Pyonitrins A-D: Chimeric Natural Products Produced by Pseudomonas protegens

Iodide Enhances the Production of Pseurotin D over Pseurotin A by Inverting the Preference for the SN2 versus the SN2' Product in the Final Nonenzymatic Step

Nonenzymatic reactions, though critical in natural product biosynthesis, are significantly challenging to control. Adding 3% NaI to the culture medium of Penicillium janczewskii significantly increased pseurotin D (1) production and decreased pseurotin A (2) production. Previously, 1 and 2 were suggested to be produced via a nonenzymatic reaction, where the epoxide at C-10 undergoes SN2 (2) or SN2' (1) reactions. We confirmed that 1 was isolated as a 1:1 mixture of C-13 epimers by spectral elucidation via CP3 analysis aided by selective excitation NMR methods, which supported that 1 was produced through a nonenzymatic SN2' reaction. We propose that NaI increased the ratio of 1 by causing steric hindrance at the C-11 position of the transient intermediate, which makes C-13 more preferred in the SN2/SN2' competition.

Discovery of a Chimeric Polyketide Family as Cancer Immunogenic Chemotherapeutic Leads

Discovery of cancer immunogenic chemotherapeutics represents an emerging, highly promising direction for cancer treatment that uses a chemical drug to achieve the efficacy of both chemotherapy and immunotherapy. Herein, we report a high-throughput screening platform and the subsequent discovery of a new class of cancer immunogenic chemotherapeutic leads. Our platform integrates informatics-based activity metabolomics for the rapid identification of microbial natural products with both novel structures and potent activities. Additionally, we demonstrate the use of microcrystal electron diffraction (MicroED) for direct structure elucidation of lead compounds from partially purified mixtures. Using this strategy to screen geographically and phylogenetically diverse microbial metabolites against pseudomyxoma peritonei, a rare and severe cancer, we discovered a new class of leads, aspercyclicins. The aspercyclicins feature an unprecedented tightly packed polycyclic polyketide scaffold that comprises continuous fused, bridged, and spiro rings. The biogenesis of aspercyclicins involves two distinct biosynthetic pathways, leading to formation of chimeric compounds that cannot be predicted by bottom-up approaches mining natural product biosynthetic genes. With comparable potency to some clinically used anticancer drugs, aspercyclicins are active against multiple cancer cell types by inducing immunogenic cell death (ICD), including the release of damage-associated molecular patterns and subsequent phagocytosis of cancer cells. The broad-spectrum ICD-inducing activity of aspercyclicins, combined with their low toxicity to normal cells, represents a new class of potential cancer immunogenic chemotherapeutics and, particularly, the first drug lead for pseudomyxoma peritonei treatment.

Scaling up for success: from bioactive natural products to new medicines

Covering 1986 to presentNatural product drug discovery at Novartis has a long and successful history of delivering life saving medicines to millions of patients. In this viewpoint, we are presenting the tools we use and challenges we face as we advance natural products from early research into development and beyond. We are leveraging our collection of 90 000 microbial strains and 20 000 isolated natural products to find new medications in an interdisciplinary approach that requires expertise in microbiology, computational biology, synthetic biology, chemistry, and process development. Technological advances, particularly in genome engineering and data science have transformed our field, accelerating discovery and facilitating sustainable compound supply. Emerging new modalities such as antibody drug conjugates, radioligand therapies and xRNA-based medications offer new opportunities for natural product-derived drugs. By taking advantage of these new modalities and the most recent research technologies, natural products will significantly contribute to the medicines of the future.

