Salinosporamide A: a highly cytotoxic proteasome inhibitor from a novel microbial source, a marine bacterium of the new genus salinospora

Microbial Flora Associated with the Halophyte-Salsola imbricate and Its Biotechnical Potential

Halophytes are associated with the intertidal forest ecosystem of Saudi Arabia and seemingly have an immense potential for yielding useful and important natural products. In this study we have aimed to isolate and characterize the endophytic and rhizospheric bacterial communities from the halophyte, Salsola imbricata, In addition these bacterial strains were identified and selected strains were further studied for bioactive secondary metabolites. At least 168 rhizspheric and endophytic bacteria were isolated and of these 22 were active antagonists against the oomycetous fungal plant pathogens, Phytophthora capsici and Pythium ultimum. Active cultures were mainly identified with molecular techniques (16S r DNA) and this revealed 95.7–100% sequence similarities with relevant type strains. These microorgansims were grouped into four major classes: Actinobacteria, Firmicutes, β-Proteobacteria, and γ-Proteobacteria. Production of fungal cell wall lytic enzymes was detected mostly in members of Actinobacteria and Firmicutes. PCR screening for type I polyketide synthases (PKS-I), type II polyketide synthases (PKS-II) and nonribosomal peptide synthetases (NRPS) revealed 13 of the 22 strains (59%) were positive for at least one of these important biosynthetic genes that are known to be involved in the synthesis of important antibiotics. Four bacterial strains of Actinobacteria with potential antagonistic activity including two rhizobacteria, EA52 (Nocardiopsis sp.), EA58 (Pseudonocardia sp.) and two endophytic bacteria Streptomyces sp. (EA65) and Streptomyces sp. (EA67) were selected for secondary metabolite analyses using LC-MS. As a result, the presence of different bioactive compounds in the culture extracts was detected some of which are already reported for their diverse biological activities including antibiotics such as Sulfamethoxypyridazine, Sulfamerazine, and Dimetridazole. In conclusion, this study provides an insight into antagonistic bacterial population especially the Actinobacteria from S. imbricata, producing antifungal metabolites of medical significance and characterized taxonomically in future.

Divergent reactions of oxindoles with amino alcohols via the borrowing hydrogen process: oxindole ring opening vs. C3 alkylation

Oxindoles react with N-acetyl amino alcohols to form tryptamine-derived oxindoles, whereas analogous reactions with N-alkyl amino alcohols lead to lactam formation via a relatively mild borrowing hydrogen process.

Inhibitory Activities of Compounds from the Marine Actinomycete Williamsia sp. MCCC 1A11233 Variant on IgE-Mediated Mast Cells and Passive Cutaneous Anaphylaxis

The compounds of the deep-sea-derived marine Williamsia sp. MCCC 1A11233 (CDMW) were isolated, which are secondary metabolites of the actinomycetes. In this study, seven kinds of CDMW were found to decrease degranulation and histamine release in immunoglobulin E (IgE)-mediated rat basophilic leukemia (RBL)-2H3 cells. The production of cytokines (tumor necrosis factor-α, interleukin-4) was inhibited by these CDMW in RBL-2H3 cells, and their chemical structures were established mainly based on detailed analysis of their NMR spectra. CDMW-3, CDMW-5, and CDMW-15 were further demonstrated to block mast cell-dependent passive cutaneous anaphylaxis in IgE-sensitized mice. Bone marrow mononuclear cells (BMMCs) were established to clarify the effect of CDMW-3, CDMW-5, and CDMW-15 on mast cells. The seven kinds of CDMW decreased the degranulation and histamine release of BMMCs. Furthermore, flow cytometry results indicated that CDMW-3, CDMW-5, and CDMW-15 increased the annexin⁺ cell population of BMMCs. In conclusion, CDMW-3, CDMW-5, and CDMW-15 have obvious antiallergic activity due to induction of the apoptosis of mast cells.

