Polyketide synthases (PKSs) are crucial multidomain enzymes in diverse natural product biosynthesis. Parrots use a type I PKS to produce a unique pigment called psittacofulvin in their feathers. In domesticated budgerigars and lovebirds, the same amino acid substitution (R644W) within malonyl/acetyltransferase (MAT) domain of this enzyme has been shown to cause the blue phenotype with no psittacofulvin pigmentation, proposing a strong evolutionary constraint on the mechanism. Here, we identified seven previously unreported variants in PKS associated with defective psittacofulvin production in four diverse species, including three nonsense mutations. Intriguingly, three of the remaining nonsynonymous substitutions reside within the ketoacyl synthase (KS) domain, whereas one at MAT domain. The heterologous expression of these PKS variants in yeast confirmed complete or partial loss of psittacofulvin production. These findings establish PKS as a functionally conserved key-enzyme determining psittacofulvin-based hues among diverse parrots, highlighting multiple conserved domains essential for the PKS function.

• MeSH
• Pigments, Biological * biosynthesis   MeSH
• Mutation * MeSH
• Parrots * genetics   metabolism   MeSH
• Feathers metabolism   MeSH
• Pigmentation genetics   MeSH
• Polyketide Synthases * genetics   metabolism   MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Pigments, Biological * MeSH
• Polyketide Synthases * MeSH

The catastrophic loss of aquatic life in the Central European Oder River in 2022, caused by a toxic bloom of the haptophyte microalga Prymnesium parvum (in a wide sense, s.l.), underscores the need to improve our understanding of the genomic basis of the toxin. Previous morphological, phylogenetic, and genomic studies have revealed cryptic diversity within P. parvum s.l. and uncovered three clade-specific (types A, B, and C) prymnesin toxins. Here, we used state-of-the-art long-read sequencing and assembled the first haplotype-resolved diploid genome of a P. parvum type B from the strain responsible for the Oder disaster. Comparative analyses with type A genomes uncovered a genome-size expansion driven by repetitive elements in type B. We also found conserved synteny but divergent evolution in several polyketide synthase (PKS) genes, which are known to underlie toxin production in combination with environmental cues. We identified an approximately 20-kbp deletion in the largest PKS gene of type B that we link to differences in the chemical structure of types A and B prymnesins. Flow cytometry and electron microscopy analyses confirmed diploidy in the Oder River strain and revealed differences to closely related strains in both ploidy and morphology. Our results provide unprecedented resolution of strain diversity in P. parvum s.l. and a better understanding of the genomic basis of toxin variability in haptophytes. The reference-quality genome will enable us to better understand changes in microbial diversity in the face of increasing environmental pressures and provides a basis for strain-level monitoring of invasive Prymnesium in the future.

• Keywords
• genomics, golden alga, haptophyte, harmful algal bloom, ploidy, polyketide synthase, prymnesin,
• MeSH
• Phylogeny MeSH
• Haplotypes MeSH
• Haptophyta * genetics   MeSH
• Microalgae genetics   MeSH
• Marine Toxins genetics   MeSH
• Polyketide Synthases genetics   metabolism   MeSH
• Fishes genetics   MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Marine Toxins MeSH
• Polyketide Synthases MeSH

