Selective Isolation and Screening of Soil Microorganisms for Metabolites with Herbicidal Potential

Summary

Crop losses from weeds worldwide average 10% annually. Herbicide application is almost essential in modern agriculture to maintain high productivity. Increased awareness of the environmental damage caused by continued use of conventional synthetic herbicides has aroused great interest in biodegradable, selective and environmentally friendly herbicides. The increasing incidence of herbicide resistance in weeds has stimulated research for herbicidal compounds with new or novel sites and modes of action. Microbial metabolites have become the focus of attention of researchers searching for natural product alternatives to conventional herbicides. Two well-known commercial herbicides of microbial origin are anisomycin (commercial analogue, methoxyphenon) and bialaphos. Both were isolated from members of actinomycetes. Several phytotoxins have been isolated from microbial metabolites, e.g., herbicidins A and B, herbimycins A and B, nigericin, tentoxin and others. The list of microbial phytotoxins continues to increase. Actinomycetes are the major source of several herbicides and other bioactive compounds. The potential of discovering new phytotox-ins from metabolites of microorganisms is still unlimited. Methods of isolation of actinomycetes, their screening for phytotoxins, separation of phytotoxins from metabolites and partial purification of the toxins are described. Included are screening of soil fungi for phytotoxin, mass culture of fungi, and bioassays.     

The search for new natural herbicides – Strategic approaches for discovering fungal phytotoxins

Plant pathogens produce toxic metabolites which may play a role in affecting their plant hosts by the development of diseases. Such compounds present considerable potential as models for developing herbicides with new modes of action unrelated to those in current use. This study provides an overview on the chemical ecology of plant-pathogenic fungi interactions as a promising approach for discovering new molecules possessing herbicide activity, along with the main research strategies currently employed for the isolation and identification of such compounds. The steps involved in: a) isolating fungal phytotoxic metabolites; b) the factors affecting in vitro biosynthesis of phytotoxins, extraction and fractionation methods; c) the bioassay-guided fractionation procedure, and d) the bioassays most commonly used for monitoring isolation processes, are discussed.     

Weed control in conservation agriculture systems of Zimbabwe: Identifying economical best strategies

Weed management under conservation agriculture (CA), especially when manually controlled is one of the major setbacks for the widespread adoption of CA in southern Africa. This study was conducted at three on-station and three on-farm sites: CIMMYT-Harare, Domboshawa Training Centre and Henderson Research Station (on-station sites), Hereford farm, Madziva communal area and Shamva communal area (on-farm sites). The evaluation focused on the effect of initial herbicide application and succeeding manual weeding whenever weeds were 10 cm tall or 10 cm in length for grasses with stoloniferous–rhizomatous growth habit. Weeds counts, weeding time and grain yields were collected at all on-station sites. At the on-farm sites, weed counts were done before weeding and a number of farmers were timed during weeding. The results showed that herbicides use reduced the weed density and time taken on weeding at all sites. Combining herbicides e.g. atrazine, glyphosate and metalachlor had the lowest weed density and weeding time at all sites. However, the treatments had no effect on maize grain yields suggesting that appropriate and timely manual weeding reduced crop/weed competition. Herbicides treatments had higher input costs than manual weeding due to the additional cost of herbicide but the treatment with manual weeding only had more overall labour days compared to the mixture of three herbicides. In order to achieve economic benefits, smallholder farmers may use the time for value addition e.g. expand cropped land area, use time for value addition, or sell new products on the market. Herbicides use reduces the manual labour needed to control weeds and minimise total crop failure due to untimely weeding hence, herbicides are an important but not the only weed control option under CA systems in Zimbabwe.     

Lignin and polyphenols as allelochemicals

By the microbiological action, lignin from vegetal wastes is transformed at soil level in organic prebiotic products with physiological activity on plants development. On the other hand, some micromolecular compounds resulted from plant wastes decomposition, along with polyphenols coming from extraction of plant residues could play a role of allelochemicals. The understanding of the allelochemical action mechanisms allow us to use these compounds to enhance crop production and develop a more sustainable agriculture, including weed and pest control through crop rotations, residue management and a variety of approaches in biocontrol. Other goals are to adopt allelochemicals as herbicides, pesticides and growth stimulants, modify crop genomes to manipulate allelochemicals production and better elucidate chemical communications between the components of ecosystem. The result obtained in the utilization of lignins and polyphenols as allelochemicals are presented in this review.     