Metal-Free Thermal Activation of Molecular Oxygen Enabled Direct α-CH2-Oxygenation of Free Amines

Direct oxidation of α-CH₂ group of free amines is hard to achieve due to the higher reactivity of amine moiety. Therefore, oxidation of amines involves the use of sophisticated metallic reagents/catalyst in the presence or absence of hazardous oxidants under sensitive reaction conditions. A novel method for direct C-H oxygenation of aliphatic amines through a metal-free activation of molecular oxygen has been developed. Both activated and unactivated free amines were oxygenated efficiently to provide a wide variety of amides (primary, secondary) and lactams under operationally simple conditions without the aid of metallic reagents and toxic oxidants. The method has been applied to the synthesis of highly functionalized amide-containing medicinal drugs, such as O-Me-alibendol and -buclosamide.

Comparative transcriptomics as a guide to natural product discovery and biosynthetic gene cluster functionality

Bacterial natural products remain an important source of new medicines. DNA sequencing has revealed that a majority of natural product biosynthetic gene clusters (BGCs) maintained in bacterial genomes have yet to be linked to the small molecules whose biosynthesis they encode. Efforts to discover the products of these orphan BGCs are driving the development of genome mining techniques based on the premise that many are transcriptionally silent during normal laboratory cultivation. Here, we employ comparative transcriptomics to assess BGC expression among four closely related strains of marine bacteria belonging to the genus Salinispora The results reveal that slightly more than half of the BGCs are expressed at levels that should facilitate product detection. By comparing the expression profiles of similar gene clusters in different strains, we identified regulatory genes whose inactivation appears linked to cluster silencing. The significance of these subtle differences between expressed and silent BGCs could not have been predicted a priori and was only revealed by comparative transcriptomics. Evidence for the conservation of silent clusters among a larger number of strains for which genome sequences are available suggests they may be under different regulatory control from the expressed forms or that silencing may represent an underappreciated mechanism of gene cluster evolution. Coupling gene expression and metabolomics data established a bioinformatic link between the salinipostins and their associated BGC, while genetic manipulation established the genetic basis for this series of compounds, which were previously unknown from Salinispora pacifica.

The ubiquitin-proteasome pathway in adult and pediatric brain tumors: biological insights and therapeutic opportunities

Nearly 20 years ago, the concept of targeting the proteasome for cancer therapy began gaining momentum. This concept was driven by increased understanding of the biology/structure and function of the 26S proteasome, insight into the role of the proteasome in transformed cells, and the synthesis of pharmacological inhibitors with clinically favorable features. Subsequent in vitro, in vivo, and clinical testing culminated in the FDA approval of three proteasome inhibitors-bortezomib, carfilzomib, and ixazomib -for specific hematological malignancies. However, despite in vitro and in vivo studies pointing towards efficacy in solid tumors, clinical responses broadly have been evasive. For brain tumors, a malignancy in dire need of new approaches both in adult and pediatric patients, this has also been the case. Elucidation of proteasome-dependent processes in specific types of brain tumors, the evolution of newer proteasome targeting strategies, and the use of proteasome inhibitors in combination strategies will clarify how these agents can be leveraged more effectively to treat central nervous system malignancies. Since brain tumors represent a heterogeneous subset of solid tumors, and in particular, pediatric brain tumors possess distinct biology from adult brain tumors, tailoring of proteasome inhibitor-based strategies to specific subtypes of these tumors will be critical for advancing care for affected patients, and will be discussed in this review.

A Marine Actinomycete Rescues Caenorhabditis elegans from Pseudomonas aeruginosa Infection through Restitution of Lysozyme 7