Discovery of A Chimeric Polyketide Family as Cancer Immunogenic Chemotherapeutic Leads

Discovery of cancer immunogenic chemotherapeutics represents an emerging, highly promising direction for cancer treatment that uses a chemical drug to achieve the efficacy of both chemotherapy and immunotherapy. Herein we report a high-throughput screening platform and the subsequent discovery of a new class of cancer immunogenic chemotherapeutic leads. Our platform integrates informatics-based activity metabolomics for rapid identification of microbial natural products with both novel structures and potent activities. Additionally, we demonstrate the use of microcrystal electron diffraction (MicroED) for direct structure elucidation of the lead compounds from partially purified mixtures. Using this strategy to screen geographically and phylogenetically diverse microbial metabolites against pseudomyxoma peritonei, a rare and severe cancer, we discovered a new class of leads, aspercyclicins. The aspercyclicins feature an unprecedented tightly packed polycyclic polyketide scaffold that comprises continuous fused, bridged, and spiro rings. The biogenesis of aspercyclicins involves two distinct biosynthetic pathways, leading to formation of chimeric compounds that cannot be predicted by bottom-up approaches mining natural products biosynthetic genes. With comparable potency to some clinically used anticancer drugs, aspercyclicins are active against multiple cancer cell types by inducing immunogenic cell death (ICD), including the release of damage-associated molecular patterns and subsequent phagocytosis of cancer cells. The broad-spectrum ICD-inducing activity of aspercyclicins, combined with their low toxicity to normal cells, represents a new class of potential cancer immunogenic chemotherapeutics and particularly the first drug lead for pseudomyxoma peritonei treatment.

Metal chelation as an antibacterial strategy for Pseudomonas aeruginosa and Acinetobacter baumannii

It is estimated that by 2050, bacterial infections will cause 1.8 million more deaths than cancer annually, and the current lack of antibiotic drug discovery is only exacerbating the crisis. Two pathogens in particular, Gram-negative bacteria A. baumannii and P. aeruginosa, are of grave concern because of their heightened multi-drug resistance due to a dense, impermeable outer membrane. However, targeting specific cellular processes may prove successful in overcoming bacterial resistance. This review will concentrate on a novel approach to combatting pathogenicity by disarming bacteria through the disruption of metal homeostasis to reduce virulence and enhance antibiotic uptake. The varying levels of success in bringing metallophores to clinical trials, with currently only one FDA-approved siderophore antibiotic to date, will also be detailed.

Siderophores: A Case Study in Translational Chemical Biology

Siderophores are metal-binding secondary metabolites that assist in iron homeostasis and have been of interest to the scientific community for the last half century. Foundational siderophore research has enabled several translational applications including siderophore-antibiotic and siderophore-peptide conjugates, identification of new antimicrobial targets, advances in disease imaging, and novel therapeutics. This review aims to connect the basic science research (biosynthesis, cellular uptake, gene regulation, and effects on homeostasis) of well-known siderophores with the successive translational application that results. Intertwined throughout are connections to the career of Christopher T. Walsh, his impact on the field of chemical biology, and the legacy of his trainees who continue to innovate.

Structurally Diverse Macrolactams from an Antarctic Streptomyces Species

Twelve new polyenic macrolactams, cyclamenols G-R (1 and 3-13), together with the known analogue cyclamenol A (2), were isolated from Streptomyces sp. OUCMDZ-4348. Their structures were elucidated by spectroscopic analysis, quantum chemical calculations, chemical derivatizations, and Mosher's methods. The sequenced genome of OUCMDZ-4348 revealed the putative biosynthetic gene cluster of cyclamenols. It was proposed that the polycyclic natural products, cyclamenols H-R, might be formed from cyclamenols A and G through nonenzymatic intramolecular cycloadditions and oxidative cyclizations.

