Current status of secondary metabolite pathways linked to their related biosynthetic gene clusters in Aspergillus section Nigri

Whole-genome sequencing of marine water-derived Curvularia verruculosa KHW-7: a pioneering study

Marine microorganisms are renowned for being a rich source of new secondary metabolites that are significant to humans. The fungi strain KHW-7 was isolated from the seawater collected from the Gulf of Khambhat, India, and identified as Curvularia verruculosa KHW-7. On a next-generation sequencing platform, C. verruculosa KHW-7's whole-genome sequencing (WGS) and gene annotation were carried out using several bioinformatic methods. The 31.59 MB genome size, 52.3% GC, and 158 bp mean read length were discovered using WGS. This genome also contained 9,745 protein-coding genes, including 852 secreted proteins and 2048 transmembrane proteins. The antiSMASH algorithm used to analyze genomes found 25 secondary metabolite biosynthetic gene clusters (BGCs) that are abundant in terpene, non-ribosomal peptide synthetase (NRPS), and polyketides type 1 (T1PKS). To our knowledge, this is the first whole-genome sequence report of C. verruculosa. The WGS analysis of C. verruculosa KHW-7 indicated that this marine-derived fungus could be an efficient generator of bioactive secondary metabolites and an important industrial enzyme, both of which demand further investigation and development.

Bioprospecting of Aspergillus sp. as a promising repository for anti-cancer agents: a comprehensive bibliometric investigation

Cancer remains a significant global health challenge, claiming nearly 10 million lives in 2020 according to the World Health Organization. In the quest for novel treatments, fungi, especially Aspergillus species, have emerged as a valuable source of bioactive compounds with promising anticancer properties. This study conducts a comprehensive bibliometric analysis to map the research landscape of Aspergillus in oncology, examining publications from 1982 to the present. We observed a marked increase in research activity starting in 2000, with a notable peak from 2005 onwards. The analysis identifies key contributors, including Mohamed GG, who has authored 15 papers with 322 citations, and El-Sayed Asa, with 14 papers and 264 citations. Leading countries in this research field include India, Egypt, and China, with King Saud University and Cairo University as the leading institutions. Prominent research themes identified are "endophyte," "green synthesis," "antimicrobial," "anti-cancer," and "biological activities," indicating a shift towards environmentally sustainable drug development. Our findings highlight the considerable potential of Aspergillus for developing new anticancer therapies and underscore the necessity for further research to harness these natural compounds for clinical use.

Global Map of Specialized Metabolites Encoded in Prokaryotic Plasmids

Plasmids are the main mobile elements responsible for horizontal gene transfer (HGT) in microorganisms. These replicons extend the metabolic spectrum of their host cells by carrying functional genes. However, it is still unknown to what extent plasmids carry biosynthetic gene clusters (BGCs) related to the production of secondary or specialized metabolites (SMs). Here, we analyzed 9,183 microbial plasmids to unveil their potential to produce SMs, finding a large diversity of cryptic BGCs in a few varieties of prokaryotic host taxa. Some of these plasmids harbored 15 or more BGCs, and many others were exclusively dedicated to mobilizing BGCs. We found an occurrence pattern of BGCs within groups of homologous plasmids shared by a common taxon, mainly in host-associated microbes (e.g., Rhizobiales, Enterobacteriaceae members). Our results add to the knowledge of the ecological functions and potential industrial uses of plasmids and shed light on the dynamics and evolution of SMs in prokaryotes. IMPORTANCE Plasmids are mobile DNA elements that can be shared among microbial cells, and they are useful for bringing to fruition some microbial ecological traits. However, it is not known to what extent plasmids harbor genes related to the production of specialized/secondary metabolites (SMs). In microbes, these metabolites are frequently useful for defense purposes, signaling, etc. In addition, these molecules usually have biotechnological and clinical applications. Here, we analyzed the content, dynamics, and evolution of genes related to the production of SMs in >9,000 microbial plasmids. Our results confirm that some plasmids act as a reservoir of SMs. We also found that some families of biosynthetic gene clusters are exclusively present in some groups of plasmids shared among closely related microbes. Host-associated bacteria (e.g., plant and human microbes) harbor the majority of specialized metabolites encoded in plasmids. These results provide new knowledge about microbial ecological traits and might enable the discovery of novel metabolites.

Aspergillus niger Fermentation Broth Promotes Maize Germination and Alleviates Low Phosphorus Stress

Aspergillus niger is a type of soil fungus with the ability to dissolve insoluble phosphate and secrete organic metabolites such as citric acid. However, whether cell-free Aspergillus niger fermentation broth (AFB) promotes maize growth and alleviates low-phosphorus stress has not been reported. In this study, we explored their relationship through a hydroponics system. The results indicated that either too low or too high concentrations of AFB may inhibit seed germination potential and germination rate. Under low phosphorus conditions, all physiological indexes (biomass, soluble sugar content, root length, etc.) increased after AFB was applied. A qRT-PCR analysis revealed that the expression of the EXPB4 and KRP1 genes, which are involved in root development, was upregulated, while the expression of the CAT2 and SOD9 genes, which are keys to the synthesis of antioxidant enzymes, was downregulated. The expression of LOX3, a key gene in lipid peroxidation, was down-regulated, consistent with changes in the corresponding enzyme activity. These results indicate that the application of AFB may alleviate the oxidative stress in maize seedlings, reduce the oxidative damage caused by low P stress, and enhance the resistance to low P stress in maize seedlings. In addition, it reveals the potential of A. niger to promote growth and provides new avenues for research on beneficial plant-fungal interactions.