The resistance of Pseudomonas aeruginosa to conventional antimicrobial treatment is a major scourge in healthcare. Therefore, it is crucial that novel potent anti-infectives are discovered. The aim of the present study is to screen marine actinomycetes for chemical entities capable of overcoming P. aeruginosa infection through mechanisms involving anti-virulence or host immunity activities. A total of 18 actinomycetes isolates were sampled from marine sediment of Songsong Island, Kedah, Malaysia. Upon confirming that the methanolic crude extract of these isolates do not display direct bactericidal activities, they were tested for capacity to rescue Caenorhabditis elegans infected with P. aeruginosa strain PA14. A hexane partition of the extract from one isolate, designated as Streptomyces sp. CCB-PSK207, could promote the survival of PA14 infected worms by more than 60%. Partial 16S sequence analysis on this isolate showed identity of 99.79% with Streptomyces sundarbansensis. This partition did not impair feeding behavior of C. elegans worms. Tested on PA14, the partition also did not affect bacterial growth or its ability to colonize host gut. The production of biofilm, protease, and pyocyanin in PA14 were uninterrupted, although there was an increase in elastase production. In lys-7::GFP worms, this partition was shown to induce the expression of lysozyme 7, an important innate immunity defense molecule that was repressed during PA14 infection. GC-MS analysis of the bioactive fraction of Streptomyces sp. CCB-PSK207 revealed the presence of methyl esters of branched saturated fatty acids. In conclusion, this is the first report of a marine actinomycete producing metabolites capable of rescuing C. elegans from PA14 through a lys-7 mediated activity.

Natural products and morphogenic activity of γ-Proteobacteria associated with the marine hydroid polyp Hydractinia echinata

Illumina 16S rRNA gene sequencing was used to profile the associated bacterial community of the marine hydroid Hydractinia echinata, a long-standing model system in developmental biology. 56 associated bacteria were isolated and evaluated for their antimicrobial activity. Three strains were selected for further in-depth chemical analysis leading to the identification of 17 natural products. Several γ-Proteobacteria were found to induce settlement of the motile larvae, but only six isolates induced the metamorphosis to the primary polyp stage within 24h. Our study paves the way to better understand how bacterial partners contribute to protection, homeostasis and propagation of the hydroid polyp.

Catalytic Asymmetric Formal [3+2] Cycloaddition of 2-Isocyanatomalonate Esters and Unsaturated Imines: Synthesis of Highly Substituted Chiral γ-Lactams

Unlike their isocyano and isothiocyanato analogues, isocyanato esters remain almost unexplored as formal 1,3-dipoles in asymmetric catalytic reactions. The first asymmetric formal [3+2] cycloaddition involving isocyanato esters and electrophilic alkenes is reported. Diisopropyl 2-isocyanatomalonate reacts with α,β-unsaturated N-(o-anisidyl) imines in the presence of a Mg(OTf)₂ -BOX complex to give highly substituted chiral pyrrolidinones featuring a conjugate exocyclic double bond with excellent yields and enantiomeric excesses up to 99 %. Several transformations of the resulting heterocycles, including the synthesis of a pyroglutamic acid derivative, have been carried out.

Immunoproteasome-selective and non-selective inhibitors: A promising approach for the treatment of multiple myeloma

The ubiquitin-proteasome system (UPS) is the major non-lysosomal proteolytic system for the degradation of abnormal or damaged proteins no longer required. The proteasome is involved in degradation of numerous proteins which regulate the cell cycle, indicating a role in controlling cell proliferation and maintaining cell survival. Defects in the UPS can lead to anarchic cell proliferation and to tumor development. For these reasons UPS inhibition has become a significant new strategy for drug development in cancer treatment. In addition to the constitutive proteasome, which is expressed in all cells and tissues, higher organisms such as vertebrates possess two immune-type proteasomes, the thymoproteasome and the immunoproteasome. The thymoproteasome is specifically expressed by thymic cortical epithelial cells and has a role in positive selection of CD8+ T cells, whereas the immunoproteasome is predominantly expressed in monocytes and lymphocytes and is responsible for the generation of antigenic peptides for cell-mediated immunity. Recent studies demonstrated that the immunoproteasome has a preservative role during oxidative stress and is up-regulated in a number of pathological disorders including cancer, inflammatory and autoimmune diseases. As a consequence, immunoproteasome-selective inhibitors are currently the focus of anticancer drug design. At present, the commercially available proteasome inhibitors bortezomib and carfilzomib which have been validated in multiple myeloma and other model systems, appear to target both the constitutive and immunoproteasomes, indiscriminately. This lack of specificity may, in part, explain some of the side effects of these agents, such as peripheral neuropathy and gastrointestinal effects, which may be due to targeting of the constitutive proteasome in these tissues. In contrast, by selectively inhibiting the immunoproteasome, it may be possible to maintain the antimyeloma and antilymphoma efficacy while reducing these toxicities, thereby increasing the therapeutic index. This review article will be focused on the discussion of the most promising immunoproteasome specific inhibitors which have been developed in recent years. Particular attention will be devoted to the description of their mechanism of action, their structure-activity relationship, and their potential application in therapy.