Targeting Nuclear Receptors with Marine Natural Products

Nuclear receptors (NRs) are important pharmaceutical targets because they are key regulators of many metabolic and inflammatory diseases, including diabetes, dyslipidemia, cirrhosis, and fibrosis. As ligands play a pivotal role in modulating nuclear receptor activity, the discovery of novel ligands for nuclear receptors represents an interesting and promising therapeutic approach. The search for novel NR agonists and antagonists with enhanced selectivities prompted the exploration of the extraordinary chemical diversity associated with natural products. Recent studies involving nuclear receptors have disclosed a number of natural products as nuclear receptor ligands, serving to re-emphasize the translational possibilities of natural products in drug discovery. In this review, the natural ligands of nuclear receptors will be described with an emphasis on their mechanisms of action and their therapeutic potentials, as well as on strategies to determine potential marine natural products as nuclear receptor modulators.     

Altered target sites as a mechanism of herbicide resistance

Over 200 distinct herbicide resistant weed biotypes have evolved worldwide. In most of these, resistance is conferred by an altered target site, i.e. a modified target protein with reduced affinity for the herbicide(s) in question. This has been documented for herbicides that target most major known sites of action, including those that inhibit photosynthetic electron transfer at photosystem II, acetyl-CoA carboxylase, acetolactate synthase, and tubulin polymerization. Patterns of cross-resistance to structurally similar herbicides and those from other chemical classes that target the same site vary, depending on the mutation and its effect on protein steric and electronic properties. Mechanisms of target site-based herbicide resistance are reviewed, with emphasis on the biochemical and molecular basis for resistance.     

油菜抗除草剂机理与种质创制研究进展

杂草是制约油菜生产的重要生物灾害之一,严重影响油菜的产量和品质。培育抗除草剂油菜品种是防除油菜田间杂草的经济、有效的途径。本文综述了已被广泛应用的草甘膦、草铵膦和ALS酶抑制类除草剂的作用机理、植物对除草剂产生抗性的机制以及国内外这三类油菜抗性种质的创制和研究进展,并提出了油菜抗除草剂种质的发展策略,加强抗性机制研究和基因的发掘力度,利用基因编辑等新技术创制抗除草剂油菜新种质,培育具有多种除草剂抗性的油菜新品种。     

Metabolites from Marine-Derived Fungi as Potential Antimicrobial Adjuvants

Marine-derived fungi constitute an interesting source of bioactive compounds, several of which exhibit antibacterial activity. These acquire special importance, considering that antimicrobial resistance is becoming more widespread. The overexpression of efflux pumps, capable of expelling antimicrobials out of bacterial cells, is one of the most worrisome mechanisms. There has been an ongoing effort to find not only new antimicrobials, but also compounds that can block resistance mechanisms which can be used in combination with approved antimicrobial drugs. In this work, a library of nineteen marine natural products, isolated from marine-derived fungi of the genera Neosartorya and Aspergillus, was evaluated for their potential as bacterial efflux pump inhibitors as well as the antimicrobial-related mechanisms, such as inhibition of biofilm formation and quorum-sensing. Docking studies were performed to predict their efflux pump action. These compounds were also tested for their cytotoxicity in mouse fibroblast cell line NIH/3T3. The results obtained suggest that the marine-derived fungal metabolites are a promising source of compounds with potential to revert antimicrobial resistance and serve as an inspiration for the synthesis of new antimicrobial drugs.     

Weed control research in Colorado potatoes—A review

Studies have been conducted for three years to determine the herbicides best adapted for the control of annual broadleaf and grass weeds in Colorado potato fields. The most effective registered herbicides are EPTC, EPTC + trifluralin, and metobromuron. Promising herbicides that are not registered are alachlor and 4-amino-6-t-butyl-3-(methylthio)-as-triazin-5-(4H)-one (BAY-94337). These experiments show the efficacy of several herbicides. The data indicate little need for the presently accepted pattern of extensive post planting cultivation when weeds are chemically conrolled.     

