Improvement of Aspergillus nidulans penicillin production by targeting AcvA to peroxisomes

Enhanced precision and efficiency in metabolic regulation: Compartmentalized metabolic engineering

Metabolic engineering has witnessed remarkable advancements, enabling successful large-scale, cost-effective and efficient production of numerous compounds. However, the predominant expression of heterologous genes in the cytoplasm poses limitations, such as low substrate concentration, metabolic competition and product toxicity. To overcome these challenges, compartmentalized metabolic engineering allows the spatial separation of metabolic pathways for the efficient and precise production of target compounds. Compartmentalized metabolic engineering and its common strategies are comprehensively described in this study, where various membranous compartments and membraneless compartments have been used for compartmentalization and constructive progress has been made. Additionally, the challenges and future directions are discussed in depth. This review is dedicated to providing compartmentalized, precise and efficient methods for metabolic production, and provides valuable guidance for further development in the field of metabolic engineering.

Exploring the Subcellular Localization of Monascus Pigments Biosynthases: Preliminary Unraveling of the Compartmentalization Mechanism

Monascus pigments (MPs), a class of secondary metabolites produced by Monascus spp., can be classified into yellow, orange, and red MPs according to their differences in the wavelength of the maximum absorption. However, the biosynthetic sequence and cellular biosynthesis mechanism of different MPs components are still not yet completely clear in Monascus spp. In this study, the subcellular localization of five MPs synthases was investigated using fluorescent protein fusion expression. The results revealed that the proteins encoded by the MPs biosynthetic gene cluster were compartmentalized in various subcellular locations, including the mitochondrial polyketide synthase MrPigA, cytosolic enzymes consisting of the ketoreductase MrPigC, the oxidoreductase MrPigE, and the monooxygenase MrPigN, and the cell-wall-bound oxidoreductase MrPigF. Moreover, the correct localization of MrPigF to the cell wall was crucial for the synthesis of orange MPs. Lastly, we discussed the compartmentalized biosynthetic pathway of MPs. This study will not only be helpful in clarifying the biosynthetic sequence and biosynthesis mechanism of different MPs but also provides new insights into the cellular biosynthesis of secondary metabolites in filamentous fungi.

The spatial organization of sphingofungin biosynthesis in Aspergillus fumigatus and its cross-interaction with sphingolipid metabolism

Sphingofungins are sphinganine analog mycotoxins acting as inhibitors of serine palmitoyl transferases, enzymes responsible for the first step in the sphingolipid biosynthesis. Eukaryotic cells are highly organized with various structures and organelles to facilitate cellular processes and chemical reactions, including the ones occurring as part of the secondary metabolism. We studied how sphingofungin biosynthesis is compartmentalized in the human-pathogenic fungus Aspergillus fumigatus, and we observed that it takes place in the endoplasmic reticulum (ER), ER-derived vesicles, and the cytosol. This implies that sphingofungin and sphingolipid biosynthesis colocalize to some extent. Automated analysis of confocal microscopy images confirmed the colocalization of the fluorescent proteins. Moreover, we demonstrated that the cluster-associated aminotransferase (SphA) and 3-ketoreductase (SphF) play a bifunctional role, supporting sphingolipid biosynthesis, and thereby antagonizing the toxic effects caused by sphingofungin production.IMPORTANCEA balanced sphingolipid homeostasis is critical for the proper functioning of eukaryotic cells. To this end, sphingolipid inhibitors have therapeutic potential against diseases related to the deregulation of sphingolipid balance. In addition, some of them have significant antifungal activity, suggesting that sphingolipid inhibitors-producing fungi have evolved mechanisms to escape self-poisoning. Here, we propose a novel self-defense mechanism, with cluster-associated genes coding for enzymes that play a dual role, being involved in both sphingofungin and sphingolipid production.

Peroxisome-based metabolic engineering for biomanufacturing and agriculture

Subcellular compartmentalization of metabolic pathways plays a crucial role in metabolic engineering. The peroxisome has emerged as a highly valuable and promising compartment for organelle engineering, particularly in the fields of biological manufacturing and agriculture. In this review, we summarize the remarkable achievements in peroxisome engineering in yeast, the industrially popular biomanufacturing chassis host, to produce various biocompounds. We also review progress in plant peroxisome engineering, a field that has already exhibited high potential in both biomanufacturing and agriculture. Moreover, we outline various experimentally validated strategies to improve the efficiency of engineered pathways in peroxisomes, as well as prospects of peroxisome engineering.