A genetic tool to express long fungal biosynthetic genes

BACKGROUND

Secondary metabolites (SMs) from mushroom-forming fungi (Basidiomycota) and early diverging fungi (EDF) such as Mucoromycota are scarcely investigated. In many cases, production of SMs is induced by unknown stress factors or is accompanied by seasonable developmental changes on fungal morphology. Moreover, many of these fungi are considered as non-culturable under laboratory conditions which impedes investigation into SM. In the post-genomic era, numerous novel SM genes have been identified especially from EDF. As most of them encode multi-module enzymes, these genes are usually long which limits cloning and heterologous expression in traditional hosts.

RESULTS

An expression system in Aspergillus niger is presented that is suitable for the production of SMs from both Basidiomycota and EDF. The akuB gene was deleted in the expression host A. niger ATNT∆pyrG, resulting in a deficient nonhomologous end-joining repair mechanism which in turn facilitates the targeted gene deletion via homologous recombination. The ∆akuB mutant tLK01 served as a platform to integrate overlapping DNA fragments of long SM genes into the fwnA locus required for the black pigmentation of conidia. This enables an easy discrimination of correct transformants by screening the transformation plates for fawn-colored colonies. Expression of the gene of interest (GOI) is induced dose-dependently by addition of doxycycline and is enhanced by the dual TetON/terrein synthase promoter system (ATNT) from Aspergillus terreus. We show that the 8 kb polyketide synthase gene lpaA from the basidiomycete Laetiporus sulphureus is correctly assembled from five overlapping DNA fragments and laetiporic acids are produced. In a second approach, we expressed the yet uncharacterized > 20 kb nonribosomal peptide synthetase gene calA from the EDF Mortierella alpina. Gene expression and subsequent LC-MS/MS analysis of mycelial extracts revealed the production of the antimycobacterial compound calpinactam. This is the first report on the heterologous production of a full-length SM multidomain enzyme from EDF.

CONCLUSIONS

The system allows the assembly, targeted integration and expression of genes of > 20 kb size in A. niger in one single step. The system is suitable for evolutionary distantly related SM genes from both Basidiomycota and EDF. This uncovers new SM resources including genetically intractable or non-culturable fungi.

In silico comparative genomic analysis unravels a new candidate protein arsenal specifically associated with Fusarium oxysporum f. sp. albedinis pathogenesis

Fusarium oxysporum f. sp albedinis (Foa) is a devastating fungus of date palms. To unravel the genetic characteristics associated with its pathogenesis, the two available genomes of Foa 133 and Foa 9 were compared with 49 genomes of 29 other pathogenic formae speciales belonging to Fusarium oxysporum species complex (FOSC). Foa 133 and Foa 9 have genomes of 56.23 Mb and 65.56 Mb with 17460 and 19514 putative coding genes. Of these genes, 30% lack functional annotation with no similarity to characterized proteins. The remaining genes were involved in pathways essential to the fungi's life and their adaptation. Foa secretome analysis revealed that both Foa strains possess an expanded number of secreted effectors (3003 in Foa 133 and 2418 in Foa 9). Those include effectors encoded by Foa unique genes that are involved in Foa penetration (Egh16-like family), host defense mechanisms suppression (lysM family) and pathogen protection (cysteine-rich protein family). The accessory protein SIX6, which induces plant cell death, was also predicted in Foa. Further analysis of secreted CAZymes revealed an arsenal of enzymes involved in plant cell wall degradation. This arsenal includes an exclusively Foa-specific CAZyme (GH5-7). Transcription factors and membrane transporters (MFS) involved in fungicide efflux have been predicted in Foa, in addition to a variety of secondary metabolites. These comprise mycotoxins as well as chrysogin, the latter provides Foa with resistance against adverse environmental conditions. Our results revealed new Foa proteins that could be targeted in future research in order to manage Bayoud disease.

Total Heterologous Biosynthesis of Fungal Natural Products in Aspergillus nidulans

Fungal natural products comprise a wide range of bioactive compounds including important drugs and agrochemicals. Intriguingly, bioinformatic analyses of fungal genomes have revealed that fungi have the potential to produce significantly more natural products than what have been discovered so far. It has thus become widely accepted that most biosynthesis pathways of fungal natural products are silent or expressed at very low levels under laboratory cultivation conditions. To tap into this vast chemical reservoir, the reconstitution of entire biosynthetic pathways in genetically tractable fungal hosts (total heterologous biosynthesis) has become increasingly employed in recent years. This review summarizes total heterologous biosynthesis of fungal natural products accomplished before 2020 using Aspergillus nidulans as heterologous hosts. We review here Aspergillus transformation, A. nidulans hosts, shuttle vectors for episomal expression, and chromosomal integration expression. These tools, collectively, not only facilitate the discovery of cryptic natural products but can also be used to generate high-yield strains with clean metabolite backgrounds. In comparison with total synthesis, total heterologous biosynthesis offers a simplified strategy to construct complex molecules and holds potential for commercial application.