A Multi-Omics Characterization of the Natural Product Potential of Tropical Filamentous Marine Cyanobacteria

Microbial natural products are important for the understanding of microbial interactions, chemical defense and communication, and have also served as an inspirational source for numerous pharmaceutical drugs. Tropical marine cyanobacteria have been highlighted as a great source of new natural products, however, few reports have appeared wherein a multi-omics approach has been used to study their natural products potential (i.e., reports are often focused on an individual natural product and its biosynthesis). This study focuses on describing the natural product genetic potential as well as the expressed natural product molecules in benthic tropical cyanobacteria. We collected from several sites around the world and sequenced the genomes of 24 tropical filamentous marine cyanobacteria. The informatics program antiSMASH was used to annotate the major classes of gene clusters. BiG-SCAPE phylum-wide analysis revealed the most promising strains for natural product discovery among these cyanobacteria. LCMS/MS-based metabolomics highlighted the most abundant molecules and molecular classes among 10 of these marine cyanobacterial samples. We observed that despite many genes encoding for peptidic natural products, peptides were not as abundant as lipids and lipopeptides in the chemical extracts. Our results highlight a number of highly interesting biosynthetic gene clusters for genome mining among these cyanobacterial samples.     

Biomaterials and Bioactive Natural Products from Marine Invertebrates: From Basic Research to Innovative Applications

Aquatic invertebrates are a major source of biomaterials and bioactive natural products that can find applications as pharmaceutics, nutraceutics, cosmetics, antibiotics, antifouling products and biomaterials. Symbiotic microorganisms are often the real producers of many secondary metabolites initially isolated from marine invertebrates; however, a certain number of them are actually synthesized by the macro-organisms. In this review, we analysed the literature of the years 2010–2019 on natural products (bioactive molecules and biomaterials) from the main phyla of marine invertebrates explored so far, including sponges, cnidarians, molluscs, echinoderms and ascidians, and present relevant examples of natural products of interest to public and private stakeholders. We also describe omics tools that have been more relevant in identifying and understanding mechanisms and processes underlying the biosynthesis of secondary metabolites in marine invertebrates. Since there is increasing attention on finding new solutions for a sustainable large-scale supply of bioactive compounds, we propose that a possible improvement in the biodiscovery pipeline might also come from the study and utilization of aquatic invertebrate stem cells.     

Marine Power on Cancer: Drugs,Lead Compounds,and Mechanisms

Worldwide, 19.3 million new cancer cases and almost 10.0 million cancer deaths occur each year. Recently, much attention has been paid to the ocean, the largest biosphere of the earth that harbors a great many different organisms and natural products, to identify novel drugs and drug candidates to fight against malignant neoplasms. The marine compounds show potent anticancer activity in vitro and in vivo, and relatively few drugs have been approved by the U.S. Food and Drug Administration for the treatment of metastatic malignant lymphoma, breast cancer, or Hodgkin′s disease. This review provides a summary of the anticancer effects and mechanisms of action of selected marine compounds, including cytarabine, eribulin, marizomib, plitidepsin, trabectedin, zalypsis, adcetris, and OKI-179. The future development of anticancer marine drugs requires innovative biochemical biology approaches and introduction of novel therapeutic targets, as well as efficient isolation and synthesis of marine-derived natural compounds and derivatives.     

茶皂素在农药工业中应用研究进展

总结了茶皂素在农药工业领域中的应用概况 ,提出了今后开发的可能途径。文中对茶皂素在农药工业中应用的作用机理进行了论述 ,从茶皂素的表面张力、接触角和湿润性 ,证明茶皂素是一种适合农药工业应用的天然表面活性剂。实践证明 ,茶皂素作为可湿性粉型农药的湿润剂 ,能使可湿性粉剂农药的湿润性、pH、悬浮率等各项指标都能达到或超过国家规定标准。茶皂素在乳油型农药中应用 ,可以作为增效、展着剂 ,提高农药的施用效果。茶皂素在除草剂可溶粉、水剂方面应用能够提高产品质量和施用效果 ,总体水平优于国外同类产品。本文还对茶皂素作为生物农药在水产养殖作清池剂、作物和蔬菜种植业作杀虫剂、杀菌剂、灭螺剂等方面作了介绍     

