Modular strategies for structure and function employed by marine cyanobacteria: characterization and synthesis of pitinoic acids

Eco-friendly biopesticides derived from CO2-Fixing cyanobacteria

There is currently an escalating global demand for the utilization of plant and natural extracts as pesticides due to their minimal health risks. Cyanobacteria are highly valuable organisms with significant potential in agriculture and are of great interest for the development of agrochemical agents as biopesticides. The flexibility and adaptability of Cyanobacteria to various environmental conditions are facilitated by the presence of specialized enzymes involved in the production of biologically active diverse secondary metabolites, including alkaloids, lipopolysaccharides, non-protein amino acids, non-ribosomal peptides, polyketides, terpenoids, and others. This review focuses on the metabolites synthesized from cyanobacteria that have demonstrated effectiveness as antibacterial, antiviral, antifungal agents, insecticides, herbicides, and more. The potential role of cyanobacteria as an alternative to chemical pesticides for environmental conservation is discussed.

Cyclopropane-Containing Specialized Metabolites from the Marine Cyanobacterium cf. Lyngbya sp

Marine cyanobacteria are known to produce structurally diverse bioactive specialized metabolites during bloom occurrence. These ecologically active allelochemicals confer chemical defense for the microalgae from competing microbes and herbivores. From a collection of a marine cyanobacterium, cf. Lyngbya sp., a small quantity of a new cyclopropane-containing molecule, benderadiene (2), and lyngbyoic acid (1) were purified and characterized using spectroscopic methods. Using live reporter quorum-sensing (QS) inhibitory assays, based on P. aeruginosa PAO1 lasB-gfp and rhlA-gfp strains, both compounds were found to inhibit QS-regulated gene expression in a dose-dependent manner. In addition to lyngbyoic acid being more active in the PAO1 lasB-gfp biosensor strain (IC₅₀ of 20.4 µM), it displayed anti-biofilm activity when incubated with wild-type P. aeruginosa. The discovery of lyngbyoic acid in relatively high amounts provided insights into its ecological significance as a defensive allelochemical in targeting competing microbes through interference with their QS systems and starting material to produce other related analogs. Similar strategies could be adopted by other marine cyanobacterial strains where the high production of other lipid acids has been reported. Preliminary evidence is provided from the virtual molecular docking of these cyanobacterial free acids at the ligand-binding site of the P. aeruginosa LasR transcriptional protein.

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.

Heterologous production of cyanobacterial compounds

Cyanobacteria produce a plethora of compounds with unique chemical structures and diverse biological activities. Importantly, the increasing availability of cyanobacterial genome sequences and the rapid development of bioinformatics tools have unraveled the tremendous potential of cyanobacteria in producing new natural products. However, the discovery of these compounds based on cyanobacterial genomes has progressed slowly as the majority of their corresponding biosynthetic gene clusters (BGCs) are silent. In addition, cyanobacterial strains are often slow-growing, difficult for genetic engineering, or cannot be cultivated yet, limiting the use of host genetic engineering approaches for discovery. On the other hand, genetically tractable hosts such as Escherichia coli, Actinobacteria, and yeast have been developed for the heterologous expression of cyanobacterial BGCs. More recently, there have been increased interests in developing model cyanobacterial strains as heterologous production platforms. Herein, we present recent advances in the heterologous production of cyanobacterial compounds in both cyanobacterial and noncyanobacterial hosts. Emerging strategies for BGC assembly, host engineering, and optimization of BGC expression are included for fostering the broader applications of synthetic biology tools in the discovery of new cyanobacterial natural products.

Ambigols from the Cyanobacterium Fischerella ambigua Increase Prodigiosin Production in Serratia spp

When a library of 573 cyanobacteria extracts was screened for inhibition of the quorum sensing regulated prodigiosin production of Serratia marcescens, an extract of the cyanobacterium Fischerella ambigua (Näg.) Gomont 108b was found to drastically increase prodigiosin production. Bioactivity-guided isolation of the active compounds resulted in the two new natural products ambigol D and E along with the known ambigols A and C. Ambigol C treatment increased prodiginine production of Serratia sp. ATCC 39006 (S39006) by a factor of 10, while ambigols A and D were found to have antibiotic activity against this strain. The RNA-Seq of S39006 treated with ambigol C and subsequent differential gene expression and functional enrichment analyses indicated a significant downregulation of genes associated with the translation machinery and fatty acid biosynthesis in Serratia, as well as increased expression of genes related to the uptake of l-proline. These results suggest that the ambigols increase prodiginine production in S39006 not by activating the SmaIR quorum sensing system but possibly by increasing the precursor supply of l-proline and malonyl-CoA.