How to improve the production of peptidyl compounds in filamentous fungi

Peptidyl compounds produced by filamentous fungi, which are nonribosomal peptides (NRPs) and ribosomally synthesized and post-translationally modified peptides (RiPPs), are rich sources of bioactive compounds with a wide variety of structures. Some of these peptidyl compounds are useful as pharmaceuticals and pesticides. However, for industrial use, their low production often becomes an obstacle, and various approaches have been challenged to overcome this weakness. In this article, we summarize the successful attempts to increase the production of NRPs and RiPPs in filamentous fungi and present our perspectives on how to improve it further.

Biosynthetic process and strain improvement approaches for industrial penicillin production

Penicillins and cephalosporins are the most important class of beta (β) lactam antibiotics, accounting for 65% total antibiotic market. Penicillins are produced by Penicillium rubens (popularly known as P. chrysogenum) were used to synthesize the active pharmaceutical intermediate (API), 6-aminopenicillinic acid (6-APA) employed in semisynthetic antibiotic production. The wild strains produce a negligible amount of penicillin (Pen). High antibiotic titre-producing P. chrysogenum strains are necessitating for industrial Pen production to meet global demand at lower prices. Classical strain improvement (CSI) approaches such as random mutagenesis, medium engineering, and fermentation are the cornerstones for high-titer Pen production. Since, Sir Alexander Fleming Discovery of Pen, great efforts are expanded to develop at a commercial scale antibiotics producing strains. Breakthroughs in genetic engineering, heterologous expression and CRISPR/Cas9 genome editing tools opened a new window for Pen production at a commercial scale to assure health crisis. The current state of knowledge, limitations of CSI and genetic engineering approaches to Pen production are discussed in this review.

Developing fungal heterologous expression platforms to explore and improve the production of natural products from fungal biodiversity

Natural products from fungi represent an important source of biologically active metabolites notably for therapeutic agent development. Genome sequencing revealed that the number of biosynthetic gene clusters (BGCs) in fungi is much larger than expected. Unfortunately, most of them are silent or barely expressed under laboratory culture conditions. Moreover, many fungi in nature are uncultivable or cannot be genetically manipulated, restricting the extraction and identification of bioactive metabolites from these species. Rapid exploration of the tremendous number of cryptic fungal BGCs necessitates the development of heterologous expression platforms, which will facilitate the efficient production of natural products in fungal cell factories. Host selection, BGC assembly methods, promoters used for heterologous gene expression, metabolic engineering strategies and compartmentalization of biosynthetic pathways are key aspects for consideration to develop such a microbial platform. In the present review, we summarize current progress on the above challenges to promote research effort in the relevant fields.

Microbial production of small peptide: pathway engineering and synthetic biology

Small peptides are a group of natural products with low molecular weights and complex structures. The diverse structures of small peptides endow them with broad bioactivities and suggest their potential therapeutic use in the medical field. The remaining challenge is methods to address the main limitations, namely (i) the low amount of available small peptides from natural sources, and (ii) complex processes required for traditional chemical synthesis. Therefore, harnessing microbial cells as workhorse appears to be a promising approach to synthesize these bioactive peptides. As an emerging engineering technology, synthetic biology aims to create standard, well-characterized and controllable synthetic systems for the biosynthesis of natural products. In this review, we describe the recent developments in the microbial production of small peptides. More importantly, synthetic biology approaches are considered for the production of small peptides, with an emphasis on chassis cells, the evolution of biosynthetic pathways, strain improvements and fermentation.