Cyanobacteria require iron for growth and often inhabit iron-limited habitats, yet only a few siderophores are known to be produced by them. We report that cyanobacterial genomes frequently encode polyketide synthase (PKS)/nonribosomal peptide synthetase (NRPS) biosynthetic pathways for synthesis of lipopeptides featuring β-hydroxyaspartate (β-OH-Asp), a residue known to be involved in iron chelation. Iron starvation triggered the synthesis of β-OH-Asp lipopeptides in the cyanobacteria Rivularia sp. strain PCC 7116, Leptolyngbya sp. strain NIES-3755, and Rubidibacter lacunae strain KORDI 51-2. The induced compounds were confirmed to bind iron by mass spectrometry (MS) and were capable of Fe3+ to Fe2+ photoreduction, accompanied by their cleavage, when exposed to sunlight. The siderophore from Rivularia, named cyanochelin A, was structurally characterized by MS and nuclear magnetic resonance (NMR) and found to contain a hydrophobic tail bound to phenolate and oxazole moieties followed by five amino acids, including two modified aspartate residues for iron chelation. Phylogenomic analysis revealed 26 additional cyanochelin-like gene clusters across a broad range of cyanobacterial lineages. Our data suggest that cyanochelins and related compounds are widespread β-OH-Asp-featuring cyanobacterial siderophores produced by phylogenetically distant species upon iron starvation. Production of photolabile siderophores by phototrophic cyanobacteria raises questions about whether the compounds facilitate iron monopolization by the producer or, rather, provide Fe2+ for the whole microbial community via photoreduction. IMPORTANCE All living organisms depend on iron as an essential cofactor for indispensable enzymes. However, the sources of bioavailable iron are often limited. To face this problem, microorganisms synthesize low-molecular-weight metabolites capable of iron scavenging, i.e., the siderophores. Although cyanobacteria inhabit the majority of the Earth's ecosystems, their repertoire of known siderophores is remarkably poor. Their genomes are known to harbor a rich variety of gene clusters with unknown function. Here, we report the awakening of a widely distributed class of silent gene clusters by iron starvation to yield cyanochelins, β-hydroxy aspartate lipopeptides involved in iron acquisition. Our results expand the limited arsenal of known cyanobacterial siderophores and propose products with ecological function for a number of previously orphan gene clusters.

• Keywords
• cyanobacteria, iron acquisition, lipopeptides, secondary metabolism, siderophores,
• MeSH
• Bacterial Proteins genetics   metabolism   MeSH
• Biosynthetic Pathways MeSH
• Phylogeny MeSH
• Lipopeptides metabolism   MeSH
• Multigene Family * MeSH
• Peptide Synthases genetics   metabolism   MeSH
• Polyketide Synthases genetics   metabolism   MeSH
• Siderophores biosynthesis   MeSH
• Cyanobacteria classification   enzymology   genetics   metabolism   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Bacterial Proteins MeSH
• Lipopeptides MeSH
• non-ribosomal peptide synthase MeSH Browser
• Peptide Synthases MeSH
• Polyketide Synthases MeSH
• Siderophores MeSH

Anatoxin-a, homoanatoxin-a, and dihydroanatoxin-a are potent cyanobacterial neurotoxins. They are biosynthesized in cyanobacteria from proline and acetate by a pathway involving three polyketide synthases. We report the identification of carboxy-anatoxin-a, carboxy-homoanatoxin-a, and carboxy-dihydroanatoxin-a in acidic extracts of Cuspidothrix issatschenkoi CHARLIE-1, Oscillatoria sp. PCC 6506, and Cylindrospermum stagnale PCC 7417, respectively, using liquid chromatography coupled to mass spectrometry. The structure of these carboxy derivatives was confirmed by mass spectrometry and by isotopic incorporation experiments using labeled proline and acetate. Each of these three cyanobacteria only produce one carboxy-anatoxin, suggesting that these metabolites are the product of the hydrolysis by AnaA, the type II thioesterase, of the thioesters bound to AnaG, the last polyketide synthase of the pathway. By measuring the rate of isotopic incorporation of labeled proline into carboxy-homoanatoxin-a and homoanatoxin-a produced by Oscillatoria sp. PCC 6506, we show that carboxy-homoanatoxin-a is the intracellular precursor of homoanatoxin-a, and that homoanatoxin-a is then excreted into the extracellular medium. The transformation of carboxy-homoanatoxin-a into homoanatoxin-a is a very slow two-step process, with accumulation of carboxy-homoanatoxin-a, suggesting that the decarboxylation is spontaneous and not enzymatically catalyzed. However, an unidentified and extracellular catalyst accelerates the decarboxylation when the cell extracts are prepared at neutral pH.

