Larvicidal Effects of Fungal Meroterpenoids in the Control ofAedes aegypti L., the Main Vector of Dengue and Yellow Fever

Austin-Type Meroterpenoids from Fungi Reported in the Last Five Decades: A Review

Austin was first isolated as a novel polyisoprenoid mycotoxin from Aspergillus ustus in 1976. Subsequently, some new austin-type meroterpenoids (ATMTs) have been continually found. This review attempts to give a comprehensive summary of progress on the isolation, chemical structural features, biological activities, and fungal biodiversity of 104 novel ATMTs from 5 genera of terrestrial- and marine-derived fungi reported from October 1976 to January 2023. The genera of Penicillium and Aspergillus are the two dominant producers, producing 63.5% and 30.8% of ATMTs, respectively. Moreover, about 26.9% of ATMTs display various pronounced bioactivities, including insecticidal, anti-inflammatory, cytotoxicity, antibacterial, and PTP1B inhibitory activities. The chemical diversity and potential activities of these novel fungal ATMTs are reviewed for a better understanding, and a relevant summary focusing on the source fungi and their taxonomy is provided to shed light on the future development and research of austin-type meroterpenoids.

Anti-Insect Properties of Penicillium Secondary Metabolites

In connection with their widespread occurrence in diverse environments and ecosystems, fungi in the genus Penicillium are commonly found in association with insects. In addition to some cases possibly implying a mutualistic relationship, this symbiotic interaction has mainly been investigated to verify the entomopathogenic potential in light of its possible exploitation in ecofriendly strategies for pest control. This perspective relies on the assumption that entomopathogenicity is often mediated by fungal products and that Penicillium species are renowned producers of bioactive secondary metabolites. Indeed, a remarkable number of new compounds have been identified and characterized from these fungi in past decades, the properties and possible applications of which in insect pest management are reviewed in this paper.

Biological activities of meroterpenoids isolated from different sources

Meroterpenoids are natural products synthesized by unicellular organisms such as bacteria and multicellular organisms such as fungi, plants, and animals, including those of marine origin. Structurally, these compounds exhibit a wide diversity depending upon the origin and the biosynthetic pathway they emerge from. This diversity in structural features imparts a wide spectrum of biological activity to meroterpenoids. Based on the biosynthetic pathway of origin, these compounds are either polyketide-terpenoids or non-polyketide terpenoids. The recent surge of interest in meroterpenoids has led to a systematic screening of these compounds for many biological actions. Different meroterpenoids have been recorded for a broad range of operations, such as anti-cholinesterase, COX-2 inhibitory, anti-leishmanial, anti-diabetic, anti-oxidative, anti-inflammatory, anti-neoplastic, anti-bacterial, antimalarial, anti-viral, anti-obesity, and insecticidal activity. Meroterpenoids also possess inhibitory activity against the expression of nitric oxide, TNF- α, and other inflammatory mediators. These compounds also show renal protective, cardioprotective, and neuroprotective activities. The present review includes literature from 1999 to date and discusses 590 biologically active meroterpenoids, of which 231 are from fungal sources, 212 are from various species of plants, and 147 are from marine sources such as algae and sponges.

Deep-Sea Natural Products from Extreme Environments: Cold Seeps and Hydrothermal Vents

The deep sea has been proven to be a great treasure for structurally unique and biologically active natural products in the last two decades. Cold seeps and hydrothermal vents, as typical representatives of deep-sea extreme environments, have attracted more and more attention. This review mainly summarizes the natural products of marine animals, marine fungi, and marine bacteria derived from deep-sea cold seeps and hydrothermal vents as well as their biological activities. In general, there were 182 compounds reported, citing 132 references and covering the literature from the first report in 1984 up to March 2022. The sources of the compounds are represented by the genera Aspergillus sp., Penicillium sp., Streptomyces sp., and so on. It is worth mentioning that 90 of the 182 compounds are new and that almost 60% of the reported structures exhibited diverse bioactivities, which became attractive targets for relevant organic synthetic and biosynthetic studies.

The Penicillium brasilianum Histone Deacetylase Clr3 Regulates Secondary Metabolite Production and Tolerance to Oxidative Stress

Most of the biosynthetic gene clusters (BGCs) found in microbes are silent under standard laboratory cultivation conditions due to the lack of expression triggering stimuli, representing a considerable drawback in drug discovery. To access the full biosynthetic potential, studies towards the activation of cryptic BGCs are essential. Histone acetylation status is an important regulator of chromatin structure, which impacts cell physiology and the expression of BGCs. In this study, clr3, a gene encoding a histone deacetylase in Penicillium brasilianum LaBioMMi 136, is deleted and associated phenotypic and metabolic changes are evaluated. The results indicate reduced growth under oxidative stress conditions in the ∆clr3 strain, higher intracellular reactive oxygen species (ROS) levels, and a different transcriptional profile of 13 ROS-related genes of both strains under basal and ROS-induced conditions. Moreover, the production of 14 secondary metabolites, including austin-related meroterpenoids, brasiliamides, verruculogen, penicillic acid, and cyclodepsipeptides was evaluated in the ∆clr3 strain, most of them being reduced. Accordingly, the addition of epigenetic modulators responsible for HDAC inhibition into P. brasilianum’s growth media also culminated in the reduction in secondary metabolite production. The results suggest that Clr3 plays an essential role in secondary metabolite biosynthesis in P. brasilianum, thus offering new strategies for the regulation of natural product synthesis by assessing chromatin modification.