Membrane traffic related to endosome dynamics and protein secretion in filamentous fungi

In eukaryotic cells, membrane-surrounded organelles are orchestrally organized spatiotemporally under environmental situations. Among such organelles, vesicular transports and membrane contacts occur to communicate each other, so-called membrane traffic. Filamentous fungal cells are highly polarized and thus membrane traffic is developed to have versatile functions. Early endosome (EE) is an endocytic organelle that dynamically exhibits constant long-range motility through the hyphal cell, which is proven to have physiological roles, such as other organelle distribution and signal transduction. Since filamentous fungal cells are also considered as cell factories, to produce valuable proteins extracellularly, molecular mechanisms of secretory pathway including protein glycosylation have been well investigated. In this review, molecular and physiological aspects of membrane traffic especially related to EE dynamics and protein secretion in filamentous fungi are summarized, and perspectives for application are also described.

Something old, something new: challenges and developments in Aspergillus niger biotechnology

The filamentous ascomycete fungus Aspergillus niger is a prolific secretor of organic acids, proteins, enzymes and secondary metabolites. Throughout the last century, biotechnologists have developed A. niger into a multipurpose cell factory with a product portfolio worth billions of dollars each year. Recent technological advances, from genome editing to other molecular and omics tools, promise to revolutionize our understanding of A. niger biology, ultimately to increase efficiency of existing industrial applications or even to make entirely new products. However, various challenges to this biotechnological vision, many several decades old, still limit applications of this fungus. These include an inability to tightly control A. niger growth for optimal productivity, and a lack of high-throughput cultivation conditions for mutant screening. In this mini-review, we summarize the current state-of-the-art for A. niger biotechnology with special focus on organic acids (citric acid, malic acid, gluconic acid and itaconic acid), secreted proteins and secondary metabolites, and discuss how new technological developments can be applied to comprehensively address a variety of old and persistent challenges.

Fusarium verticillioides FvPex8 Is a Key Component of the Peroxisomal Docking/Translocation Module That Serves Important Roles in Fumonisin Biosynthesis but Not in Virulence

Peroxisomes are ubiquitous organelles in eukaryotes that fulfill various important metabolic functions. In this study, we investigated the role of docking/translocation module (DTM) peroxins, mainly FvPex8, FvPex13, FvPex14, and FvPex33, in Fusarium verticillioides development, virulence, and fumonisin B₁ (FB₁) biosynthesis. Protein interaction experiments suggested that FvPex13 serves as the central DTM subunit in F. verticillioides. Notably, FvPex8 and FvPex14 did not show direct interaction in our experiments. We generated gene-deletion mutants (ΔFvpex8, ΔFvpex13, ΔFvpex14, ΔFvpex33, ΔFvpex33/14) and further examined the functional role of these peroxins. Deletion mutants exhibited disparity in carbon nutrient utilization and defect in cell-wall integrity when stress agents were applied. Under nutrient starvation, mutants also showed higher levels of lipid droplet accumulation. Particularly, ΔFvpex8 mutant showed significant FB₁ reduction and altered expression of key FB₁ biosynthesis genes. However, FvPex13 was primarily responsible for asexual conidia reproduction and virulence, while the ΔFvpex33/14 double mutant also showed a virulence defect. In summary, our study suggests that FvPex13 is the central component of DTM, with direct physical interaction with other DTM peroxins, and regulates peroxisome membrane biogenesis as well as PTS1- and PTS2-mediated transmembrane cargo transportation. Importantly, we also characterized FvPex8 as a key component in F. verticillioides DTM that affects peroxisome function and FB₁ biosynthesis.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Membrane Traffic in Aspergillus oryzae and Related Filamentous Fungi

The industrially important filamentous fungus Aspergillus oryzae, known as the yellow Koji mold and also designated the Japanese National fungus, has been investigated for understanding the intracellular membrane trafficking machinery due to the great ability of valuable enzyme production. The underlying molecular mechanisms of the secretory pathway delineate the main secretion route from the hyphal tip via the vesicle cluster Spitzenkörper, but also there is a growing body of evidence that septum-directed and unconventional secretion occurs in A. oryzae hyphal cells. Moreover, not only the secretory pathway but also the endocytic pathway is crucial for protein secretion, especially having a role in apical endocytic recycling. As a hallmark of multicellular filamentous fungal cells, endocytic organelles early endosome and vacuole are quite dynamic: the former exhibits constant long-range motility through the hyphal cells and the latter displays pleiomorphic structures in each hyphal region. These characteristics are thought to have physiological roles, such as supporting protein secretion and transporting nutrients. This review summarizes molecular and physiological mechanisms of membrane traffic, i.e., secretory and endocytic pathways, in A. oryzae and related filamentous fungi and describes the further potential for industrial applications.