• MeSH
• Bacterial Toxins chemistry   metabolism   MeSH
• Bridged Bicyclo Compounds, Heterocyclic chemistry   metabolism   MeSH
• Chromatography, Liquid MeSH
• Molecular Structure MeSH
• Oscillatoria chemistry   MeSH
• Polyketide Synthases chemistry   metabolism   MeSH
• Proline chemistry   MeSH
• Cyanobacteria chemistry   metabolism   MeSH
• Cyanobacteria Toxins MeSH
• Tropanes chemistry   metabolism   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• anatoxin a MeSH Browser
• Bacterial Toxins MeSH
• Bridged Bicyclo Compounds, Heterocyclic MeSH
• homoanatoxin-a MeSH Browser
• Polyketide Synthases MeSH
• Proline MeSH
• Cyanobacteria Toxins MeSH
• Tropanes MeSH

The most diverse and versatile endophytic actinobacteria are relatively unexplored potential sources of bioactive metabolites useful for different medical, agricultural, and other commercial applications. Their diversity in symbiotic association with traditionally utilized medicinal plants of northeast India is scantly available. The present investigation assessed the genetic diversity of endophytic actinobacteria (n = 120) distributed around the root, stem, and leaf tissues of six selected medicinal plants (Emblica officinalis, Terminalia chebula, T. arjuna, Murraya koenigii, Rauwolfia serpentina, and Azadirachta indica) from three different protected areas of evergreen forest-the Gibbon Wildlife Sanctuary (GWS), the Kaziranga National Park (KNP), and the North East Ecological Park (NEEP) of Assam, India. The samples were collected in two seasons (summer and winter). The overall phylogenetic analysis showed significant genetic diversity with 18 distinct genera belonging to 12 families. Overall, the occurrence of Streptomyces genus was predominant across all three sampling sites (76.66%), in both the sampling season (summer and winter). Shannon's and Simpson's diversity estimates showed their presence at A. indica (1.496, 0.778), R. serpentina (1.470, 0.858), and E. officinalis (0.975, 0.353). Among the site sampled, GWS had the most diverse community of actinobacteria (Shannon = 0.86 and Simpson = 0.557). The isolates were antagonistically more active against the investigated plant pathogenic bacteria than fungal pathogens. Further analysis revealed the prevalence of polyketide synthase genes (PKS) type II (84%) and PKS type I (16%) in the genome of the antimicrobial isolates. The overall findings confirmed the presence of biosynthetically active diverse actinobacterial members in the selected medicinal plants which offer potential opportunities towards the exploration of biologically active compounds.

• MeSH
• Actinobacteria classification   genetics   isolation & purification   physiology   MeSH
• Antibiosis * MeSH
• Bacteria MeSH
• Bacterial Proteins genetics   metabolism   MeSH
• Endophytes classification   genetics   isolation & purification   physiology   MeSH
• Phylogeny * MeSH
• Bacterial Physiological Phenomena MeSH
• Fungi physiology   MeSH
• Plants, Medicinal microbiology   MeSH
• Polyketide Synthases genetics   metabolism   MeSH
• Seasons MeSH
• Symbiosis MeSH
• Publication type
• Journal Article MeSH
• Geographicals
• India MeSH
• Names of Substances
• Bacterial Proteins MeSH
• Polyketide Synthases MeSH