Anithiactin D, a Phenylthiazole Natural Product from Mudflat-Derived Streptomyces sp., Suppresses Motility of Cancer Cells

Anithiactin D (1), a 2-phenylthiazole class of natural products, was isolated from marine mudflat-derived actinomycetes Streptomyces sp. 10A085. The chemical structure of 1 was elucidated based on the interpretation of NMR and MS data. The absolute configuration of 1 was determined by comparing the experimental and calculated electronic circular dichroism (ECD) spectral data. Anithiactin D (1) significantly decreased cancer cell migration and invasion activities at a concentration of 5 μM via downregulation of the epithelial-to-mesenchymal transition (EMT) markers in A549, AGS, and Caco-2 cell lines. Moreover, 1 inhibited the activity of Rho GTPases, including Rac1 and RhoA in the A549 cell line, suppressed RhoA in AGS and Caco-2 cell lines, and decreased the mRNA expression levels of some matrix metalloproteinases (MMPs) in AGS and Caco-2 cell lines. Thus 1, which is a new entity of the 2-phenylthiazole class of natural products with a unique aniline-indole fused moiety, is a potent inhibitor of the motility of cancer cells.

Metabolomics and Genomics Enable the Discovery of a New Class of Nonribosomal Peptidic Metallophores from a Marine Micromonospora

Although microbial genomes harbor an abundance of biosynthetic gene clusters, there remain substantial technological gaps that impair the direct correlation of newly discovered gene clusters and their corresponding secondary metabolite products. As an example of one approach designed to minimize or bridge such gaps, we employed hierarchical clustering analysis and principal component analysis (hcapca, whose sole input is MS data) to prioritize 109 marine Micromonospora strains and ultimately identify novel strain WMMB482 as a candidate for in-depth "metabologenomics" analysis following its prioritization. Highlighting the power of current MS-based technologies, not only did hcapca enable the discovery of one new, nonribosomal peptide bearing an incredible diversity of unique functional groups, but metabolomics for WMMB482 unveiled 16 additional congeners via the application of Global Natural Product Social molecular networking (GNPS), herein named ecteinamines A-Q (1-17). The ecteinamines possess an unprecedented skeleton housing a host of uncommon functionalities including a menaquinone pathway-derived 2-naphthoate moiety, 4-methyloxazoline, the first example of a naturally occurring Ψ[CH2NH] "reduced amide", a methylsulfinyl moiety, and a d-cysteinyl residue that appears to derive from a unique noncanonical epimerase domain. Extensive in silico analysis of the ecteinamine (ect) biosynthetic gene cluster and stable isotope-feeding experiments helped illuminate the novel enzymology driving ecteinamine assembly as well the role of cluster collaborations or "duets" in producing such structurally complex agents. Finally, ecteinamines were found to bind nickel, cobalt, zinc, and copper, suggesting a possible biological role as broad-spectrum metallophores.

Naturally Occurring Organohalogen Compounds-A Comprehensive Review

The present volume is the third in a trilogy that documents naturally occurring organohalogen compounds, bringing the total number-from fewer than 25 in 1968-to approximately 8000 compounds to date. Nearly all of these natural products contain chlorine or bromine, with a few containing iodine and, fewer still, fluorine. Produced by ubiquitous marine (algae, sponges, corals, bryozoa, nudibranchs, fungi, bacteria) and terrestrial organisms (plants, fungi, bacteria, insects, higher animals) and universal abiotic processes (volcanos, forest fires, geothermal events), organohalogens pervade the global ecosystem. Newly identified extraterrestrial sources are also documented. In addition to chemical structures, biological activity, biohalogenation, biodegradation, natural function, and future outlook are presented.

Metabologenomics analysis of Pseudomonas sp. So3.2b, an Antarctic strain with bioactivity against Rhizoctonia solani

Introduction

Phytopathogenic fungi are a considerable concern for agriculture, as they can threaten the productivity of several crops worldwide. Meanwhile, natural microbial products are acknowledged to play an important role in modern agriculture as they comprehend a safer alternative to synthetic pesticides. Bacterial strains from underexplored environments are a promising source of bioactive metabolites.

