Cell wall active antifungal compounds produced by the marine fungus Hypoxylon oceanicum LL-15G256. II. Isolation and structure determination

Bioactive Lipodepsipeptides Produced by Bacteria and Fungi

Natural products are a vital source for agriculture, medicine, cosmetics and other fields. Lipodepsipeptides (LPDs) are a wide group of natural products distributed among living organisms such as bacteria, fungi, yeasts, virus, insects, plants and marine organisms. They are a group of compounds consisting of a lipid connected to a peptide, which are able to self-assemble into several different structures. They have shown different biological activities such as phytotoxic, antibiotic, antiviral, antiparasitic, antifungal, antibacterial, immunosuppressive, herbicidal, cytotoxic and hemolytic activities. Their biological activities seem to be due to their interactions with the plasma membrane (MP) because they are able to mimic the architecture of the native membranes interacting with their hydrophobic segment. LPDs also have surfactant properties. The review has been focused on the lipodepsipeptides isolated from fungal and bacterial sources, on their biological activity, on the structure–activity relationships of some selected LPD subgroups and on their potential application in agriculture and medicine. The chemical and biological characterization of lipodepsipeptides isolated in the last three decades and findings that resulted from SCI-FINDER research are reported. A critical evaluation of the most recent reviews dealing with the same argument has also been described.

Secondary metabolites from mangrove-associated fungi: source, chemistry and bioactivities

Covering 1989 to 2020The mangrove forests are a complex ecosystem occurring at tropical and subtropical intertidal estuarine zones and nourish a diverse group of microorganisms including fungi, actinomycetes, bacteria, cyanobacteria, algae, and protozoa. Among the mangrove microbial community, mangrove associated fungi, as the second-largest ecological group of the marine fungi, not only play an essential role in creating and maintaining this biosphere but also represent a rich source of structurally unique and diverse bioactive secondary metabolites, attracting significant attention of organic chemists and pharmacologists. This review summarizes the discovery relating to the source and characteristics of metabolic products isolated from mangrove-associated fungi over the past thirty years (1989-2020). Its emphasis included 1387 new metabolites from 451 papers, focusing on bioactivity and the unique chemical diversity of these natural products.

Mycotoxins Biocontrol Methods for Healthier Crops and Stored Products

Contamination of crops with phytopathogenic genera such as Fusarium, Aspergillus, Alternaria, and Penicillium usually results in mycotoxins in the stored crops or the final products (bread, beer, etc.). To reduce the damage and suppress the fungal growth, it is common to add antifungal substances during growth in the field or storage. Many of these antifungal substances are also harmful to human health and the reduction of their concentration would be of immense importance to food safety. Many eminent researchers are seeking a way to reduce the use of synthetic antifungal compounds and to implement more eco-friendly and healthier bioweapons against fungal proliferation and mycotoxin synthesis. This paper aims to address the recent advances in the effectiveness of biological antifungal compounds application against the aforementioned fungal genera and their species to enhance the protection of ecological and environmental systems involved in crop growing (water, soil, air) and to reduce fungicide contamination of food derived from these commodities.

New Peptaibiotics and a Cyclodepsipeptide from Ijuhya vitellina: Isolation, Identification, Cytotoxic and Nematicidal Activities

Fungal associations with nematodes have attracted scientific attention because of the need to develop new biocontrol agents. In this context, Ijuhya vitellina, an antagonistic fungus previously isolated from the plant parasitic cyst nematode Heterodera filipjevi, was selected to carry out an in-depth metabolomic study for its active metabolites. Herein, three new nonapeptide peptaibols with leucinostatin based sequences were isolated and identified by 1, 2D NMR, and HR-ESI-MS-MS. The absolute configuration was assigned based on Marfay’s analysis and Mosher ester formation. The new leucinostatins manifested moderate nematicidal effect against the plant pathogenic nematode Pratylenchus penetrans with LD₉₀ values ranging from 5 to 7 µg/mL. Furthermore, a cyclodepsipeptide, named arthrichitin D, with five amino acid residues attached to a 3-hydroxy-2,4-dimethylhexadeca-4,6-dienoic fatty acid chain was discovered and showed weak nematicidal effect against Caenorhabditis elegans. Chaetoglobosin B and its 19-O-acetyl derivative were also obtained as minor metabolites, and the activity of chaetoglobosin B on the actin cytoskeleton of mammalian cells was assessed.