Enantioselective Synthesis of Functionalized β-Lactones by NHC-Catalyzed Aldol Lactonization of Ketoacids

N-Heterocyclic carbene (NHC)-catalyzed intramolecular aldol lactonization of readily available ketoacids leading to the enantioselective synthesis of cyclopentane-fused β-lactones is presented. The reaction proceeds via the generation of NHC-bound enolate intermediates formed from the ketoacids in the presence of the peptide coupling reagent HATU and NHC generated from the chiral triazolium salt. The functionalized β-lactones are formed under mild conditions in high yields and enantioselectivities.

Rh-Catalyzed Conjugate Addition of Aryl and Alkenyl Boronic Acids to α-Methylene-β-lactones: Stereoselective Synthesis of trans-3,4-Disubstituted β-Lactones

A one-step preparation of 3,4-disubstituted β-lactones through Rh-catalyzed conjugate addition of aryl or alkenyl boronic acids to α-methylene-β-lactones is described. The operationally simple, stereoselective transformation provides a broad range of β-lactones from individual α-methylene-β-lactone templates. This methodology allowed for a direct, final-step C-3 diversification of nocardiolactone, an antimicrobial natural product.

Actinoalloteichus fjordicus sp. nov. isolated from marine sponges: phenotypic, chemotaxonomic and genomic characterisation

Two actinobacterial strains, ADI 127-17^T and GBA 129-24, isolated from marine sponges Antho dichotoma and Geodia barretti, respectively, collected at the Trondheim fjord in Norway, were the subjects of a polyphasic study. According to their 16S rRNA gene sequences, the new isolates were preliminarily classified as belonging to the genus Actinoalloteichus. Both strains formed a distinct branch, closely related to the type strains of Actinoalloteichus hoggarensis and Actinoalloteichus hymeniacidonis, within the evolutionary radiation of the genus Actinoalloteichus in the 16S rRNA gene-based phylogenetic tree. Isolates ADI 127-17^T and GBA 129-24 exhibited morphological, chemotaxonomic and genotypic features distinguishable from their close phylogenetic neighbours. Digital DNA: DNA hybridization and ANI values between strains ADI 127-17^T and GBA 129-24 were 97.6 and 99.7%, respectively, whereas the corresponding values between both tested strains and type strains of their closely related phylogenetic neighbours, A. hoggarensis and A. hymeniacidonis, were well below the threshold for delineation of prokaryotic species. Therefore, strains ADI 127-17^T (= DSM 46855^T) and GBA 129-24 (= DSM 46856) are concluded to represent a novel species of the genus Actinoalloteichus for which the name of Actinoalloteichus fjordicus sp. nov. (type strain ADI 127-17^T = DSM 46855^T = CECT 9355^T) is proposed. The complete genome sequences of the new strains were obtained and compared to that of A. hymeniacidonis DSM 45092^T and A. hoggarensis DSM 45943^T to unravel unique genome features and biosynthetic potential of the new isolates.

Integrated discovery of FOXO1-DNA stabilizers from marine natural products to restore chemosensitivity to anti-EGFR-based therapy for metastatic lung cancer

The transcription factor forkhead box O1 (FOXO1) negatively regulates activated EGFR signaling by turning on the gene expression of tumor suppressor Kruppel-like factor 6. Here, we propose that the chemosensitivity to anti-EGFR-based lung cancer therapy can be restored by stabilization of the FOXO1-DNA complex architecture using small-molecule marine natural medicines. A synthetic protocol that integrates computational ligand-protein-DNA binding analysis and an experimental fluorescence binding assay was applied against a large library of structurally diverse, drug-like marine natural products to discover novel stabilizers of DNA-bound FOXO1 conformation. The screening utilized chemical similarity analysis to exclude structurally redundant compounds, and then carried out high-throughput molecular docking and computational binding analysis to identify potential marine natural product candidates. Consequently, eight commercially available hits were selected and tested in vitro, from which four marine natural product compounds (tanzawaic acid D, hymenidin, cribrostatin 6 and barbamide) were found to have high or moderate potency to selectively bind to the FOXO1 DNA-binding domain (DBD) in the presence of its cognate DNA partner. Atomistic molecular dynamics (MD) simulations revealed that the identified stabilizers do not directly interact with DNA; instead, they can effectively stabilize the free FOXO1 DBD domain in the DNA-bound conformation and thus promote the binding of FOXO1 to DNA.