Traditional Chinese Medicine Prescriptions Decrease Diarrhea Rate by Relieving Colonic Inflammation and Ameliorating Caecum Microbiota in Piglets

Diarrhea is a leading cause of death in piglets. XiaoJianZhong (XJZ) and Jingsananli-sepsis (JSS) were two traditional Chinese medicine (TCM) prescriptions to prevent and treat intestinal diseases, including diarrhea and inflammatory disease. Here, we investigated the effects of XJZ and JSS on diarrhea rate, growth performance, colonic inflammation, and caecum microbiota in piglets. A total of 18 piglets were selected and randomly divided into three groups. Control group was supplied with basal diets, while TCM1 and TCM2 groups were, respectively, supplied with XJZ and JSS in basal diets. Decreased diarrhea rate, colonic or caecal pH, and elevated apparent nutrient digestibility were observed in both TCM groups. Meanwhile, both prescriptions alleviated colonic inflammation by decreasing mRNA expression of proinflammatory cytokines and suppressing the TLR4/MyD88/NF-κB signaling pathway. Additionally, TCM1 and TCM2 prescriptions ameliorated caecum microbiota composition and increased the abundance of beneficial bacteria, together with regulations on several genes that are responsible for signaling pathways involved in cancers and metabolic diseases. Importantly, both TCM1 and TCM2 significantly promoted the average daily gain (ADG) and reduced the feed : gain (F : G) ratio. In conclusion, both TCM prescriptions effectively decreased diarrhea rate and increased growth performance by elevating apparent nutrient digestibility and gut health, via relieving colonic inflammation and ameliorating gut microbiota composition of piglets.

Discovery and Total Synthesis of Doscadenamide A: A Quorum Sensing Signaling Molecule from a Marine Cyanobacterium

Quorum sensing (QS) plays a critical role in the regulation of bacterial pathogenesis. Doscadenamide A (1a) was isolated from a marine cyanobacterium, its structure elucidated by NMR, and its activity linked to QS induction. The total synthesis of 1a was developed, and the absolute configuration confirmed through comparison of the isolated natural product with synthetic diastereomers. Our preliminary investigation indicated that 1a could activate QS signaling in a LasR-dependent manner.

Widespread Existence of Quorum Sensing Inhibitors in Marine Bacteria: Potential Drugs to Combat Pathogens with Novel Strategies

Quorum sensing (QS) is a phenomenon of intercellular communication discovered mainly in bacteria. A QS system consisting of QS signal molecules and regulatory protein components could control physiological behaviors and virulence gene expression of bacterial pathogens. Therefore, QS inhibition could be a novel strategy to combat pathogens and related diseases. QS inhibitors (QSIs), mainly categorized into small chemical molecules and quorum quenching enzymes, could be extracted from diverse sources in marine environment and terrestrial environment. With the focus on the exploitation of marine resources in recent years, more and more QSIs from the marine environment have been investigated. In this article, we present a comprehensive review of QSIs from marine bacteria. Firstly, screening work of marine bacteria with potential QSIs was concluded and these marine bacteria were classified. Afterwards, two categories of marine bacteria-derived QSIs were summarized from the aspects of sources, structures, QS inhibition mechanisms, environmental tolerance, effects/applications, etc. Next, structural modification of natural small molecule QSIs for future drug development was discussed. Finally, potential applications of QSIs from marine bacteria in human healthcare, aquaculture, crop cultivation, etc. were elucidated, indicating promising and extensive application perspectives of QS disruption as a novel antimicrobial strategy.

Alteration of Gut Microbiota and Inflammatory Cytokine/Chemokine Profiles in 5-Fluorouracil Induced Intestinal Mucositis

Disturbed homeostasis of gut microbiota has been suggested to be closely associated with 5-fluorouracil (5-Fu) induced mucositis. However, current knowledge of the overall profiles of 5-Fu-disturbed gut microbiota is limited, and so far there is no direct convincing evidence proving the causality between 5-Fu-disturbed microbiota and colonic mucositis. In mice, in agreement with previous reports, 5-Fu resulted in severe colonic mucositis indicated by weight loss, diarrhea, bloody stool, shortened colon, and infiltration of inflammatory cells. It significantly changed the profiles of inflammatory cytokines/chemokines in serum and colon. Adhesion molecules such as vascular cell adhesion molecule-1 (VCAM-1), intercellular adhesion molecule-1 (ICAM-1), and VE-Cadherin were increased. While tight junction protein occludin was reduced, however, zonula occludens-1 (ZO-1) and junctional adhesion molecule-A (JAM-A) were increased in colonic tissues of 5-Fu treated mice. Meanwhile, inflammation related signaling pathways including NF-κB and mitogen activated protein kinase (MAPKs) in the colon were activated. Further study disclosed that 5-Fu diminished bacterial community richness and diversity, leading to the relative lower abundance of Firmicutes and decreased Firmicutes/Bacteroidetes (F/B) ratio in feces and cecum contents. 5-Fu also reduced the proportion of Proteobacteria, Tenericutes, Cyanobacteria, and Candidate division TM7, but increased that of Verrucomicrobia and Actinobacteria in feces and/or cecum contents. The fecal transplant from healthy mice prevented body weight loss and colon shortening of 5-Fu treated mice. In addition, the fecal transplant from 5-Fu treated mice reduced body weight and colon length of vancomycin-pretreated mice. Taken together, our study demonstrated that gut microbiota was actively involved in the pathological process of 5-Fu induced intestinal mucositis, suggesting potential attenuation of 5-Fu induced intestinal mucositis by manipulating gut microbiota homeostasis.