我国抗ALS类除草剂油菜种质创制与研究进展

化学除草是控制田间草害的有效手段,但我国油菜化除面积非常有限。创制对特定除草剂具有选择抗性的油菜新种质,选育抗性品种是实现我国油菜化除的有效途径。乙酰乳酸合酶(acetolactate synthase,ALS) 类除草剂具有高效低量、选择性强、杀草谱广等优点,在生产上得到广泛应用。本文简述了ALS 基因及其突变产生抗性的机制,着重介绍我国基于ALS靶酶突变的抗除草剂油菜种质创制、抗性生理生化和分子机理等方面的研究进展,并探讨了抗除草剂新种质在油菜抗性新品种选育、杂交油菜制种及抗性基因在转基因工程中的应用。     

Marine Pharmacology in 2016–2017: Marine Compounds with Antibacterial,Antidiabetic, Antifungal,Anti-Inflammatory,Antiprotozoal, Antituberculosis and Antiviral Activities; Affecting the Immune and Nervous Systems,and Other Miscellaneous Mechanisms of Action

The review of the 2016–2017 marine pharmacology literature was prepared in a manner similar as the 10 prior reviews of this series. Preclinical marine pharmacology research during 2016–2017 assessed 313 marine compounds with novel pharmacology reported by a growing number of investigators from 54 countries. The peer-reviewed literature reported antibacterial, antifungal, antiprotozoal, antituberculosis, and antiviral activities for 123 marine natural products, 111 marine compounds with antidiabetic and anti-inflammatory activities as well as affecting the immune and nervous system, while in contrast 79 marine compounds displayed miscellaneous mechanisms of action which upon further investigation may contribute to several pharmacological classes. Therefore, in 2016–2017, the preclinical marine natural product pharmacology pipeline generated both novel pharmacology as well as potentially new lead compounds for the growing clinical marine pharmaceutical pipeline, and thus sustained with its contributions the global research for novel and effective therapeutic strategies for multiple disease categories.     

Antimicrobials from Seaweeds for Food Applications

The exponential growth of emerging multidrug-resistant microorganisms, including foodborne pathogens affecting the shelf-life and quality of foods, has recently increased the needs of the food industry to search for novel, natural and eco-friendly antimicrobial agents. Macroalgae are a bio-diverse group distributed worldwide, known to produce multiple compounds of diverse chemical nature, different to those produced by terrestrial plants. These novel compounds have shown promising health benefits when incorporated into foods, including antimicrobial properties. This review aims to provide an overview of the general methods and novel compounds with antimicrobial properties recently isolated and characterized from macroalgae, emphasizing the molecular pathways of their antimicrobial mechanisms of action. The current scientific evidence on the use of macroalgae or macroalgal extracts to increase the shelf-life of foods and prevent the development of foodborne pathogens in real food products and their influence on the sensory attributes of multiple foods (i.e., meat, dairy, beverages, fish and bakery products) will also be discussed, together with the main challenges and future trends of the use of marine natural products as antimicrobials.     

An overview of German cockroach, Blattella germanica, studies conducted in Iran

The control and elimination of German cockroach, the most important worldwide pest species, has been an economic and public health success. Too many studies have been conducted in Iran, whereas these researches was scattered in form of national and international articles that has needed to add up of them in an overview article. With doing of this work the way is smooth to future studies and the strategies of these studies will be distinguished. This article is outlook in direction of above aims. The susceptibility level and insecticide resistance mechanisms of German cockroach to organochlorated, organophosphate, carbamate and pyrethroid insecticide groups have been studied. The new insecticidal compounds include fipronil and avermectins acting at GABA and glutamate receptors in proximity to chloride channels, diacylhydrazines mimicking the action of ecdysone, indoxacarb acting at a novel site in sodium channels and imidacloprid, thiamethoxam and spinosad acting at novel sites on the nicotinic acetylcholine receptor, several promising products acting at new target sites, which are currently not affected by resistance that will be used for pest control specially Blattella germanica. Attentive to resistance of B. germanica to current consuming insecticides and ever-increasing add to intensity of it, the researchers have been considering the susceptibility level of B. germanica and efficiency estimation of them to above-mentioned insecticides for control of this pest. The strategies of future researches are study of the susceptibility level of B. germanica and efficiency estimation of them to above-mentioned insecticides for control of this pest in Iran.     