Marine Macrolides with Antibacterial and/or Antifungal Activity

Currently, the increasing resistance of microorganisms to antibiotics is a serious problem. Marine organisms are the source of thousands of substances, which also have antibacterial and antifungal effects. Among them, marine macrolides are significant. In this review, the antibacterial and/or antifungal activities of 34 groups of marine macrolides are presented. Exemplary groups are chalcomycins, curvulides, halichondramides, lobophorins, macrolactins, modiolides, scytophycins, spongistatins, or zearalanones. In the paper, 74 antibiotics or their analog sets, among which 29 with antifungal activity, 25 that are antibacterial, and 20 that are both antifungal and antibacterial are summarized. Also, 36 macrolides or their sets are produced by bacteria, 18 by fungi, ten by sponges, seven by algae, two by porifera, and one by nudibranch. Moreover, the chemical structures of representatives from each of the 34 groups of these antibiotics are presented. To summarize, marine organisms are rich in natural macrolides. Some of these may be used in the future in the treatment of bacterial and fungal infections. Marine macrolides can also be potential drugs applicable against pathogens resistant to currently known antibiotics.

Nematicidal Cyclic Lipodepsipeptides and a Xanthocillin Derivative from a Phaeosphariaceous Fungus Parasitizing Eggs of the Plant Parasitic Nematode Heterodera filipjevi

The new cyclic lipodepsipeptide ophiotine (1), two new arthrichitin derivatives named arthrichitins B (4) and C (5), a new xanthocillin-like alkaloid, xanthomide Z (2), and the previously described arthrichitin (3) were isolated from the liquid culture broth of a nematode-associated fungus with affinities to the genus Ophiosphaerella. The structural elucidation and determination of the absolute configuration of the new molecules were accomplished using a combination of spectroscopic and chemical techniques, including 1D and 2D NMR, HRMS, and Marfey's analysis. Opiotine (1) displayed moderate nematicidal activity against the host nematode ( Heterodera filipjevi), while xanthomide Z (2) exhibited very weak activity. Arthrichitin C (5) showed very weak cytotoxic effects on several cancer cell lines, with IC₅₀ values in the range of 24-33 μM. Xanthomide Z is among few xanthocillin derivatives that comprise formamide functions instead of the cyano functions that are usually observed in this class of fungal alkaloids.

Structural Diversity and Biological Activities of Cyclic Depsipeptides from Fungi

Cyclic depsipeptides (CDPs) are cyclopeptides in which amide groups are replaced by corresponding lactone bonds due to the presence of a hydroxylated carboxylic acid in the peptide structure. These peptides sometimes display additional chemical modifications, including unusual amino acid residues in their structures. This review highlights the occurrence, structures and biological activities of the fungal CDPs reported until October 2017. About 352 fungal CDPs belonging to the groups of cyclic tri-, tetra-, penta-, hexa-, hepta-, octa-, nona-, deca-, and tridecadepsipeptides have been isolated from fungi. These metabolites are mainly reported from the genera Acremonium, Alternaria, Aspergillus, Beauveria, Fusarium, Isaria, Metarhizium, Penicillium, and Rosellina. They are known to exhibit various biological activities such as cytotoxic, phytotoxic, antimicrobial, antiviral, anthelmintic, insecticidal, antimalarial, antitumoral and enzyme-inhibitory activities. Some CDPs (i.e., PF1022A, enniatins and destruxins) have been applied as pharmaceuticals and agrochemicals.