Microindolinone A, a Novel 4,5,6,7-Tetrahydroindole, from the Deep-Sea-Derived Actinomycete Microbacterium sp. MCCC 1A11207

A novel indole, microindolinone A (1), was isolated from a deep-sea-derived actinomycete Microbacterium sp. MCCC 1A11207, together with 18 known compounds (2-19). By detailed analysis of the ¹H, ¹³C, HSQC, COSY, HMBC, high resolution electron spray ionization mass spectrum (HRESIMS), and circular dichroism (CD) data, the absolute configuration of 1 was elucidated as 5R-hydroxy-4,5,6,7-tetrahydroindole-4-one. It is noteworthy that 1 is the second example of a saturated indole isolated from nature.

Marine Rare Actinobacteria: Isolation, Characterization, and Strategies for Harnessing Bioactive Compounds

Actinobacteria are prolific producers of thousands of biologically active natural compounds with diverse activities. More than half of these bioactive compounds have been isolated from members belonging to actinobacteria. Recently, rare actinobacteria existing at different environmental settings such as high altitudes, volcanic areas, and marine environment have attracted attention. It has been speculated that physiological or biochemical pressures under such harsh environmental conditions can lead to the production of diversified natural compounds. Hence, marine environment has been focused for the discovery of novel natural products with biological potency. Many novel and promising bioactive compounds with versatile medicinal, industrial, or agricultural uses have been isolated and characterized. The natural compounds cannot be directly used as drug or other purposes, so they are structurally modified and diversified to ameliorate their biological or chemical properties. Versatile synthetic biological tools, metabolic engineering techniques, and chemical synthesis platform can be used to assist such structural modification. This review summarizes the latest studies on marine rare actinobacteria and their natural products with focus on recent approaches for structural and functional diversification of such microbial chemicals for attaining better applications.

A strategy for dual inhibition of the proteasome and fatty acid synthase with belactosin C-orlistat hybrids

The proteasome, a validated cellular target for cancer, is central for maintaining cellular homeostasis, while fatty acid synthase (FAS), a novel target for numerous cancers, is responsible for palmitic acid biosynthesis. Perturbation of either enzymatic machine results in decreased proliferation and ultimately cellular apoptosis. Based on structural similarities, we hypothesized that hybrid molecules of belactosin C, a known proteasome inhibitor, and orlistat, a known inhibitor of the thioesterase domain of FAS, could inhibit both enzymes. Herein, we describe proof-of-principle studies leading to the design, synthesis and enzymatic activity of several novel, β-lactone-based, dual inhibitors of these two enzymes. Validation of dual enzyme targeting through activity-based proteome profiling with an alkyne probe modeled after the most potent inhibitor, and preliminary serum stability studies of selected derivatives are also described. These results provide proof of concept for dual targeting of the proteasome and fatty acid synthase-thioesterase (FAS-TE) enabling a new approach for the development of drug-candidates with potential to overcome resistance.

Rare Polyene-polyol Macrolides from Mangrove-derived Streptomyces sp. ZQ4BG

Bioactive natural products from mangrove-derived actinomycetes are important sources for discovery of drug lead compounds. In this study, an extract prepared from culture of an actinomycete Streptomyces sp. ZQ4BG isolated from mangrove soils was found to have activity in inhibiting proliferation of glioma cells. Large culture of this mangrove actinomycete in Gause’s liquid medium resulted in isolation of seven novel polyene-polyol macrolides, named as flavofungins III–IX (3–9), together with known flavofungins I (1) and II (2) and spectinabilin (10). Structures of these isolated compounds were elucidated by extensive NMR analyses and HRESIMS data. The stereochemical assignments were achieved by a combination of NOE information, universal NMR database, and chemical reactions including preparation of acetonide derivatives and Mosher esters. Flavofungins IV–VIII (4–8) are rare 32-membered polyene-polyol macrolides with a tetrahydrofuran ring, while flavofungin IX (9) represents the first example of this type of macrolide with a unique oxepane ring. Flavofungins I (1) and II (2) and spectinabilin (10) showed anti-glioma and antifungal activities.