Methods

We applied the OSMAC (One Strain, Many Compounds) cultivation approach, in vitro bioassays, and metabolo-genomics analyses to investigate the biochemical potential of Pseudomonas sp. So3.2b, a strain isolated from Antarctica. Crude extracts from OSMAC were analyzed through HPLC-QTOF-MS/MS, molecular networking, and annotation. The antifungal potential of the extracts was confirmed against Rhizoctonia solani strains. Moreover, the whole-genome sequence was studied for biosynthetic gene clusters (BGCs) identification and phylogenetic comparison.

Results and Discussion

Molecular networking revealed that metabolite synthesis has growth media specificity, and it was reflected in bioassays results against R. solani. Bananamides, rhamnolipids, and butenolides-like molecules were annotated from the metabolome, and chemical novelty was also suggested by several unidentified compounds. Additionally, genome mining confirmed a wide variety of BGCs present in this strain, with low to no similarity with known molecules. An NRPS-encoding BGC was identified as responsible for producing the banamides-like molecules, while phylogenetic analysis demonstrated a close relationship with other rhizosphere bacteria. Therefore, by combining -omics approaches and in vitro bioassays, our study demonstrates that Pseudomonas sp. So3.2b has potential application to agriculture as a source of bioactive metabolites.

Navigating and expanding the roadmap of natural product genome mining tools

Natural products are structurally highly diverse and exhibit a wide array of biological activities. As a result, they serve as an important source of new drug leads. Traditionally, natural products have been discovered by bioactivity-guided fractionation. The advent of genome sequencing technology has resulted in the introduction of an alternative approach towards novel natural product scaffolds: Genome mining. Genome mining is an in-silico natural product discovery strategy in which sequenced genomes are analyzed for the potential of the associated organism to produce natural products. Seemingly universal biosynthetic principles have been deciphered for most natural product classes that are used to detect natural product biosynthetic gene clusters using pathway-encoded conserved key enzymes, domains, or motifs as bait. Several generations of highly sophisticated tools have been developed for the biosynthetic rule-based identification of natural product gene clusters. Apart from these hard-coded algorithms, multiple tools that use machine learning-based approaches have been designed to complement the existing genome mining tool set and focus on natural product gene clusters that lack genes with conserved signature sequences. In this perspective, we take a closer look at state-of-the-art genome mining tools that are based on either hard-coded rules or machine learning algorithms, with an emphasis on the confidence of their predictions and potential to identify non-canonical natural product biosynthetic gene clusters. We highlight the genome mining pipelines' current strengths and limitations by contrasting their advantages and disadvantages. Moreover, we introduce two indirect biosynthetic gene cluster identification strategies that complement current workflows. The combination of all genome mining approaches will pave the way towards a more comprehensive understanding of the full biosynthetic repertoire encoded in microbial genome sequences.

Ulleungdolin, a Polyketide-Peptide Hybrid Bearing a 2,4-Di-O-methyl-β-d-antiarose from Streptomyces sp. 13F051 Co-cultured with Leohumicola minima 15S071

A new secondary metabolite, ulleungdolin (1), was isolated from the co-culture of an actinomycete, Streptomyces sp. 13F051, and a fungus, Leohumicola minima 15S071. Based on the NMR, UV, and MS data, it was deduced that the planar structure of 1 comprised an isoindolinone (IsoID) with an octanoic acid, a tripeptide, and a sugar. The tripeptide has the unprecedented amino acids norcoronamic acid, 3-hydroxy-glutamine, and 4-hydroxy-phenylglycine and is linked by a C-N bond with IsoID. The absolute configurations were determined by chemical derivatization, extensive spectroscopic methods, and electronic circular dichroism calculations and supported by bioinformatic analyses. Bioactivity evaluation studies indicated that 1 had an antimigration effect on MDA-MB-231 breast cancer cells.