The sulfur metabolism regulator MetR is a global regulator controlling phytochrome-dependent light responses in Aspergillus nidulans

Phytochrome-dependent light signaling has been studied in several fungi. In Aspergillus nidulans light-stimulated phytochrome activates the high-osmolarity glycerol (HOG) signaling pathway and thereby controls the expression of a large number of genes, many of which are related to stress responses. In a genome-wide expression analysis in A. nidulans we found that phytochrome, fphA, is under strict expression control of the central regulator of the sulfur-starvation response, MetR. This transcriptional regulator is required for the expression of genes involved in inorganic sulfur assimilation. In the presence of organic sulfur, MetR is probably ubiquitinated and possibly degraded and the transcription of sulfur-assimilation genes, e.g., sulfate permease, is turned off. The expression analysis described here revealed, however, that MetR additionally controls the expression of hundreds of genes, many of which are required for secondary metabolite production. We also show that metR mutation phenocopies fphA deletion, and five other histidine-hybrid kinases are down-regulated in the metR1 mutant. Furthermore, we found that light and phytochrome regulate the expression of at least three carbon-sulfur hydrolases. This work is a further step towards understanding the interplay between light sensing and metabolic pathways.

Fungal natural products galaxy: Biochemistry and molecular genetics toward blockbuster drugs discovery

Secondary metabolites synthesized by fungi have become a precious source of inspiration for the design of novel drugs. Indeed, fungi are prolific producers of fascinating, diverse, structurally complex, and low-molecular-mass natural products with high therapeutic leads, such as novel antimicrobial compounds, anticancer compounds, immunosuppressive agents, among others. Given that these microorganisms possess the extraordinary capacity to secrete diverse chemical scaffolds, they have been highly exploited by the giant pharma companies to generate small molecules. This has been made possible because the isolation of metabolites from fungal natural sources is feasible and surpasses the organic synthesis of compounds, which otherwise remains a significant bottleneck in the drug discovery process. Here in this comprehensive review, we have discussed recent studies on different fungi (pathogenic, non-pathogenic, commensal, and endophytic/symbiotic) from different habitats (terrestrial and marines), the specialized metabolites they biosynthesize, and the drugs derived from these specialized metabolites. Moreover, we have unveiled the logic behind the biosynthesis of vital chemical scaffolds, such as NRPS, PKS, PKS-NRPS hybrid, RiPPS, terpenoids, indole alkaloids, and their genetic mechanisms. Besides, we have provided a glimpse of the concept behind mycotoxins, virulence factor, and host immune response based on fungal infections.

Compartmentalized biosynthesis of fungal natural products

Fungal natural products (NPs) with diverse chemical structures and biological activities are rich resources of both drugs and toxins, thus causing Janus-like effects on human beings. Significant progress has been made in discovery and mining of novel fungal NPs in the past decades. Unlike prokaryotic organisms, eukaryotic cells of fungi have discrete organelles to form compartmentalized assembly lines for the highly ordered and hence efficient biosynthesis of fungal NPs. In this review, we summarize a limited but growing number of studies on compartmentalized biosynthesis of fungal NPs. The emerging strategies and efforts for engineering of subcellular localization of relevant biosynthetic enzymes are also discussed. We expect to provide some new insights and perspectives on the more complex NP biogenesis in higher microorganisms.

Production of the Fragrance Geraniol in Peroxisomes of a Product-Tolerant Baker's Yeast

Monoterpenoids, such as the plant metabolite geraniol, are of high industrial relevance since they are important fragrance materials for perfumes, cosmetics, and household products. Chemical synthesis or extraction from plant material for industry purposes are complex, environmentally harmful or expensive and depend on seasonal variations. Heterologous microbial production offers a cost-efficient and sustainable alternative but suffers from low metabolic flux of the precursors and toxicity of the monoterpenoid to the cells. In this study, we evaluated two approaches to counteract both issues by compartmentalizing the biosynthetic enzymes for geraniol to the peroxisomes of Saccharomyces cerevisiae as production sites and by improving the geraniol tolerance of the yeast cells. The combination of both approaches led to an 80% increase in the geraniol titers. In the future, the inclusion of product tolerance and peroxisomal compartmentalization into the general chassis engineering toolbox for monoterpenoids or other host-damaging, industrially relevant metabolites may lead to an efficient, low-cost, and eco-friendly microbial production for industrial purposes.

