Induction of Secondary Metabolite Biosynthesis by Deleting the Histone Deacetylase HdaA in the Marine-Derived Fungus Aspergillus terreus RA2905

Undescribed alkaloids, peptides and polyketides from marine sediment-derived fungus Aspergillus terreus PPS1

The chemical investigation of the marine sediment-derived fungus Aspergillus terreus PPS1 led to the isolation and identification of seven previously undescribed secondary metabolites, including three alkaloids, asperspiroids A, B (1, 2) and astepyrazinol C (3), two lumazine peptides, terrelumamides C, D (5, 6), and two polyketides, scytalols E, F (8, 9), together with two known compounds. The structures of these undescribed compounds were elucidated by comprehensive spectroscopic analysis of NMR and HRESIMS data, and the absolute configurations were determined using ECD calculations, modified Mosher's method, and Marfey's analysis. Notably, asperspiroids A, B (1, 2) were uncommon alkaloids characterized by a rare 6/5/6 indole spirocyclolactone structure found naturally. The isolated compounds were assessed for their potential antibacterial, cytotoxic and anti-inflammatory activities. Astepyrazinol C (3) and its analog astepyrazinol B (4) demonstrated significant inhibition activity against LPS-induced NO production in RAW264.7 macrophages, with inhibition rates of 37.4% and 64.6%, respectively, at a concentration of 20 μM.

Discovery of Antibacterial Azaphilone Hybrid Metabolites from Marine-Derived Aspergillus terreus PPS1

Three novel azaphilone hybrids (1-3) with two types of structural units, along with four known compounds (4-7), were obtained from the marine sediment-derived fungus Aspergillus terreus PPS1. Asperbenzophilone A (1) features an unprecedented 6/6/6/6 ring system containing a hemiketal group. Butyropyranones I and II (2 and 3) are equipped with an azaphilone fragment preasperpyranone and a butyrolactone, which are connected through ether bonds. Comprehensive spectroscopic techniques, ECD calculations, and deduction of biosynthetic pathways were used to confirm the planar structures and absolute configurations of the new compounds. Compound 2 displayed significant anti-MRSA activity. Additionally, compound 2 exhibited moderate cytotoxic activity on human tumor cell lines 786-O, 5637, MCF-7, A-673, and 293T and medium inhibitory activity against the SARS-CoV-2 main protease (Mpro/3CLpro).

Asptertides A-H, C13-Polyketides From a Marine-Derived Aspergillus terreus

In the present study, 11 C13-polyketides comprising a monocyclic skeleton of an aromatic (1-6 and 11) or a cyclohexanone moiety (7) and an oxygenated bicyclic nucleus (8-10) were isolated from a mutated strain of endophytic fungus Aspergillus terreus RA2905. Five pairs of enantiomers (2a/b-5a/b and 7a/b) were achieved by chiral-phase HPLC separation. The structures of previously unreported asptertides A-H (1-8) were determined by analysis of the spectroscopic data and electronic circular dichroism (ECD) calculations. 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging bioassays revealed that some compounds showed moderate antioxidant effects, with IC50 values ranging from 13.7 to 35.6 µM.

Regulation of Histone Acetylation Modification on Biosynthesis of Secondary Metabolites in Fungi

The histone acetylation modification is a conservative post-translational epigenetic regulation in fungi. It includes acetylation and deacetylation at the lysine residues of histone, which are catalyzed by histone acetyltransferase (HAT) and deacetylase (HDAC), respectively. The histone acetylation modification plays crucial roles in fungal growth and development, environmental stress response, secondary metabolite (SM) biosynthesis, and pathogenicity. One of the most important roles is to regulate the gene expression that is responsible for SM biosynthesis in fungi. This mini-review summarized the regulation of histone acetylation modification by HATs and HDACs on the biosynthesis of SMs in fungi. In most cases, histone acetylation by HATs positively regulated the biosynthesis of fungal SMs, while HDACs had their negative regulations. Some HATs and HDACs were revealed to regulate fungal SM biosynthesis. Hda1 was found to be the most efficient regulator to affect the biosynthesis of SMs in fungi. The regulated fungal species were mainly from the genera of Aspergillus, Calcarisporium, Cladosporium, Fusarium, Monascus, Penicillium, and Pestalotiopsis. With the strategy of histone acetylation modification, the biosynthesis of some harmful SMs will be inhibited, while the production of useful bioactive SMs will be promoted in fungi. The subsequent research should focus on the study of regulatory mechanisms.

Pleiotropically activation of azaphilone biosynthesis by overexpressing a pathway-specific transcription factor in marine-derived Aspergillus terreus RA2905

The genome sequencing of Aspergillus terreus reveals that the vast number of predicted biosynthetic gene clusters have not reflected by the metabolic profile observed under conventional culture conditions. In this study, a silent azaphilone biosynthetic gene cluster was activated by overexpressing a pathway-specific transcription factor gene2642 in marine-derived fungus A. terreus RA2905. Consequently, twenty azaphilone compounds were identified from the OE2642 mutant, including 11 new azaphilones and their precursors, azasperones C-J (1-5, 7-9) and preazasperones A-C (15-17). The structures of those new compounds were unambiguously determined on the basis of NMR and HRESIMS spectra analysis, and the absolute configurations were established depending on ECD calculations. Compounds 1 and 2 were the rarely reported naturally occurring azaphilones with 2-N coupled phenyl-derivative. The bioactivity assay revealed that compounds 18-20 exhibited significant anti-inflammatory activity. Based on the occurrence of diverse intermediates and the putative gene functions, a plausible biosynthetic pathway of these compounds was proposed. The above results demonstrated that overexpression of the pathway-specific transcription factor presents a promising approach for enriching fungal secondary metabolites and accelerating the targeted discovery of novel biosynthetic products.