Biomimetic Total Synthesis and Investigation of the Non-Enzymatic Chemistry of Oxazinin A

We report the first total synthesis of an antimycobacterial natural product oxazinin A that takes advantage of a multi-component cascade reaction of anthranilic acid and a precursor polyketide containing an aldehyde. The route utilized for the synthesis of the pseudodimeric oxazinin A validates a previously proposed biosynthetic mechanism, invoking a non-enzymatic pathway to the complex molecule. We found a 76 : 10 : 9 : 5 ratio of oxazinin diastereomers from the synthetic cascade, which is an identical match to that found in the fermentation media from the fungus Eurotiomycetes 110162. Further investigation of the non-enzymatic formation of oxazinin A using 1 H-15 N HMBC NMR spectroscopy allowed for a plausible determination of the stepwise mechanism. The developed route is highly amenable for the synthesis of diverse sets of analogs around the oxazinin scaffold to study structure-activity relationships (SAR).

Chimeric natural products derived from medermycin and the nature-inspired construction of their polycyclic skeletons

Medermycin, produced by Streptomyces species, represents a family of antibiotics with significant activity against Gram-positive pathogens. The biosynthesis of this family of natural products has been studied, and new skeletons related to medermycin have rarely been reported until recently. Herein, we report eight chimeric medermycin-type natural products with unusual polycyclic skeletons. The formation of these compounds features some key nonenzymatic steps, which inspired us to construct complex polycyclic skeletons via three efficient one-step reactions under mild conditions. This strategy was further developed to efficiently synthesize analogues for biological activity studies. The synthetic compounds, chimedermycins L and M, and sekgranaticin B, show potent antibacterial activity against Staphylococcus aureus, methicillin-resistant Staphylococcus aureus, and methicillin-resistant Staphylococcus epidermidis. This work paves the way for understanding the nonenzymatic formation of complex natural products and using it to synthesize natural product derivatives.

Nonenzymatic Reactions in Natural Product Formation

Biosynthetic mechanisms of natural products primarily depend on systems of protein catalysts. However, within the field of biosynthesis, there are cases in which the inherent chemical reactivity of metabolic intermediates and substrates evades the involvement of enzymes. These reactions are difficult to characterize based on their reactivity and occlusion within the milieu of the cellular environment. As we continue to build a strong foundation for how microbes and higher organisms produce natural products, therein lies a need for understanding how protein independent or nonenzymatic biosynthetic steps can occur. We have classified such reactions into four categories: intramolecular, multicomponent, tailoring, and light-induced reactions. Intramolecular reactions is one of the most well studied in the context of biomimetic synthesis, consisting of cyclizations and cycloadditions due to the innate reactivity of the intermediates. There are two subclasses that make up multicomponent reactions, one being homologous multicomponent reactions which results in dimeric and pseudodimeric natural products, and the other being heterologous multicomponent reactions, where two or more precursors from independent biosynthetic pathways undergo a variety of reactions to produce the mature natural product. The third type of reaction discussed are tailoring reactions, where postmodifications occur on the natural products after the biosynthetic machinery is completed. The last category consists of light-induced reactions involving ecologically relevant UV light rather than high intensity UV irradiation that is traditionally used in synthetic chemistry. This review will cover recent nonenzymatic biosynthetic mechanisms and include sources for those reviewed previously.

Complex peptide natural products: Biosynthetic principles, challenges and opportunities for pathway engineering

Complex peptide natural products exhibit diverse biological functions and a wide range of physico-chemical properties. As a result, many peptides have entered the clinics for various applications. Two main routes for the biosynthesis of complex peptides have evolved in nature: ribosomally synthesized and post-translationally modified peptide (RiPP) biosynthetic pathways and non-ribosomal peptide synthetases (NRPSs). Insights into both bioorthogonal peptide biosynthetic strategies led to the establishment of universal principles for each of the two routes. These universal rules can be leveraged for the targeted identification of novel peptide biosynthetic blueprints in genome sequences and used for the rational engineering of biosynthetic pathways to produce non-natural peptides. In this review, we contrast the key principles of both biosynthetic routes and compare the different biochemical strategies to install the most frequently encountered peptide modifications. In addition, the influence of the fundamentally different biosynthetic principles on past, current and future engineering approaches is illustrated. Despite the different biosynthetic principles of both peptide biosynthetic routes, the arsenal of characterized peptide modifications encountered in RiPP and NRPS systems is largely overlapping. The continuous expansion of the biocatalytic toolbox of peptide modifying enzymes for both routes paves the way towards the production of complex tailor-made peptides and opens up the possibility to produce NRPS-derived peptides using the ribosomal route and vice versa.