Transport systems, intracellular traffic of intermediates and secretion of β-lactam antibiotics in fungi

Fungal secondary metabolites are synthesized by complex biosynthetic pathways catalized by enzymes located in different subcellular compartments, thus requiring traffic of precursors and intermediates between them. The β-lactam antibiotics penicillin and cephalosporin C serve as an excellent model to understand the molecular mechanisms that control the subcellular localization of secondary metabolites biosynthetic enzymes. Optimal functioning of the β-lactam biosynthetic enzymes relies on a sophisticated temporal and spatial organization of the enzymes, the intermediates and the final products. The first and second enzymes of the penicillin pathway, ACV synthetase and IPN synthase, in Penicillium chrysogenum and Aspergillus nidulans are cytosolic. In contrast, the last two enzymes of the penicillin pathway, phenylacetyl-CoA ligase and isopenicillin N acyltransferase, are located in peroxisomes working as a tandem at their optimal pH that coincides with the peroxisomes pH. Two MFS transporters, PenM and PaaT have been found to be involved in the import of the intermediates isopenicillin N and phenylacetic acid, respectively, into peroxisomes. Similar compartmentalization of intermediates occurs in Acremonium chrysogenum; two enzymes isopenicillin N-CoA ligase and isopenicillin N-CoA epimerase, that catalyse the conversion of isopenicillin N in penicillin N, are located in peroxisomes. Two genes encoding MFS transporters, cefP and cefM, are located in the early cephalosporin gene cluster. These transporters have been localized in peroxisomes by confocal fluorescence microscopy. A third gene of A. chrysogenum, cefT, encodes an MFS protein, located in the cell membrane involved in the secretion of cephalosporin C, although cefT-disrupted mutants are still able to export cephalosporin by redundant transporters. The secretion of penicillin from peroxisomes to the extracellular medium is still unclear. Attempts have been made to identify a gene encoding the penicillin secretion protein among the 48 ABC-transporters of P. chrysogenum. The highly efficient secretion system that exports penicillin against a concentration gradient may involve active penicillin extrusion systems mediated by vesicles that fuse to the cell membrane. However, there is no correlation of pexophagy with penicillin or cephalosporin formation since inactivation of pexophagy leads to increased penicillin or cephalosporin biosynthesis due to preservation of peroxisomes. The penicillin biosynthesis finding shows that in order to increase biosynthesis of novel secondary metabolites it is essential to adequately target enzymes to organelles.

On the role of the global regulator RlcA in red-light sensing in Aspergillus nidulans

A large proportion of fungal genomes are under the control of light. Most fungi employ complex light sensing systems, consisting of red-, blue-, and in some cases green-light photoreceptors. Here we studied the light response in Aspergillus nidulans. In a genetic screen, followed by whole-genome sequencing we identified a global regulator, which appears to be involved in chromatin structure modification. We therefore named the protein RlcA (regulator of light sensing and chromatin remodeling). The protein comprises a nuclear localization signal, a PHD (plant homeodomain) finger, a TFSII (found in the central region of the transcription elongation factor S-II), and a SPOC domain (Spen paralog and ortholog C-terminal domain). In the mutant, where light-controlled genes were constitutively active, the SPOC domain is missing. RlcA localized to the nucleus and interacted with the phytochrome FphA. The PHD-finger domain probably binds to trimethylated lysine 4 of histone H3, whereas the TFSII domain binds RNA polymerase II. The SPOC domain could mediate interaction with a global repressor protein. In the mutant, repressor recruitment would be hindered, whereas in the wild type repressor release would be induced after light stimulation. Our results add another layer of complexity to light sensing in filamentous fungi.