Streptomyces artemisiae MCCB 248 isolated from Arctic fjord sediments has unique PKS and NRPS biosynthetic genes and produces potential new anticancer natural products

After screening marine actinomycetes isolated from sediment samples collected from the Arctic fjord Kongsfjorden for potential anticancer activity, an isolate identified as Streptomyces artemisiae MCCB 248 exhibited promising results against the NCI-H460 human lung cancer cell line. H460 cells treated with the ethyl acetate extract of strain MCCB 248 and stained with Hoechst 33342 showed clear signs of apoptosis, including shrinkage of the cell nucleus, DNA fragmentation and chromatin condensation. Further to this treated cells showed indications of early apoptotic cell death, including a significant proportion of Annexin V positive staining and evidence of DNA damage as observed in the TUNEL assay. Amplified PKS 1 and NRPS genes involved in secondary metabolite production showed only 82% similarity to known biosynthetic genes of Streptomyces, indicating the likely production of a novel secondary metabolite in this extract. Additionally, chemical dereplication efforts using LC–MS/MS molecular networking suggested the presence of a series of undescribed tetraene polyols. Taken together, these results revealed that this Arctic S. artemisiae strain MCCB 248 is a promising candidate for natural products drug discovery and genome mining for potential anticancer agents.

Enzymatic Halogenation and Dehalogenation Reactions: Pervasive and Mechanistically Diverse

Naturally produced halogenated compounds are ubiquitous across all domains of life where they perform a multitude of biological functions and adopt a diversity of chemical structures. Accordingly, a diverse collection of enzyme catalysts to install and remove halogens from organic scaffolds has evolved in nature. Accounting for the different chemical properties of the four halogen atoms (fluorine, chlorine, bromine, and iodine) and the diversity and chemical reactivity of their organic substrates, enzymes performing biosynthetic and degradative halogenation chemistry utilize numerous mechanistic strategies involving oxidation, reduction, and substitution. Biosynthetic halogenation reactions range from simple aromatic substitutions to stereoselective C-H functionalizations on remote carbon centers and can initiate the formation of simple to complex ring structures. Dehalogenating enzymes, on the other hand, are best known for removing halogen atoms from man-made organohalogens, yet also function naturally, albeit rarely, in metabolic pathways. This review details the scope and mechanism of nature's halogenation and dehalogenation enzymatic strategies, highlights gaps in our understanding, and posits where new advances in the field might arise in the near future.

Novel Proteasome Inhibitors and Histone Deacetylase Inhibitors: Progress in Myeloma Therapeutics

The unfolded protein response is responsible for the detection of misfolded proteins and the coordination of their disposal and is necessary to maintain the cellular homoeostasis. Multiple myeloma cells secrete large amounts of immunoglobulins, proteins that need to be correctly folded by the chaperone system. If this process fails, the misfolded proteins have to be eliminated by the two main garbage-disposal systems of the cell: proteasome and aggresome. The blockade of either of these systems will result in accumulation of immunoglobulins and other toxic proteins in the cytoplasm and cell death. The simultaneous inhibition of the proteasome, by proteasome inhibitors (PIs) and the aggresome, by histone deacetylase inhibitors (HDACi) results in a synergistic increase in cytotoxicity in myeloma cell lines. This review provides an overview of mechanisms of action of second-generation PIs and HDACi in multiple myeloma (MM), the clinical results currently observed with these agents and assesses the potential therapeutic impact of the different agents in the two classes. The second-generation PIs offer benefits in terms of increased efficacy, reduced neurotoxicity as off-target effect and may overcome resistance to bortezomib because of their different chemical structure, mechanism of action and biological properties. HDACi with anti-myeloma activity in clinical development discussed in this review include vorinostat, panobinostat and selective HDAC6 inhibitor, ricolinostat.