Evolution of Chemical Diversity in Echinocandin Lipopeptide Antifungal Metabolites

The echinocandins are a class of antifungal drugs that includes caspofungin, micafungin, and anidulafungin. Gene clusters encoding most of the structural complexity of the echinocandins provided a framework for hypotheses about the evolutionary history and chemical logic of echinocandin biosynthesis. Gene orthologs among echinocandin-producing fungi were identified. Pathway genes, including the nonribosomal peptide synthetases (NRPSs), were analyzed phylogenetically to address the hypothesis that these pathways represent descent from a common ancestor. The clusters share cooperative gene contents and linkages among the different strains. Individual pathway genes analyzed in the context of similar genes formed unique echinocandin-exclusive phylogenetic lineages. The echinocandin NRPSs, along with the NRPS from the inp gene cluster in Aspergillus nidulans and its orthologs, comprise a novel lineage among fungal NRPSs. NRPS adenylation domains from different species exhibited a one-to-one correspondence between modules and amino acid specificity that is consistent with models of tandem duplication and subfunctionalization. Pathway gene trees and Ascomycota phylogenies are congruent and consistent with the hypothesis that the echinocandin gene clusters have a common origin. The disjunct Eurotiomycete-Leotiomycete distribution appears to be consistent with a scenario of vertical descent accompanied by incomplete lineage sorting and loss of the clusters from most lineages of the Ascomycota. We present evidence for a single evolutionary origin of the echinocandin family of gene clusters and a progression of structural diversification in two fungal classes that diverged approximately 290 to 390 million years ago. Lineage-specific gene cluster evolution driven by selection of new chemotypes contributed to diversification of the molecular functionalities.

An assessment of natural product discovery from marine (sensu strictu) and marine-derived fungi

The natural products community has been investigating secondary metabolites from marine fungi for several decades, but when one attempts to search for validated reports of new natural products from marine fungi, one encounters a literature saturated with reports from ‘marine-derived’ fungi. Of the 1000+ metabolites that have been characterized to date, only approximately 80 of these have been isolated from species from exclusively marine lineages. These metabolites are summarized here along with the lifestyle and habitats of their producing organisms. Furthermore, we address some of the reasons for the apparent disconnect between the stated objectives of discovering new chemistry from marine organisms and the apparent neglect of the truly exceptional obligate marine fungi. We also offer suggestions on how to reinvigorate enthusiasm for marine natural products discovery from fungi from exclusive marine lineages and highlight the need for critically assessing the role of apparently terrestrial fungi in the marine environment.

Filamentous fungi from the Atlantic marine sponge Dragmacidon reticulatum

Dragmacidon reticulatum is a marine sponge of wide occurrence in the Eastern and Western Atlantic. Little is known about D. reticulatum fungal diversity. Filamentous fungi recovered from D. reticulatum were assessed in the present study using a polyphasic taxonomic approach, including classical morphology, molecular biology and MALDI-TOF ICMS. Ninety-eight fungal strains were isolated from two D. reticulatum samples by using six different culture media, which were identified up to the genus level. Sixty-four distinct fungal ribotypes were obtained, distributed among twenty-four different genera belonging to the Ascomycota and Zygomycota. Representatives of Penicillium and Trichoderma were the most diverse and abundant fungi isolated. Amongst Penicillium spp. three isolates belonged to the same ribotype can be considered as a putative new species. Data derived from the present study highlight the importance of using a polyphasic approach to get an accurate identification in order to structure a reliable culture collection.

Biotechnology of marine fungi

Filamentous fungi are the most widely used eukaryotes in industrial and pharmaceutical applications. Their biotechnological uses include the production of enzymes, vitamins, polysaccharides, pigments, lipids and others. Marine fungi are a still relatively unexplored group in biotechnology. Taxonomic and habitat diversity form the basis for exploration of marine fungal biotechnology. This review covers what is known of the potential applications of obligate and marine-derived fungi obtained from coastal to the oceanic and shallow water to the deep-sea habitats. Recent studies indicate that marine fungi are potential candidates for novel enzymes, bioremediation, biosurfactants, polysaccharides, polyunsaturated fatty acids and secondary metabolites. Future studies that focus on culturing rare and novel marine fungi, combined with knowledge of their physiology and biochemistry will provide a firm basis for marine mycotechnology.

