Aspernidine A and B, prenylated isoindolinone alkaloids from the model fungus Aspergillus nidulans

Abstract

Filamentous fungi produce a multitude of bioactive natural products, which cover a broad range of useful pharmaceutical activities. Many of these compounds were discovered by traditional natural product screening approaches and have found various applications in modern medicine. 1,2 Through recent whole-genome sequencing projects, however, we become increasingly aware that the biosynthetic potential of microorganisms is much higher than expected. 3 In many cases, the number of putative biosynthetic genes of fungi and bacteria is not reflected by the metabolic profile observed under laboratory culture conditions. Several gene loci encoding diverse metabolic pathways seem to lack expression in the absence of particular physical or chemical stimuli. 4 Mining the genome of Aspergillus nidulans for putative biosynthesis gene clusters revealed biosynthetic abilities for the production of up to 28 polyketides and 24 nonribosomally synthesized peptides. 5,6 However, this abundance of gene clusters clearly outnumbers the known secondary metabolites of this fungus. To gain access to this untapped reservoir of potentially bioactive natural products, various strategies to induce the expression of silent genes have been developed. 4,7 Important recent examples involve the ectopic expression of a regulatory gene, 8 the induction of a transcription activator by promotor exchange, 9 as well as modulation of the epigenetic regulation of biosynthetic genes at the chromatin level. [10][11][12][13] Furthermore, it was shown that the intimate contact between A. nidulans and a soil-dwelling actinomycete may lead to the specific induction of a cryptic polyketide gene cluster. 14 These strategies resulted in the discovery of a set of novel secondary metabolites, which could not be located by classical screening methods. Another option often preceding genomic approaches is the systematic investigation of the microbial secondary metabolome under various growth conditions. Since the early days of fermentations, it is known that the choice of the cultivation parameters is critical to the number and type of secondary metabolites produced by microorganisms. 4 Thus, the formation of cryptic natural products can up to a certain extent be triggered by a systematic variation of standard fermentation parameters to increase the number of secondary compounds produced in the bacterial or fungal culture. 15,16 On the basis of the assumption that changing environmental conditions can shift the metabolic profile of an organism, we systematically varied the cultivation parameters to reinvestigate the metabolome of A. nidulans. In this study, we report the discovery of two new isoindole alkaloids, aspernidine A (1) and B (2), as an addition to the metabolic data of this important model fungus (Figure 1a). An A. nidulans extract library was prepared by adjusting 45 different culture conditions (variation of culture media, cultivation period, temperature and oxygen supply) and the metabolic profiles were screened by HPLC-DAD-MS. Investigation of the cultur...

Fungal Chemotaxonomy

“…However, this concept that one strain can produce many different compounds was already introduced in 1983 by Frisvad and Filtenborg for Penicillium species, where it was shown that the species examined had specific profiles of secondary metabolites, backed up by examining a large number of isolates of each species [31]. Furthermore, they used more than one medium for production of the different secondary metabolites to get the broadest possible profile, a concept also later recommended by Bode et al [121], Bills et al [122], Scherlach et al [123], Kjer et al [124], Nielsen et al [125], Tormo et al [126], and Frisvad [127,128]. Media that has been very useful for screening filamentous fungi have included yeast extract sucrose (YES) agar, Czapek yeast autolysate (CYA) agar, malt extract agar, and oat meal agar.…”

Natural Products Remain an Important Source for Drug Development in the Post-Genomic Era

“…It was shown that if the producing host was grown under alternative physicochemical conditions compared with the standard laboratory growth conditions, it will possess the ability to express the originally silent gene clusters. [13][14][15] Co-cultivation of microorganisms and the application of iChip (isolation chip) have also been proved to be successful in activating the silent gene cluster.…”

“…It was shown that if the producing host was grown under alternative physicochemical conditions compared with the standard laboratory growth conditions, it will possess the ability to express the originally silent gene clusters. [13][14][15] Co-cultivation of microorganisms and the application of iChip (isolation chip) have also been proved to be successful in activating the silent gene cluster. 16 Genomics-driven approaches 17 including mainly genome editing and genome engineering technologies by means of genetic manipulation of the target genome is believed to the most efficient but challenging and time-consuming methods to activate the silent or weakly-expressed gene clusters.…”

“…It was shown that if the producing host was grown under alternative physicochemical conditions compared with the standard laboratory growth conditions, it will possess the ability to express the originally silent gene clusters. [13][14][15] Co-cultivation of microorganisms and the application of iChip (isolation chip) have also been proved to be successful in activating the silent gene cluster.16 Genomics-driven approaches 17 including mainly genome editing and genome engineering technologies by means of genetic manipulation of the target genome is believed to the most efficient but challenging and time-consuming methods to activate the silent or weakly-expressed gene clusters. Researchers have proposed and verified different strategies in this field, such as heterologous expression of BGCs in heterologous hosts functionally, 18 manipulation of global and pathway-specific transcriptional regulators(and/or RNA polymerase or ribosomal proteins), 19 perturbation of epigenetic control(DNA/his tone methylation and acetylation).…”

Indole alkaloids from marine-derived fungus Aspergillus sydowii SCSIO 00305

“…1,2 The genus Aspergillus (Moniliaceae), with over 180 species, has attracted considerable attention as a rich source of alkaloids, terpenoids, xanthones, polyketides and etc, some of which showed antifungal, antibacterial, anti-HIV and cytotoxic activities. [3][4][5] In order to obtain new bioactive metabolites from marine fungi, we investigated on the marine fungal strain Aspergillus sydowii SCSIO 00305 isolated from a healthy tissue of Verrucella umbraculum. Bioassay-guided fractionation led to the isolation of a new indole diketopiperazine alkaloid, cyclotryprostatin E (1), together with nine known ones, [4-(2-methoxyphenyl)-1-piperazinyl][(1-methyl-1H-indol-3-yl)]-methanone (2), cyclotryprostatin B (3), 6 fumiquinazoline D (4), 7 fumitremorgin B (5), 8 fumiquinazoline C (6), 7 fumiquinazoline B (7), 7 fumiquinazoline A (8), 7 fumiquinazoline F (9), 7 fumiquinazoline G (10) 7 from a culture broth of the strain.…”