, the important agricultural pathogen D. dadantii was mutagenized. Two mutants that showed reduced protease production and one mutant producing the previously cryptic pigment, indigoidine, were identified and characterized. Secondly, the enterobacterium, Serratia sp. ATCC39006 was mutagenized and mutants incapable of producing gas vesicles, proteinaceous intracellular organelles, were identified. One of these contained a ß-galactosidase transcriptional fusion within the gene gvpA1, essential for gas vesicle production. Finally, the system was used to mutate the biosynthetic gene clusters of the antifungal, anti-oomycete and anticancer polyketide, oocydin A, in the plant-associated enterobacterium, Dickeya solani MK10. The mutagenesis system was developed to allow easy identification of transposon insertion sites by sequencing, after facile generation of a replicon encompassing the transposon and adjacent DNA, post-excision. Furthermore, the system can also create transcriptional fusions with either ß-galactosidase or ß-glucuronidase as reporters, and exploits a variety of drug resistance markers so that multiple selectable fusions can be generated in a single strain. This system of various transposons has wide utility and can be combined in many different ways.

Effects of secondary metabolite extract from Phomopsis occulta on ß-amyloid aggregation.

Inhibition of ß-amyloid (Aß) aggregation is an attractive therapeutic and preventive strategy for the discovery of disease-modifying agents in Alzheimer's disease (AD). Phomopsis occulta is a new, salt-tolerant fungus isolated from mangrove Pongamia pinnata (L.) Pierre. We report here the inhibitory effects of secondary metabolites from Ph. occulta on the aggregation of Aß42. It was found that mycelia extracts (MEs) from Ph. occulta cultured with 0, 2, and 3 M NaCl exhibited inhibitory activity in an E. coli model of Aß aggregation. A water-soluble fraction, ME0-W-F1, composed of mainly small peptides, was able to reduce aggregation of an Aß42-EGFP fusion protein and an early onset familial mutation Aß42E22G-mCherry fusion protein in transfected HEK293 cells. ME0-W-F1 also antagonized the cytotoxicity of Aß42 in the neural cell line SH-SY5Y in dose-dependent manner. Moreover, SDS-PAGE and FT-IR analysis confirmed an inhibitory effect of ME0-W-F1 on the aggregation of Aß42 in vitro. ME0-W-F1 blocked the conformational transition of Aß42 from α-helix/random coil to ß-sheet, and thereby inhibited formation of Aß42 tetramers and high molecular weight oligomers. ME0-W-F1 and other water-soluble secondary metabolites from Ph. occulta therefore represent new candidate natural products against aggregation of Aß42, and illustrate the potential of salt tolerant fungi from mangrove as resources for the treatment of AD and other diseases.

Draft Genome Sequence of Serratia sp. Strain ATCC 39006, a Model Bacterium for Analysis of the Biosynthesis and Regulation of Prodigiosin, a Carbapenem, and Gas Vesicles.

Serratia sp. strain ATCC 39006 is a Gram-negative bacterium and a member of the Enterobacteriaceae that produces various bioactive secondary metabolites, including the tripyrrole red pigment prodigiosin and the ß-lactam antibiotic 1-carbapenen-2-em-3-carboxylic acid (a carbapenem). This strain is the only member of the Enterobacteriaceae known to naturally produce gas vesicles, as flotation organelles. Here we present the genome sequence of this strain, which has served as a model for analysis of the biosynthesis and regulation of antibiotic production.

Virulence and prodigiosin antibiotic biosynthesis in Serratia are regulated pleiotropically by the GGDEF/EAL domain protein, PigX.

Gram-negative bacteria of the genus Serratia are opportunistic human, plant, and insect pathogens. Serratia sp. strain ATCC 39006 secretes pectinases and cellulases and produces the secondary metabolites carbapenem and prodigiosin. Mutation of a gene (pigX) resulted in an extremely pleiotropic phenotype: prodigiosin antibiotic biosynthesis, plant virulence, and pectinase production were all elevated. PigX controlled secondary metabolism by repressing the transcription of the target prodigiosin biosynthetic operon (pigA-pigO). The transcriptional start site of pigX was determined, and pigX expression occurred in parallel with Pig production. Detailed quantitative intracellular proteome analyses enabled the identification of numerous downstream targets of PigX, including OpgG, mutation of which reduced the production of the plant cell wall-degrading enzymes and virulence. The highly pleiotropic PigX regulator contains GGDEF and EAL domains with noncanonical motifs and is predicted to be membrane associated. Genetic evidence suggests that PigX might function as a cyclic dimeric GMP phosphodiesterase. This is the first characterization of a GGDEF and EAL domain protein in Serratia and the first example of the regulation of antibiotic production by a GGDEF/EAL domain protein.

Anticancer and immunosuppressive properties of bacterial prodiginines.

Bacterial prodiginines are a family of red-pigmented, tripyrrolic compounds that display numerous biological activities, including antibacterial, antifungal, antiprotozoal, antimalarial, immunosuppressive and anticancer properties. Recently, significant progress has been made in understanding the biosynthesis and regulation of bacterial prodiginines. An understanding of the biosynthesis of prodiginines will allow engineering of bacterial strains capable of synthesizing novel prodiginines through rational design and mutasynthesis experiments. Bacterial prodiginines and synthetic derivatives are effective proapoptotic agents with multiple cellular targets, and they are active against numerous cancer cell lines, including multidrug-resistant cells, with little or no toxicity towards normal cell lines. A synthetic derivative, GX15-070 (Obatoclax), developed through structure-activity relationship studies of the pyrrolic ring A of GX15, is in multiple Phase I and II clinical trials in both single and dual-agent studies to treat different types of cancer. Therefore, prodiginines have real therapeutic potential in the clinic.

The biosynthesis and regulation of bacterial prodiginines.

The red-pigmented prodiginines are bioactive secondary metabolites produced by both Gram-negative and Gram-positive bacteria. Recently, these tripyrrole molecules have received renewed attention owing to reported immunosuppressive and anticancer properties. The enzymes involved in the biosynthetic pathways for the production of two of these molecules, prodigiosin and undecylprodigiosin, are now known. However, the biochemistry of some of the reactions is still poorly understood. The physiology and regulation of prodiginine production in Serratia and Streptomyces are now well understood, although the biological role of these pigments in the producer organisms remains unclear. However, research into the biology of pigment production will stimulate interest in the bioengineering of strains to synthesize useful prodiginine derivatives.