A cell wall-active lipopeptide from the fungus Pochonia bulbillosa

Bioassay-directed fractionation of a fermentation of Pochonia bulbinosa, culture 38G272, led to the isolation of a series of structurally novel, prospective cell wall-active lipopeptides. The main component of this suite is 1, a linear hexapeptide with a delta-hydroxymyristic acid amide substituted N-terminus. The structure was deduced using high-field microsample NMR, Fourier transform mass spectrometry, and microscale chemical degradation. The potent cell wall activity and synthetically accessible structure of 1 make it a potential lead for further investigation.

Induced production of emericellamides A and B from the marine-derived fungus Emericella sp. in competing co-culture

Induction of the production of emericellamides A and B (1, 2), by the marine-derived fungus Emericella sp., was observed during co-culture with the marine actinomycete Salinispora arenicola. The planar structures of these new cyclic depsipeptides, which incorporate 3-hydroxy-2,4-dimethyldecanoic acid and 3-hydroxy-2,4,6-trimethyldodecanoic acid, were assigned by combined chemical and spectral methods. The absolute configurations of the amino acids, and those of the chiral centers on the side chain, were established by application of the Marfey's method, by J-based configuration analysis, and by application of the modified Mosher method. Emericellamides A and B show modest antibacterial activities against methicillin-resistant Staphylococcus aureus with MIC values of 3.8 and 6.0 microM, respectively.

Isolation and identification of the icosalides--cyclic peptolides with selective antibiotic and cytotoxic activities

Three cyclic peptolides have been isolated from two different fungal species and their structures determined. Icosalides A1 (1a), A2 (1b), and B (1c) each contain two serine and two leucine amino acid residues and incorporate two fatty acid moieties as part of the central twenty-member ring. 1a contains L-serine and both D- and L-leucine residues, while 1b and 1c contain only L-amino acid residues. Icosalide A1 displays antimicrobial activity against Streptococcus pyogenes, S. pneumoniae (Felton), and Enterococcus faecalis. Icosalides A2 and B are cytotoxic to replicating MDCK cells.

A chemical study of cyclic depsipeptides produced by a sponge-derived fungus

Two novel cyclic depsipeptides, guangomides A (1) and B (2), together with a new destruxin derivative (3) were isolated from the cytotoxic extract obtained from the saltwater culture of an unidentifiable sponge-derived fungus. The new structures were elucidated on the basis of analysis of extensive 1D and 2D NMR data sets, and the absolute configurations of 2S, 9S, 13S, 19S, 24R, 28R of 1 were determined on the basis of the combined X-ray and Marfey's method structure analysis. Identical absolute configurations were assumed for 2. The cytotoxicity of the extract was found to be due to brefeldin A, while 1 and 2 showed weak antibacterial activity against Staphylococcus epidermidis and Enterococcus durans.

Screening for new metabolites from marine microorganisms

This article gives an overview of current analysis techniques for the screening and the activity analysis of metabolites from marine (micro)organisms. The sequencing of marine genomes and the techniques of functional genomics (including transcriptome, proteome, and metabolome analyses) open up new possibilities for the screening of new metabolites of biotechnological interest. Although the sequencing of microbial marine genomes has been somewhat limited to date, selected genome sequences of marine bacteria and algae have already been published. This report summarizes the application of the techniques of functional genomics, such as transcriptome analysis in combination with high-resolution two-dimensional polyacrylamide gelelectrophoresis and mass spectrometry, for the screening for bioactive compounds of marine microorganisms. Furthermore, the target analysis of antimicrobial compounds by proteome or transcriptome analysis of bacterial model systems is described. Recent high-throughput screening techniques are explained. Finally, new approaches for the screening of metabolites from marine microorganisms are discussed.

Bioprocess Engineering Data on the Cultivation of Marine Prokaryotes and Fungi

The temperature/pressure dependency of marine prokaryotes and fungi, in terms of their growth behaviour as well as their potential to produce new metabolites or enzymes, is evaluated. Advanced shake-flask cultivations and controlled bioreactor cultivations following the batch-type, fed-batch-type and/or continuous-type procedures are summarized. After a summary of the fermentation data available so far, values on maximal biomass, specific growth rates, and (sub)optimal production yields are presented. The application of mesophilic microbes, especially bioactive metabolites, to intensify bioprocess engineering studies, is the goal. Cold-active enzymes and thermostable enzymes are the targets of experiments with psychrophilic and hyperthermophilic enzymes. A special challenge to bioengineers is also provided by barophilic strains originating from depths of, say, nearly 11000 m, or from hydrothermal vents.