Advanced strategy for metabolite exploration in filamentous fungi

Filamentous fungi comprise an abundance of gene clusters that encode high-value metabolites, whereas affluent gene clusters remain silent during laboratory conditions. Complex cellular metabolism further limits these metabolite yields. Therefore, diverse strategies such as genetic engineering and chemical mutagenesis have been developed to activate these cryptic pathways and improve metabolite productivity. However, lower efficiencies of gene modifications and screen tools delayed the above processes. To address the above issues, this review describes an alternative design-construction evaluation optimization (DCEO) approach. The DCEO tool provides theoretical and practical principles to identify potential pathways, modify endogenous pathways, integrate exogenous pathways, and exploit novel pathways for their diverse metabolites and desirable productivities. This DCEO method also offers different tactics to balance the cellular metabolisms, facilitate the genetic engineering, and exploit the scalable metabolites in filamentous fungi.

Dissection of patulin biosynthesis, spatial control and regulation mechanism in Penicillium expansum

The patulin biosynthesis is one of model pathways in an understanding of secondary metabolite biology and network novelties in fungi. However, molecular regulation mechanism of patulin biosynthesis and contribution of each gene related to the different catalytic enzymes in the biochemical steps of the pathway remain largely unknown in fungi. In this study, the genetic components of patulin biosynthetic pathway were systematically dissected in Penicillium expansum, which is an important fungal pathogen and patulin producer in harvested fruits and vegetables. Our results revealed that all the 15 genes in the cluster are involved in patulin biosynthesis. Proteins encoded by those genes are compartmentalized in various subcellular locations, including cytosol, nucleus, vacuole, endoplasmic reticulum, plasma membrane and cell wall. The subcellular localizations of some proteins, such as PatE and PatH, are required for the patulin production. Further, the functions of eight enzymes in the 10-step patulin biosynthetic pathway were verified in P. expansum. Moreover, velvet family proteins, VeA, VelB and VelC, were proved to be involved in the regulation of patulin biosynthesis, but not VosA. These findings provide a thorough understanding of the biosynthesis pathway, spatial control and regulation mechanism of patulin in fungi.

Repurposing peroxisomes for microbial synthesis for biomolecules

Microbial synthesis represents an alternative approach for the sustainable production of chemicals, fuels, and medicines. However, construction of biosynthetic pathways always suffers from side reactions, toxicity of intermediates, or low efficiency of substrate channeling. Subcellular compartmentalization may contribute to a more efficient production of target products by reducing side reactions and toxic effects within a compact insular space. The peroxisome, a type of organelle that is involved in catabolism of fatty acids and reactive oxygen species, has attracted a great deal of attention in the construction of eukaryotic cell factories with little impact on essential cellular function. In this chapter, we will systematically review recent advances in peroxisomal compartmentalization for microbial production of valuable biomolecules. Additionally, detailed experimental designs and protocols are also described. We hope a comprehensive understanding of peroxisomes will promote their application in metabolic engineering and synthetic biology.

Strategies for Engineering Natural Product Biosynthesis in Fungi

Fungi are a prolific source of bioactive compounds, some of which have been developed as essential medicines and life-enhancing drugs. Genome sequencing has revealed that fungi have the potential to produce considerably more natural products (NPs) than are typically observed in the laboratory. Recently, there have been significant advances in the identification, understanding, and engineering of fungal biosynthetic gene clusters (BGCs). This review briefly describes examples of the engineering of fungal NP biosynthesis at the global, pathway, and enzyme level using in vivo and in vitro approaches and refers to the range and scale of heterologous expression systems available, developments in combinatorial biosynthesis, progress in understanding how fungal BGCs are regulated, and the applications of these novel biosynthetic enzymes as biocatalysts.

Pathway Design, Engineering, and Optimization

The microbial metabolic versatility found in nature has inspired scientists to create microorganisms capable of producing value-added compounds. Many endeavors have been made to transfer and/or combine pathways, existing or even engineered enzymes with new function to tractable microorganisms to generate new metabolic routes for drug, biofuel, and specialty chemical production. However, the success of these pathways can be impeded by different complications from an inherent failure of the pathway to cell perturbations. Pursuing ways to overcome these shortcomings, a wide variety of strategies have been developed. This chapter will review the computational algorithms and experimental tools used to design efficient metabolic routes, and construct and optimize biochemical pathways to produce chemicals of high interest.