Beyond Soil-Dwelling Actinobacteria: Fantastic Antibiotics and Where to Find Them

Bacterial secondary metabolites represent an invaluable source of bioactive molecules for the pharmaceutical and agrochemical industries. Although screening campaigns for the discovery of new compounds have traditionally been strongly biased towards the study of soil-dwelling Actinobacteria, the current antibiotic resistance and discovery crisis has brought a considerable amount of attention to the study of previously neglected bacterial sources of secondary metabolites. The development and application of new screening, sequencing, genetic manipulation, cultivation and bioinformatic techniques have revealed several other groups of bacteria as producers of striking chemical novelty. Biosynthetic machineries evolved from independent taxonomic origins and under completely different ecological requirements and selective pressures are responsible for these structural innovations. In this review, we summarize the most important discoveries related to secondary metabolites from alternative bacterial sources, trying to provide the reader with a broad perspective on how technical novelties have facilitated the access to the bacterial metabolic dark matter.

Bacillimidazoles A-F, Imidazolium-Containing Compounds Isolated from a Marine Bacillus

Chemical investigations of a marine sponge-associated Bacillus revealed six new imidazolium-containing compounds, bacillimidazoles A-F (1-6). Previous reports of related imidazolium-containing natural products are rare. Initially unveiled by timsTOF (trapped ion mobility spectrometry) MS data, extensive HRMS and 1D and 2D NMR analyses enabled the structural elucidation of 1-6. In addition, a plausible biosynthetic pathway to bacillimidazoles is proposed based on isotopic labeling experiments and invokes the highly reactive glycolytic adduct 2,3-butanedione. Combined, the results of structure elucidation efforts, isotopic labeling studies and bioinformatics suggest that 1-6 result from a fascinating intersection of primary and secondary metabolic pathways in Bacillus sp. WMMC1349. Antimicrobial assays revealed that, of 1-6, only compound six displayed discernible antibacterial activity, despite the close structural similarities shared by all six natural products.

Isolation, Whole-Genome Sequencing, and Annotation of Three Unclassified Antibiotic-Producing Bacteria, Enterobacter sp. Strain RIT 637, Pseudomonas sp. Strain RIT 778, and Deinococcus sp. Strain RIT 780

We report the isolation, whole-genome sequencing, and annotation of Enterobacter sp. strain RIT 637, Pseudomonas sp. strain RIT 778, and Deinococcus sp. strain RIT 780. Disk diffusion assays using spent medium demonstrated that all bacteria produced bactericidal compounds against Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, and Staphylococcus aureus ATCC 25923.

Pyochelin Biosynthetic Metabolites Bind Iron and Promote Growth in Pseudomonads Demonstrating Siderophore-like Activity

Pseudomonads employ several strategies to sequester iron vital for their survival including the use of siderophores such as pyoverdine and pyochelin. Similar in structure but significantly less studied are pyochelin biosynthetic byproducts, dihydroaeruginoic acid, aeruginoic acid, aeruginaldehyde (IQS), and aeruginol, along with two other structurally related molecules, aerugine and pyonitrins A-D, which have all been isolated from numerous Pseudomonad extracts. Because of the analogous substructure of these compounds to pyochelin, we hypothesized that they may play a role in iron homeostasis or have a biological effect on other bacterial species. Herein, we discuss the physiochemical evaluation of these molecules and disclose, for the first time, their ability to bind iron and promote growth in Pseudomonads.