Austins-Type Meroterpenoids from a Mangrove-Derived Penicillium sp

Three unusual austins-type meroterpenoids penicianstinoids C-E (1-3) were obtained from the mangrove-derived fungus Penicillium sp. TGM112. The structures of 1-3 including absolute configurations were determined by detailed NMR, MS spectroscopic data, X-ray diffraction analysis, and calculated electronic circular dichroism data. Penicianstinoid C (1) was the first austins-type meroterpenoid with a unique 6/6/6/5 rearranged tetracyclic skeleton possessing two unusual spirocyclic moieties (2-oxaspiro[5.5]undeca-4,7-dien-3-one and 6-methylene-2-oxaspiro[4.5]decane-1,4-dione). Penicianstinoid D (2) was an unusual austins-type meroterpenoid with a 6/6/6/6 tetracyclic skeleton containing an octahydro-2H-chromen-2-one unit. Penicianstinoid E (3) possessed a 6/5/6/6/6/5 fused hexacyclic skeleton with an uncommon five-membered ether ring system. The plausible biosynthetic pathway of 1-3 is also proposed. Compounds 1 and 3 inhibited the growth of newly hatched Helicoverpa armigera Hubner larvae with IC₅₀ values of 100 and 200 μg/mL, respectively.

Structurally Diverse Meroterpenoids from a Marine-Derived Aspergillus sp. Fungus

Three new meroterpenoids, asperaustins A-C (1-3), and seven known analogues (4-10) were isolated from a marine-derived Aspergillus sp. fungus. The structures and absolute configurations of these new compounds were unequivocally determined by extensive spectroscopic analyses and single-crystal X-ray diffraction analyses. Asperaustin A (1) possesses an unusual spiro[4.5]deca-3,6-dien-2-one moiety with a unique 5/6/6/6/5 pentacyclic skeleton. The absolute configurations of austinoneol A (7) and precalidodehydroaustin (9) were determined by single-crystal X-ray diffraction analyses using Cu Kα radiation for the first time.

Natural meroterpenoids isolated from the plant pathogenic fungus Verticillium albo-atrum with noteworthy modification action against voltage-gated sodium channels of central neurons of Helicoverpa armigera

A new meroterpenoid, named acetoxydehydroaustin A (1) and the known meroterpenoid austin (2) were isolated from the plant pathogenic fungus Verticillium albo-atrum. Their structures were established based on general spectroscopic techniques and the relative configuration of compound 1 was determined by single-crystal X-ray diffraction analysis. We first investigated and identified their significant electrophysiological effects on the gating kinetics of voltage-gated sodium channels in central neurons acutely dissociated from Helicoverpa armigera using whole-cell patch clamp technique. Similar to the effects of pyrethroids on sodium late currents, both compounds produced concentration-dependent modification of sodium channels, prolonging the kinetics of channel inactivation to generate large persistent late currents during depolarization. However, different from the effects of tefluthrin and deltamethrin on sodium channels, two meroterpenoids did not induce tail currents during deactivation. Compounds 1 and 2 also caused depolarizing shifts in the voltage dependence of channel activation. The V_0.5 shifted about 5.02mV and 6.32mV in the depolarizing direction by 50μM 1 and 50μM 2. The V_0.5 of voltage-dependent inactivation shifted about 11.42mV and 11.62mV respectively in the hyperpolarizing direction by 50μM 1 and 100μM 2. In addition, they prolonged the time course of recovery from fast-inactivation for sodium channels. The effects of two compounds on the voltage-dependent gating substantially increased the size of sodium window currents. The overlapped area of window currents increased about 89.69% and 44.51% respectively by 10μM compound 1 and 10μM compound 2. These findings show that both compounds have effects on sodium channel activation, inactivation and window currents. The voltage-gated sodium channels in central neurons of H. armigera are the target sites of two meroterpenoid natural products.

Rewiring of the Austinoid Biosynthetic Pathway in Filamentous Fungi

Filamentous fungi produce numerous high-value natural products (NPs). The biosynthetic genes for NPs are normally clustered in the genome. A valuable NP class is represented by the insecticidal austinoids. We previously determined their biosynthesis in the fungus Aspergillus calidoustus. After further computational analysis looking into the austinoid gene clusters in two additional distantly related fungi, Aspergillus nidulans and Penicillium brasilianum, a rearrangement of the genes was observed that corresponded to the diverse austinoid derivatives produced by each strain. By advanced targeted combinatorial engineering using polycistronic expression of selected genes, we rewired the austinoid pathway in the fungus A. nidulans, which then produced certain compounds of interest under industrially favored conditions. This was possible by exploiting the presence of genes previously thought to be irrelevant. Our work shows that comparative analysis of genomes can be used to not only discover new gene clusters but unearth the hidden potential of known metabolic pathways.