Quorum Sensing Inhibitors from the Sea Discovered Using Bacterial N-acyl-homoserine Lactone-Based Biosensors

Marine natural products with antibiotic activity have been a rich source of drug discovery; however, the emergence of antibiotic-resistant bacterial strains has turned attention towards the discovery of alternative innovative strategies to combat pathogens. In many pathogenic bacteria, the expression of virulence factors is under the regulation of quorum sensing (QS). QS inhibitors (QSIs) present a promising alternative or potential synergistic treatment since they disrupt the signaling pathway used for intra- and interspecies coordination of expression of virulence factors. This review covers the set of molecules showing QSI activity that were isolated from marine organisms, including plants (algae), animals (sponges, cnidarians, and bryozoans), and microorganisms (bacteria, fungi, and cyanobacteria). The compounds found and the methods used for their isolation are the emphasis of this review.

Kinetically controlled E-selective catalytic olefin metathesis

A major shortcoming in olefin metathesis, a chemical process that is central to research in several branches of chemistry, is the lack of efficient methods that kinetically favor E isomers in the product distribution. Here we show that kinetically E-selective cross-metathesis reactions may be designed to generate thermodynamically disfavored alkenyl chlorides and fluorides in high yield and with exceptional stereoselectivity. With 1.0 to 5.0 mole % of a molybdenum-based catalyst, which may be delivered in the form of air- and moisture-stable paraffin pellets, reactions typically proceed to completion within 4 hours at ambient temperature. Many isomerically pure E-alkenyl chlorides, applicable to catalytic cross-coupling transformations and found in biologically active entities, thus become easily and directly accessible. Similarly, E-alkenyl fluorides can be synthesized from simpler compounds or more complex molecules.

Biological targets and mechanisms of action of natural products from marine cyanobacteria

Marine cyanobacteria are an ancient group of organisms and prolific producers of bioactive secondary metabolites. These compounds are presumably optimized by evolution over billions of years to exert high affinity for their intended biological target in the ecologically relevant organism but likely also possess activity in different biological contexts such as human cells. Screening of marine cyanobacterial extracts for bioactive natural products has largely focused on cancer cell viability; however, diversification of the screening platform led to the characterization of many new bioactive compounds. Targets of compounds have oftentimes been elusive if the compounds were discovered through phenotypic assays. Over the past few years, technology has advanced to determine mechanism of action (MOA) and targets through reverse chemical genetic and proteomic approaches, which has been applied to certain cyanobacterial compounds and will be discussed in this review. Some cyanobacterial molecules are the most-potent-in-class inhibitors and therefore may become valuable tools for chemical biology to probe protein function but also be templates for novel drugs, assuming in vitro potency translates into cellular and in vivo activity. Our review will focus on compounds for which the direct targets have been deciphered or which were found to target a novel pathway, and link them to disease states where target modulation may be beneficial.

Marine natural products

This review covers the literature published in 2013 for marine natural products (MNPs), with 982 citations (644 for the period January to December 2013) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1163 for 2013), together with the relevant biological activities, source organisms and country of origin. Reviews, biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included.

Biological Activity of Recently Discovered Halogenated Marine Natural Products

This review presents the biological activity-antibacterial, antifungal, anti-parasitic, antiviral, antitumor, antiinflammatory, antioxidant, and enzymatic activity-of halogenated marine natural products discovered in the past five years. Newly discovered examples that do not report biological activity are not included.

Quorum quenching agents: resources for antivirulence therapy

The continuing emergence of antibiotic-resistant pathogens is a concern to human health and highlights the urgent need for the development of alternative therapeutic strategies. Quorum sensing (QS) regulates virulence in many bacterial pathogens, and thus, is a promising target for antivirulence therapy which may inhibit virulence instead of cell growth and division. This means that there is little selective pressure for the evolution of resistance. Many natural quorum quenching (QQ) agents have been identified. Moreover, it has been shown that many microorganisms are capable of producing small molecular QS inhibitors and/or macromolecular QQ enzymes, which could be regarded as a strategy for bacteria to gain benefits in competitive environments. More than 30 species of marine QQ bacteria have been identified thus far, but only a few of them have been intensively studied. Recent studies indicate that an enormous number of QQ microorganisms are undiscovered in the highly diverse marine environments, and these marine microorganism-derived QQ agents may be valuable resources for antivirulence therapy.