An Overview of Potential Seaweed-Derived Bioactive Compounds for Pharmaceutical Applications

Nowadays, seaweeds are widely involved in biotechnological applications. Due to the variety of bioactive compounds in their composition, species of phylum Ochrophyta, class Phaeophyceae, phylum Rhodophyta and Chlorophyta are valuable for the food, cosmetic, pharmaceutical and nutraceutical industries. Seaweeds have been consumed as whole food since ancient times and used to treat several diseases, even though the mechanisms of action were unknown. During the last decades, research has demonstrated that those unique compounds express beneficial properties for human health. Each compound has peculiar properties (e.g., antioxidant, antimicrobial, antiviral activities, etc.) that can be exploited to enhance human health. Seaweed’s extracted polysaccharides are already involved in the pharmaceutical industry, with the aim of replacing synthetic compounds with components of natural origin. This review aims at a better understanding of the recent uses of algae in drug development, with the scope of replacing synthetic compounds and the multiple biotechnological applications that make up seaweed’s potential in industrial companies. Further research is needed to better understand the mechanisms of action of seaweed’s compounds and to embrace the use of seaweeds in pharmaceutical companies and other applications, with the final scope being to produce sustainable and healthier products.     

Dithiolopyrrolone Natural Products: Isolation,Synthesis and Biosynthesis

Dithiolopyrrolones are a class of antibiotics that possess the unique pyrrolinonodithiole (4H-[1,2] dithiolo [4,3-b] pyrrol-5-one) skeleton linked to two variable acyl groups. To date, there are approximately 30 naturally occurring dithiolopyrrolone compounds, including holomycin, thiolutin, and aureothricin, and more recently thiomarinols, a unique class of hybrid marine bacterial natural products containing a dithiolopyrrolone framework linked by an amide bridge with an 8-hydroxyoctanoyl chain linked to a monic acid. Generally, dithiolopyrrolone antibiotics have broad-spectrum antibacterial activity against various microorganisms, including Gram-positive and Gram-negative bacteria, and even parasites. Holomycin appeared to be active against rifamycin-resistant bacteria and also inhibit the growth of the clinical pathogen methicillin-resistant Staphylococcus aureus N315. Its mode of action is believed to inhibit RNA synthesis although the exact mechanism has yet to be established in vitro. A recent work demonstrated that the fish pathogen Yersinia ruckeri employs an RNA methyltransferase for self-resistance during the holomycin production. Moreover, some dithiolopyrrolone derivatives have demonstrated promising antitumor activities. The biosynthetic gene clusters of holomycin have recently been identified in S. clavuligerus and characterized biochemically and genetically. The biosynthetic gene cluster of thiomarinol was also identified from the marine bacterium Pseudoalteromonas sp. SANK 73390, which was uniquely encoded by two independent pathways for pseudomonic acid and pyrrothine in a novel plasmid. The aim of this review is to give an overview about the isolations, characterizations, synthesis, biosynthesis, bioactivities and mode of action of this unique family of dithiolopyrrolone natural products, focusing on the period from 1940s until now.     

Interactions of fungicide-herbicide combinations against plant pathogens and weeds

The fungicide cyproconazole and four herbicides, DNOC, dicamba, ioxynil and bromoxynil, were tested singly and in mixtures against Rhizoctonia cerealis (in vitro and on wheat) and against Pseudocercosporella herpotrichoides (in vitro, as well as against two weeds, Avena fatua and Sinapis alba. Cyproconazole showed very strong fungicidal acitivity against both fungi. DNOC was inhibitory to the fungi in vitro but had little effect on the disease; dicamba had low activity against the fungi in vitro but prevented the disease on wheat. Ioxynol and bromoxynil were moderately fungitoxic both in vitro and against the disease. Cyproconazole-herbicide mixtures were synergistic in their action against both fungi in vitro and against the disease. The level of synergism depended on the relative proportion of fungicide and herbicide components in the mixtures. Mixtures of herbicides with cyproconazole against weeds were at best additive in their activity.