Insights into Penicillium brasilianum Secondary Metabolism and Its Biotechnological Potential

Over the past few years Penicillium brasilianum has been isolated from many different environmental sources as soil isolates, plant endophytes and onion pathogen. All investigated strains share a great ability to produce bioactive secondary metabolites. Different authors have investigated this great capability and here we summarize the metabolic potential and the biological activities related to P. brasilianum’s metabolites with diverse structures. They include secondary metabolites of an alkaloid nature, i.e., 2,5-diketopiperazines, cyclodepsipeptides, meroterpenoids and polyketides. Penicillium brasilianum is also described as a great source of enzymes with biotechnological application potential, which is also highlighted in this review. Additionally, this review will focus on several aspects of Penicillium brasilianum and interesting genomic insights.

Discovery of an Extended Austinoid Biosynthetic Pathway in Aspergillus calidoustus

Filamentous fungi produce a wide range of natural products that are commonly used in various industrial contexts (e.g., pharmaceuticals and insecticides). Meroterpenoids are natural products of interest because of their various biological activities. Among the meroterpenoids, there is a group of insecticidal compounds known as the austinoids. These compounds have also been studied because of their intriguing spiro-lactone ring formation along with various modifications. Here, we present an extension of the original austinol/dehydroaustinol biosynthesis pathway from Aspergillus nidulans in the recently identified filamentous fungus Aspergillus calidoustus. Besides the discovery and elucidation of further derivatives, genome mining led to the discovery of new putative biosynthetic genes. The genes involved in the biosynthesis of later austinoid products were characterized, and among them was a second polyketide synthase gene in the A. calidoustus cluster that was unusual because it was a noninterative polyketide synthase producing a diketide. This diketide product was then loaded onto the austinoid backbone, resulting in a new insecticidal derivative, calidodehydroaustin.

Bioactive natural products derived from mangrove-associated microbes

This review summarizes new findings concerning the sources and characteristics of various natural products that can be extracted from mangrove-associated microbes over the past three years (January 2011–December 2013).

Antiviral isoindolone derivatives from an endophytic fungus Emericella sp. associated with Aegiceras corniculatum

Chemical investigation of the endophytic fungus Emericella sp. (HK-ZJ) isolated from the mangrove plant Aegiceras corniculatum led to isolation of six isoindolones derivatives termed as emerimidine A and B and emeriphenolicins A and D, and six previously reported compounds named aspernidine A and B, austin, austinol, dehydroaustin, and acetoxydehydroaustin, respectively. Their structures were elucidated on the basis of NMR spectroscopic evidence while the anti-influenza A viral (H₁N₁) activities of eight compounds were also evaluated using the cytopathic effect (CPE) inhibition assay.

Alterações ultraestruturais em larvas de Aedes aegypti submetidas ao diterpeno labdano, isolado de Copaifera reticulata (Leguminosae), e à uma fração rica em taninos de Magonia pubescens (Sapindaceae)

INTRODUÇÃO: Dengue é um importante problema de saúde pública, em vários países, e tem como principal vetor o Aedes aegypti, mosquito mais adaptado às áreas urbanizadas. Apresenta-se, pela primeira vez, as alterações ultraestruturais em larvas de 3º estádio, desse mosquito, causadas pelos larvicidas naturais, um diterpeno labdano, extraído de Copaifera reticulata, e uma fração rica em taninos catéquicos, extraída de Magonia pubescens, evidenciando o mecanismo de ação dessas substâncias. MÉTODOS: Os experimentos foram realizados com larvas de 3º estádio em solução de 0,9ppm, do diterpeno (3-β-acetoxylabdan-8(17)-13-dien-15-óico) e de 3,7ppm, da fração majoritária de tanino catéquico de massa molecular 864Da. Obtiveram-se as substâncias através de fracionamentos cromatográficos sucessivos, identificadas por ressonância magnética nuclear de hidrogênio e espectrometria de massas. As larvas que atingiram estado letárgico foram coletadas e dissecadas e seus tubos digestórios fixados, desidratados, emblocados e polimerizados. Cortes ultrafinos foram feitos e contrastados com acetato de uranila 3% e citrato de chumbo, posteriormente, levados ao microscópio eletrônico. RESULTADOS: As principais alterações ultraestruturais provocadas pelos diterpeno e tanino sobre larvas de Aedes aegypti foram vacuolização citoplasmática, desorganização e degeneração celular, mudança estrutural dos microvilos e deslocamento das células da lâmina basal. CONCLUSÕES: O diterpeno e a fração rica em taninos catéquicos provocaram a morte das larvas de Aedes aegypti através da destruição celular no intestino médio.