In this work, the binding mechanism of new Polyketide Synthase 13 (Pks13) inhibitors has been studied through molecular dynamics simulation and free energy calculations. The drug Tam1 and its analogs, belonging to the benzofuran class, were submitted to 100 ns simulations, and according to the results obtained for root mean square deviation, all the simulations converged from approximately 30 ns. For the analysis of backbone flotation, the root mean square fluctuations were plotted for the Cα atoms; analysis revealed that the greatest fluctuation occurred in the residues that are part of the protein lid domain. The binding free energy value (ΔGbind) obtained for the Tam16 lead molecule was of -51.43 kcal/mol. When comparing this result with the ΔGbind values for the remaining analogs, the drug Tam16 was found to be the highest ranked: this result is in agreement with the experimental results obtained by Aggarwal and collaborators, where it was verified that the IC50 for Tam16 is the smallest necessary to inhibit the Pks13 (IC50 = 0.19 μM). The energy decomposition analysis suggested that the residues which most interact with inhibitors are: Ser1636, Tyr1637, Asn1640, Ala1667, Phe1670, and Tyr1674, from which the greatest energy contribution to Phe1670 was particularly notable. For the lead molecule Tam16, a hydrogen bond with the hydroxyl of the phenol not observed in the other analogs induced a more stable molecular structure. Aggarwal and colleagues reported this hydrogen bonding as being responsible for the stability of the molecule, optimizing its physic-chemical, toxicological, and pharmacokinetic properties.

• Keywords
• CNPq, National Council for Scientific and Technological Development, CoA, coenzyme A, FAS, fatty acid synthase, GAFF, general amber force field, GB, generalized born, HB, hydrogen bonds, INH, isoniazid, KatG, catalase-peroxidase, MD, molecular dynamics, MDR, multi-drug resistant, MM/GBSA, molecular mechanics/generalized-born surface area, NAD, nicotinamide adenine dinucleotide, NS, nanoseconds, PCA, acyl carrier protein, Pks13, Pks13, polyketide synthase 13, RESP, restrained electrostatic potential, RMSD, root mean square deviation, RMSF, root mean square fluctuations, TB, tuberculosis, TE, C-terminal thioesterase, XDR, extensively drug resistant, benzofuran, free energy, inhibitors, molecular dynamics, Δ internal energy, Δ, Van Der Waals contributions, Δ, electrostatic contribution, Δ, electrostatic contributions, Δ, energy of desolvation, Δ, energy of the molecular mechanics, Δ, non-polar contributions, Δ, polar contributions, Δ, polar solvation contribution,
• MeSH
• Amino Acids MeSH
• Antitubercular Agents chemistry   pharmacology   MeSH
• Bacterial Proteins antagonists & inhibitors   chemistry   MeSH
• Benzofurans chemistry   pharmacology   MeSH
• Protein Conformation MeSH
• Molecular Structure MeSH
• Drug Discovery MeSH
• Polyketide Synthases antagonists & inhibitors   chemistry   MeSH
• Molecular Dynamics Simulation * MeSH
• Molecular Docking Simulation * MeSH
• Protein Binding MeSH
• Binding Sites MeSH
• Hydrogen Bonding MeSH
• Structure-Activity Relationship MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Amino Acids MeSH
• Antitubercular Agents MeSH
• Bacterial Proteins MeSH
• benzofuran MeSH Browser
• Benzofurans MeSH
• polyketide synthase Pks13, Mycobacterium tuberculosis MeSH Browser
• Polyketide Synthases MeSH

Puwainaphycins (PUWs) and minutissamides (MINs) are structurally analogous cyclic lipopeptides possessing cytotoxic activity. Both types of compound exhibit high structural variability, particularly in the fatty acid (FA) moiety. Although a biosynthetic gene cluster responsible for synthesis of several PUW variants has been proposed in a cyanobacterial strain, the genetic background for MINs remains unexplored. Herein, we report PUW/MIN biosynthetic gene clusters and structural variants from six cyanobacterial strains. Comparison of biosynthetic gene clusters indicates a common origin of the PUW/MIN hybrid nonribosomal peptide synthetase and polyketide synthase. Surprisingly, the biosynthetic gene clusters encode two alternative biosynthetic starter modules, and analysis of structural variants suggests that initiation by each of the starter modules results in lipopeptides of differing lengths and FA substitutions. Among additional modifications of the FA chain, chlorination of minutissamide D was explained by the presence of a putative halogenase gene in the PUW/MIN gene cluster of Anabaena minutissima strain UTEX B 1613. We detected PUW variants bearing an acetyl substitution in Symplocastrum muelleri strain NIVA-CYA 644, consistent with an O-acetyltransferase gene in its biosynthetic gene cluster. The major lipopeptide variants did not exhibit any significant antibacterial activity, and only the PUW F variant was moderately active against yeast, consistent with previously published data suggesting that PUWs/MINs interact preferentially with eukaryotic plasma membranes.IMPORTANCE Herein, we deciphered the most important biosynthetic traits of a prominent group of bioactive lipopeptides. We reveal evidence for initiation of biosynthesis by two alternative starter units hardwired directly in the same gene cluster, eventually resulting in the production of a remarkable range of lipopeptide variants. We identified several unusual tailoring genes potentially involved in modifying the fatty acid chain. Careful characterization of these biosynthetic gene clusters and their diverse products could provide important insight into lipopeptide biosynthesis in prokaryotes. Some of the variants identified exhibit cytotoxic and antifungal properties, and some are associated with a toxigenic biofilm-forming strain. The findings may prove valuable to researchers in the fields of natural product discovery and toxicology.