Rapid Enrichment of Dehalococcoides-Like Bacteria by Partial Hydrophobic Separation

Organohalide-respiring bacteria can be difficult to enrich and isolate, which can limit research on these important organisms. The goal of this research was to develop a method to rapidly (minutes to days) enrich these organisms from a mixed community. The method presented is based on the hypothesis that organohalide-respiring bacteria would be more hydrophobic than other bacteria as they dehalogenate hydrophobic compounds. The method developed tests this hypothesis by separating a portion of putative organohalide-respiring bacteria, those phylogenetically related to Dehalococcoides mccartyi, at the interface between a hydrophobic organic solvent and an aqueous medium. This novel partial separation technique was tested with a polychlorinated biphenyl-enriched sediment-free culture, a tetrachloroethene-enriched digester sludge culture, and uncontaminated lake sediment. Significantly higher fractions, up to 20.4 times higher, of putative organohalide-respiring bacteria were enriched at the interface between the medium and either hexadecane or trichloroethene. The selective partial separation of these putative organohalide-respiring bacteria occurred after 20 min, strongly suggesting that the separation was a result of physical-chemical interactions between the cell surface and hydrophobic solvent. Dechlorination activity postseparation was verified by the production of cis-dichloroethene when amended with tetrachloroethene. A longer incubation time of 6 days prior to separation with trichloroethene increased the total number of putative organohalide-respiring bacteria. This method provides a way to quickly separate some of the putative organohalide-respiring bacteria from other bacteria, thereby improving our ability to study multiple and different bacteria of potential interest and improving knowledge of these bacteria.IMPORTANCE Organohalide-respiring bacteria, bacteria capable of respiring chlorinated contaminants, can be difficult to enrich, which can limit their predictable use for the bioremediation of contaminated sites. This paper describes a method to quickly separate Dehalococcoides-like bacteria, a group of organisms containing organohalide-respiring bacteria, from other bacteria in a mixed community. From this work, Dehalococcoides-like bacteria appear to have a hydrophobic cell surface, facilitating a rapid (20 min) partial separation from a mixed culture at the surface of a hydrophobic liquid. This method was verified in a polychlorinated biphenyl-enriched sediment-free culture, an anaerobic digester sludge, and uncontaminated sediment. The method described can drastically reduce the amount of time required to partially separate Dehalococcoides-like bacteria from a complex mixed culture, improving researchers' ability to study these important bacteria.

Construction of Fused Pyrrolidines and β-Lactones by Carbene-Catalyzed C-N, C-C, and C-O Bond Formations

A carbene-catalyzed intermolecular C-N bond formation, which initiates a highly selective cascade reaction for the synthesis of pyrrolidine fused β-lactones, is disclosed. The nitrogen-containing bicyclic β-lactone products are obtained with good yields and excellent stereoselectivities. Synthetic transformations of the reaction products into useful functional molecules, such as amino catalysts, can be efficiently realized under mild reaction conditions. Mechanistically, this study provides insights into modulating the reactivities of heteroatoms, such as nitrogen atoms, in challenging carbene-catalyzed asymmetric carbon-heteroatom bond-forming reactions.

Enantioselective Narasaka-Heck cyclizations: synthesis of tetrasubstituted nitrogen-bearing stereocenters

The first examples of highly enantioselective Narasaka-Heck cyclizations are described. A SPINOL-derived P,N-ligand system enables Pd-catalyzed 5-exo cyclization of a range of oxime esters with sterically diverse trisubstituted alkenes to generate dihydropyrroles containing tetrasubstituted nitrogen-bearing stereocenters in 56 to 86% yield and 90 : 10 to 95 : 5 e.r. These processes are rare examples of reactions that proceed via enantioselective migratory insertion of alkenes into Pd-N bonds, and the first where trisubstituted alkenes are used to generate tetrasubstituted stereocenters with high enantioselectivity.