Epigenetic modifiers as inducer of bioactive secondary metabolites in fungi

Scientists are making efforts to search for new metabolites as they are essential lead molecules for the drug discovery, much required due to the evolution of multi drug resistance and new diseases. Moreover, higher production of known drugs is required because of the ever growing population. Microorganisms offer a vast collection of chemically distinct compounds that exhibit various biological functions. They play a crucial role in safeguarding crops, agriculture, and combating several infectious ailments and cancer. Research on fungi have grabbed a lot of attention after the discovery of penicillin, most of the compounds produced by fungi under normal cultivation conditions are discovered and now rarely new compounds are discovered. Treatment of fungi with the epigenetic modifiers has been becoming very popular since the last few years to boost the discovery of new molecules and enhance the production of already known molecules. Epigenetic literally means above genetics that actually does not alter the genome but alter its expression by altering the state of chromatin from heterochromatin to euchromatin. Chromatin in heterochromatin state usually doesn't express because it is closely packed by histones in this state. Epigenetic modifiers loosen the packing of chromatin by inhibiting DNA methylation and histone deacetylation and thus permit the expression of genes that usually remain dormant. This study delves into the possibility of utilizing epigenetic modifying agents to generate pharmacologically significant secondary metabolites from fungi.

Screening and genetic engineering of marine-derived Aspergillus terreus for high-efficient production of lovastatin

BACKGROUND

Lovastatin has widespread applications thanks to its multiple pharmacological effects. Fermentation by filamentous fungi represents the major way of lovastatin production. However, the current lovastatin productivity by fungal fermentation is limited and needs to be improved.

RESULTS

In this study, the lovastatin-producing strains of Aspergillus terreus from marine environment were screened, and their lovastatin productions were further improved by genetic engineering. Five strains of A. terreus were isolated from various marine environments. Their secondary metabolites were profiled by metabolomics analysis using Ultra Performance Liquid Chromatography-Mass spectrometry (UPLC-MS) with Global Natural Products Social Molecular Networking (GNPS), revealing that the production of secondary metabolites was variable among different strains. Remarkably, the strain of A. terreus MJ106 could principally biosynthesize the target drug lovastatin, which was confirmed by High Performance Liquid Chromatography (HPLC) and gene expression analysis. By one-factor experiment, lactose was found to be the best carbon source for A. terreus MJ106 to produce lovastatin. To improve the lovastatin titer in A. terreus MJ106, genetic engineering was applied to this strain. Firstly, a series of strong promoters was identified by transcriptomic and green fluorescent protein reporter analysis. Then, three selected strong promoters were used to overexpress the transcription factor gene lovE encoding the major transactivator for lov gene cluster expression. The results revealed that compared to A. terreus MJ106, all lovE over-expression mutants exhibited significantly more production of lovastatin and higher gene expression. One of them, LovE-b19, showed the highest lovastatin productivity at a titer of 1512 mg/L, which represents the highest production level reported in A. terreus.

CONCLUSION

Our data suggested that combination of strain screen and genetic engineering represents a powerful tool for improving the productivity of fungal secondary metabolites, which could be adopted for large-scale production of lovastatin in marine-derived A. terreus.

Marine Aspergillus: A Treasure Trove of Antimicrobial Compounds

Secondary metabolites from marine organisms are diverse in structure and function. Marine Aspergillus is an important source of bioactive natural products. We reviewed the structures and antimicrobial activities of compounds isolated from different marine Aspergillus over the past two years (January 2021-March 2023). Ninety-eight compounds derived from Aspergillus species were described. The chemical diversity and antimicrobial activities of these metabolites will provide a large number of promising lead compounds for the development of antimicrobial agents.

Marine Natural Products from the Beibu Gulf: Sources, Chemistry, and Bioactivities

Marine natural products (MNPs) play an important role in the discovery and development of new drugs. The Beibu Gulf of South China Sea harbors four representative marine ecosystems, including coral reefs, mangroves, seaweed beds, and coastal wetlands, which are rich in underexplored marine biological resources that produce a plethora of diversified MNPs. In our ongoing efforts to discover novel and biologically active MNPs from the Beibu Gulf, we provide a systematic overview of the sources, chemical structures, and bioactive properties of a total of 477 new MNPs derived from the Beibu Gulf, citing 133 references and covering the literature from the first report in November 2003 up to September 2022. These reviewed MNPs were structurally classified into polyketides (43%), terpenoids (40%), nitrogen-containing compounds (12%), and glucosides (5%), which mainly originated from microorganisms (52%) and macroorganisms (48%). Notably, they were predominantly found with cytotoxic, antibacterial, and anti-inflammatory activities. This review will shed light on these untapped Beibu Gulf-derived MNPs as promising lead compounds for the development of new drugs.