• Keywords
• biosynthesis, cyanobacteria, fatty acyl-AMP ligase, lipopeptides, nonribosomal peptide synthetase,
• MeSH
• Anabaena genetics   MeSH
• Antifungal Agents MeSH
• Anti-Infective Agents MeSH
• Genes, Bacterial genetics   MeSH
• Bacterial Proteins genetics   MeSH
• Peptides, Cyclic biosynthesis   chemistry   genetics   MeSH
• Lipopeptides biosynthesis   chemistry   genetics   pharmacology   MeSH
• Multigene Family MeSH
• Peptide Synthases genetics   MeSH
• Polyketide Synthases genetics   MeSH
• Cyanobacteria genetics   metabolism   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Antifungal Agents MeSH
• Anti-Infective Agents MeSH
• Bacterial Proteins MeSH
• Peptides, Cyclic MeSH
• Lipopeptides MeSH
• non-ribosomal peptide synthase MeSH Browser
• Peptide Synthases MeSH
• Polyketide Synthases MeSH

The pederin family includes a number of bioactive compounds isolated from symbiotic organisms of diverse evolutionary origin. Pederin is linked to beetle-induced dermatitis in humans, and pederin family members possess potent antitumor activity caused by selective inhibition of the eukaryotic ribosome. Their biosynthesis is accomplished by a polyketide/nonribosomal peptide synthetase machinery employing an unusual trans-acyltransferase mechanism. Here, we report a novel pederin type compound, cusperin, from the free-living cyanobacterium Cuspidothrix issatschenkoi (earlier Aphanizomenon). The chemical structure of cusperin is similar to that of nosperin recently isolated from the lichen cyanobiont Nostoc sharing the tehrahydropyran moiety and major part of the linear backbone. However, the cusperin molecule is extended by a glycine residue and lacks one hydroxyl substituent. Pederins were previously thought to be exclusive to symbiotic relationships. However, C. issatschenkoi is a nonsymbiotic planktonic organism and a frequent component of toxic water blooms. Cusperin is devoid of the cytotoxic activity reported for other pederin family members. Hence, our findings raise questions about the role of pederin analogues in cyanobacteria and broaden the knowledge of ecological distribution of this group of polyketides.

• MeSH
• Genes, Bacterial MeSH
• Spectrometry, Mass, Electrospray Ionization MeSH
• Magnetic Resonance Spectroscopy MeSH
• Multigene Family MeSH
• Peptide Synthases metabolism   MeSH
• Polyketide Synthases metabolism   MeSH
• Polyketides isolation & purification   metabolism   MeSH
• Cyanobacteria genetics   metabolism   MeSH
• Symbiosis MeSH
• Tandem Mass Spectrometry MeSH
• Publication type
• Letter MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• non-ribosomal peptide synthase MeSH Browser
• Peptide Synthases MeSH
• Polyketide Synthases MeSH
• Polyketides MeSH