Enzymatic dimerization in the biosynthetic pathway of microbial natural products

Covering: up to August 2020The dramatic increase in the identification of dimeric natural products generated by microorganisms and plants has played a significant role in drug discovery. The biosynthetic pathways of these products feature inherent dimerization reactions, which are valuable for biosynthetic applications and chemical transformations. The extraordinary mechanisms of the dimerization of secondary metabolites should advance our understanding of the uncommon chemical rules for natural product biosynthesis, which will, in turn, accelerate the discovery of dimeric reactions and molecules in nature and provide promising strategies for the total synthesis of natural products through dimerization. This review focuses on the enzymes involved in the dimerization in the biosynthetic pathway of microbial natural products, with an emphasis on cytochrome P450s, laccases, and intermolecular [4 + 2] cyclases, along with other atypical enzymes. The identification, characterization, and catalytic landscapes of these enzymes are also introduced.

Applying microbial ecology to antimicrobial discovery

Introduction of antibiotics into clinical use has contributed to some of the greatest improvements to public health in the 20th century. Most antibiotics are based on antimicrobials that were isolated from environmental microorganisms over 50 years ago, but emerging resistance requires discovery of new molecules and development of these molecules into therapeutics. Bioinformatic analyses of microbial genomes indicate that many more microbial bioactive molecules remain undiscovered. Understanding when, where, and why these molecules are produced informs efforts to tap into the hidden unexplored chemical diversity. Expanding the search to undersampled ecological niches and improving culturing techniques will ensure discovery of new antibiotics.

A novel semi-selective medium for Pseudomonas protegens isolation from soil samples

Pseudomonas protegens is a rhizosphere pseudomonad with a high agronomical potential (entomopathogenic and beneficial to plants) and bio-catalytic activities, but no selective medium has been described for its isolation. We developed a semi-selective minimum agar medium for the specific isolation and growth of P. protegens. We searched for both (i) a carbon source allowing the growth of P. protegens but potentially inhibiting the growth of other pseudomonads and (ii) an antimicrobial agent suppressing other members of the bacterial rhizosphere community. The M9-PP-agar medium consists of M9 base agar with adipic acid as the only carbon source and Irgasan® as an anti-bacterial agent. We tested the selectivity and sensitivity of M9-PP-agar by measuring the growth of 68 bacterial strains from 36 different species on this medium. Ten of the species tested were able to grow on M9-PP-agar medium: four species from the Pseudomonadaceae (Pseudomonas aeruginosa, Pseudomonas protegens, Pseudomonas putida, Stenotrophomonas maltophilia) as well as Achromobacter xylosoxidans, Agrobacterium tumefaciens, Brevundimonas sp., Serratia liquefaciens, Serratia marcescens and Variovorax paradoxus. All colonies were white, except for those of P. protegens (12 strains), which were typically brown. We demonstrated the efficiency of the M9-PP agar medium for P. protegens isolation, by inoculating two soils with the reference strain P. protegens CHAO^T and then reisolating them. We also developed a fitF-PCR test targeting a regulator gene of the insecticidal P. protegens fit locus, for the rapid molecular detection of P. protegens colonies. We, therefore, developed a highly specific process for the routine isolation of new P. protegens strains from the soil environment, based on the use of a semi-selective medium and the specific color of colonies.

Synthesis and Investigation of the Abiotic Formation of Pyonitrins A-D

Pyonitrins A–D are recently isolated natural products from the insect-associated Pseudomonas protegens strain, which were isolated from complex fractions that exhibited antifungal activity via an in vivo murine candidiasis assay. Genomic studies of Pseudomonas protegens suggested that pyonitrins A–D are formed via a spontaneous nonenzymatic reaction between biosynthetic intermediates of two well-known natural products pyochelin and pyrrolnitrin. Herein we have accomplished the first biomimetic total synthesis of pyonitrins A–D in three steps and studied the nonenzymatic formation of the pyonitrins using ¹⁵N NMR spectroscopy.