Antagonistic Activity and Mode of Action of Phenazine-1-Carboxylic Acid, Produced by Marine Bacterium Pseudomonas aeruginosa PA31x, Against Vibrio anguillarum In vitro and in a Zebrafish In vivo Model

Phenazine and its derivatives are very important secondary metabolites produced from Pseudomonas spp. and have exhibited broad-spectrum antifungal and antibacterial activities. However, till date, there are few reports about marine derived Pseudomonas and its production of phenazine metabolites. In this study, we isolated a marine Pseudomonas aeruginosa strain PA31x which produced natural product inhibiting the growth of Vibrio anguillarum C312, one of the most serious bacterial pathogens in marine aquaculture. Combining high-resolution electro-spray-ionization mass spectroscopy and nuclear magnetic resonance spectroscopy analyses, the functional compound against V. anguillarum was demonstrated to be phenazine-1-carboxylic acid (PCA), an important phenazine derivative. Molecular studies indicated that the production of PCA by P. aeruginosa PA31x was determined by gene clusters phz1 and phz2 in its genome. Electron microscopic results showed that treatment of V. anguillarum with PCA developed complete lysis of bacterial cells with fragmented cytoplasm being released to the surrounding environment. Additional evidence indicated that reactive oxygen species generation preceded PCA-induced microbe and cancer cell death. Notably, treatment with PCA gave highly significant protective activities against the development of V. anguillarum C312 on zebrafish. Additionally, the marine derived PCA was further found to effectively inhibit the growth of agricultural pathogens, Acidovorax citrulli NP1 and Phytophthora nicotianae JM1. Taken together, this study reveals that marine Pseudomonas derived PCA carries antagonistic activities against both aquacultural and agricultural pathogens, which broadens the application fields of PCA.

β-Lactone Synthetase Found in the Olefin Biosynthesis Pathway

The first β-lactone synthetase enzyme is reported, creating an unexpected link between the biosynthesis of olefinic hydrocarbons and highly functionalized natural products. The enzyme OleC, involved in the microbial biosynthesis of long-chain olefinic hydrocarbons, reacts with syn- and anti-β-hydroxy acid substrates to yield cis- and trans-β-lactones, respectively. Protein sequence comparisons reveal that enzymes homologous to OleC are encoded in natural product gene clusters that generate β-lactone rings, suggesting a common mechanism of biosynthesis.

Intermolecular cascade annulations of N-(arylsulfonyl)acrylamides with dual C(sp3)–H bonds: divergent access to indanes and pyrrolidin-2-ones

A new divergent cascade annulation reaction of N-(arylsulfonyl)acrylamides and dual alkyl C(sp³)–H bonds for selectively producing indanes and pyrrolidin-2-ones is presented.

Recent advances in the Overman rearrangement: synthesis of natural products and valuable compounds

This review documents the reports since 2005 on the Overman rearrangement, an important C–N bond forming reaction that has been profoundly used in the synthesis of natural products, synthetic intermediates, building blocks and valuable compounds.

Catalysis by solvation rather than the desolvation effect: exploring the catalytic efficiency of SAM-dependent chlorinase

Chlorinase SalL active sites provide electrostatic stabilization of the transition state which is the origin of its catalytic effect.

Complete genome sequence of the actinomycete Actinoalloteichus hymeniacidonis type strain HPA 177T isolated from a marine sponge

Actinoalloteichus hymeniacidonis HPA 177T is a Gram-positive, strictly aerobic, black pigment producing and spore-forming actinomycete, which forms branching vegetative hyphae and was isolated from the marine sponge Hymeniacidon perlevis. Actinomycete bacteria are prolific producers of secondary metabolites, some of which have been developed into anti-microbial, anti-tumor and immunosuppressive drugs currently used in human therapy. Considering this and the growing interest in natural products as sources of new drugs, actinomycete bacteria from the hitherto poorly explored marine environments may represent promising sources for drug discovery. As A. hymeniacidonis, isolated from the marine sponge, is a type strain of the recently described and rare genus Actinoalloteichus, knowledge of the complete genome sequence enables genome analyses to identify genetic loci for novel bioactive compounds. This project, describing the 6.31 Mbp long chromosome, with its 5346 protein-coding and 73 RNA genes, will aid the Genomic Encyclopedia of Bacteria and Archaea project.