Microbial natural products as a source of antifungals

The vast number and variety of chemotherapeutic agents isolated from microbial natural products and used to treat bacterial infections have greatly contributed to the improvement of human health during the past century. However, only a limited number of antifungal agents (polyenes and azoles, plus the recently introduced caspofungin acetate) are currently available for the treatment of life-threatening fungal infections. Furthermore, the prevalence of systemic fungal infections has increased significantly during the past decade. For this reason, the development of new antifungal agents, preferably with novel mechanisms of action, is an urgent medical need. A selection of antifungal agents in early stages of development, produced by micro-organisms, is summarized in this review. The compounds are classified according to their mechanisms of action, covering inhibitors of the synthesis of cell wall components (glucan, chitin and mannoproteins), of sphingolipid synthesis (serine palmitoyltransferase, ceramide synthase, inositol phosphoceramide synthase and fatty acid elongation) and of protein synthesis (sordarins). In addition, some considerations related to the chemotaxonomy of the producing organisms and some issues relevant to antifungal drug discovery are also discussed.

Integrated approach to explore the potential of marine microorganisms for the production of bioactive metabolites

During the last 10 years marine organisms have provided a large number of new natural products. Interesting compounds have mainly been derived from macroorganisms such as sponges, ascidians, corals and bryozoans. The number of secondary metabolites from marine microorganisms is smaller, but rapidly increasing. Because of the enormous difficulties involved in harvesting products from marine animals, and the fact that some of the bioactive compounds are produced by associated bacteria, the advantages of sustainable production of bioactive metabolites by bacteria or fungi, under the protection of natural resources, seem to be very attractive for the future. This review describes current progress in the isolation and identification of novel marine microorganisms, the discovery of new secondary metabolites, the biotechnological approaches to overproduce them, as well as the evaluation and characterization of their bioactivity.

Emerging novel antifungal agents

Promising new compounds have recently been identified in an effort to supplement the relatively sparse portfolio of antifungal drugs. Many of these compounds have defined mechanisms of action against fungal cells and have, in some cases, aided the identification of new selective targets in fungi. For most of these compounds, however, factors such as a narrow spectrum of activity, susceptibility to efflux pumps, protein binding, serum inactivation and poor pharmaceutical properties prevent their use in the clinic. Even so, these compounds are novel substrates for synthetic modifications that could lead to the discovery of future antifungal drugs.

Detection, synthesis, structure, and function of oligo(3-hydroxyalkanoates): contributions by synthetic organic chemists

Two types of the biological macromolecules poly(R-3-hydroxyalkanoates) have been identified: the high-molecular-weight microbial storage material (sPHA) and a short-chain variety, consisting of butyrate and valerate residues, complexed with other biomacromolecules such as calcium polyphosphate or proteins (cPHB/PHV). While sPHA has attracted, and still enjoys, a lot of attention from numerous scientists around the world, research on cPHB and the structurally and functionally related polymalate (PMA) is still in its infancy. In this article, we present a review on the chemical synthesis, structure, function and interactions of monodisperse cPHAs, the oligo(3-hydroxyalkanoates), with emphasis on the butyrates (OHB); we report hitherto unpublished results on the enzymatic degradation of cPHB and PMA, on a new analytical method for HB/HV detection in biological samples, and on OHB-mediated Ca2+ transport through phospholipid bilayers of artificial vesicles; finally, we discuss possible mechanisms of ion transport through cell membranes, as caused by cPHB. The speculative--and provocative--question is asked whether the structurally simple PHAs may have evolved as storage materials and amphiphilic macromolecules before poly-peptides, -saccharides, and -nucleic acids, in the history of life, or under prebiotic conditions.