Cyanobacterial lipopeptides have antimicrobial and antifungal bioactivities with potential for use in pharmaceutical research. However, due to their hemolytic activity and cytotoxic effects on human cells, they may pose a health issue if produced in substantial amounts in the environment. In bacteria, lipopeptides can be synthesized via several well-evidenced mechanisms. In one of them, fatty acyl-AMP ligase (FAAL) initiates biosynthesis by activation of a fatty acyl residue. We have performed a bioinformatic survey of the cyanobacterial genomic information available in the public databases for the presence of FAAL-containing non-ribosomal peptide synthetase/polyketide synthetase (NRPS/PKS) biosynthetic clusters, as a genetic basis for lipopeptide biosynthesis. We have identified 79 FAAL genes associated with various NRPS/PKS clusters in 16% of 376 cyanobacterial genomic assemblies available, suggesting that FAAL is frequently incorporated in NRPS/PKS biosynthetases. FAAL was present either as a stand-alone protein or fused either to NRPS or PKS. Such clusters were more frequent in derived phylogenetic lineages with larger genome sizes, which is consistent with the general pattern of NRPS/PKS pathways distribution. The putative lipopeptide clusters were more frequently found in genomes of cyanobacteria that live attached to surfaces and are capable of forming microbial biofilms. While lipopeptides are known in other bacterial groups to play a role in biofilm formation, motility, and colony expansion, their functions in cyanobacterial biofilms need to be tested experimentally. According to our data, benthic and terrestrial cyanobacteria should be the focus of a search for novel candidates for lipopeptide drug synthesis and the monitoring of toxic lipopeptide production.

• Keywords
• cyanobacteria, fatty-acyl AMP ligase, genome mining, lipopeptides, microbial biofilm, non-ribosomal peptide synthesis,
• MeSH
• Bacterial Proteins genetics   MeSH
• Genome, Bacterial * MeSH
• Peptide Synthases genetics   MeSH
• Polyketide Synthases genetics   MeSH
• Cyanobacteria genetics   MeSH
• Computational Biology MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Bacterial Proteins MeSH
• non-ribosomal peptide synthase MeSH Browser
• Peptide Synthases MeSH
• Polyketide Synthases MeSH

A putative operon encoding the biosynthetic pathway for the cytotoxic cyanobacterial lipopeptides puwainphycins was identified in Cylindrospermum alatosporum. Bioinformatics analysis enabled sequential prediction of puwainaphycin biosynthesis; this process is initiated by the activation of a fatty acid residue via fatty acyl-AMP ligase and continued by a multidomain non-ribosomal peptide synthetase/polyketide synthetase. High-resolution mass spectrometry and nuclear magnetic resonance spectroscopy measurements proved the production of puwainaphycin F/G congeners differing in FA chain length formed by either 3-amino-2-hydroxy-4-methyl dodecanoic acid (4-methyl-Ahdoa) or 3-amino-2-hydroxy-4-methyl tetradecanoic acid (4-methyl-Ahtea). Because only one puwainaphycin operon was recovered in the genome, we suggest that the fatty acyl-AMP ligase and one of the amino acid adenylation domains (Asn/Gln) show extended substrate specificity. Our results provide the first insight into the biosynthesis of frequently occurring β-amino fatty acid lipopeptides in cyanobacteria, which may facilitate analytical assessment and development of monitoring tools for cytotoxic cyanobacterial lipopeptides.

• MeSH
• Molecular Sequence Annotation MeSH
• Genes, Bacterial MeSH
• Bacterial Proteins genetics   physiology   MeSH
• Biosynthetic Pathways MeSH
• Ligases genetics   physiology   MeSH
• Lipopeptides biosynthesis   MeSH
• Molecular Sequence Data MeSH
• Multigene Family MeSH
• Polyketide Synthases genetics   physiology   MeSH
• Cyanobacteria enzymology   genetics   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Bacterial Proteins MeSH
• Ligases MeSH
• Lipopeptides MeSH
• Polyketide Synthases MeSH
• puwainaphycin F MeSH Browser
• puwainaphycin G MeSH Browser