Quantifying the efficiency of Saccharomyces cerevisiae translocation tags

Compartmentalization of metabolic pathways into organelles of the yeast Saccharomyces cerevisiae has been used to improve chemical production. Pathway compartmentalization aids chemical production by bringing enzymes into close proximity to one another, placing enzymes near key starting metabolites or essential co-factors, increasing the effective concentration of metabolic intermediates, and providing a more suitable chemical environment for enzymatic activity. Although several translocation tags have been used to localize enzymes to different yeast organelles, their translocation efficiencies have not been quantified. Here, we systematically quantify the translocation efficiencies of 10 commonly used S. cerevisiae tags by localizing green fluorescent protein (GFP) into three yeast organelles: the mitochondrion (4 tags), the vacuole (3 tags), and the peroxisome (3 tags). Further, we investigate whether plasmid copy number or mRNA levels vary with tag translocation efficiency. Quantification of the efficiencies of S. cerevisiae translocation tags provides an important resource for bioengineering practitioners when choosing a tag to compartmentalize their desired protein. Finally, these efficiencies can be used to determine the percentage of enzyme compartmentalization and, thus, help better quantify effects of compartmentalization on metabolic pathway efficiency.

Genetic engineering of Ganoderma lucidum for the efficient production of ganoderic acids

Ganoderma lucidum is a well-known traditional medicinal mushroom that produces ganoderic acids with numerous interesting bioactivities. Genetic engineering is an efficient approach to improve ganoderic acid biosynthesis. However, reliable genetic transformation methods and appropriate genetic manipulation strategies remain underdeveloped and thus should be enhanced. We previously established a homologous genetic transformation method for G. lucidum; we also applied the established method to perform the deregulated overexpression of a homologous 3-hydroxy-3-methyl-glutaryl coenzyme A reductase gene in G. lucidum. Engineered strains accumulated more ganoderic acids than wild-type strains. In this report, the genetic transformation systems of G. lucidum are described; current trends are also presented to improve ganoderic acid production through the genetic manipulation of G. lucidum.

Fungi use the SakA (HogA) pathway for phytochrome-dependent light signalling

Stress-sensing in fungi depends on a signalling cascade comprised of a two-component phosphorylation relay plus a subsequent MAP kinase cascade to trigger gene expression. Besides osmotic or oxidative stress, fungi sense many other environmental factors, one of which is light(1,2). Light controls morphogenetic pathways but also the production of secondary metabolites such as penicillin. Here we show that phytochrome-dependent light signalling in Aspergillus nidulans involves the stress-sensing and osmosensing signalling pathway. In a screening for 'blind' mutants, the MAP kinase SakA (also known as HogA) was identified by whole-genome sequencing. The phytochrome FphA physically interacted with the histidine-containing phosphotransfer protein YpdA and caused light-dependent phosphorylation of the MAP kinase SakA and its shuttling into nuclei. In the absence of phytochrome, SakA still responded to osmotic stress but not to light. The SakA pathway thus integrates several stress factors and can be considered to be a hub for environmental signals.

Translating biosynthetic gene clusters into fungal armor and weaponry

Filamentous fungi are renowned for the production of a diverse array of secondary metabolites (SMs) where the genetic material required for synthesis of a SM is typically arrayed in a biosynthetic gene cluster (BGC). These natural products are valued for their bioactive properties stemming from their functions in fungal biology, key among those protection from abiotic and biotic stress and establishment of a secure niche. The producing fungus must not only avoid self-harm from endogenous SMs but also deliver specific SMs at the right time to the right tissue requiring biochemical aid. This review highlights functions of BGCs beyond the enzymatic assembly of SMs, considering the timing and location of SM production and other proteins in the clusters that control SM activity. Specifically, self-protection is provided by both BGC-encoded mechanisms and non-BGC subcellular containment of toxic SM precursors; delivery and timing is orchestrated through cellular trafficking patterns and stress- and developmental-responsive transcriptional programs.

A 3-Vinyl Cephem Derivative, a Useful Intermediate in the Synthesis of Cepham Antibiotics, from Aspergillus awamori Associated with Banana Fruit

Aspergillus awamori was isolated from a diseased banana fruit, Musa acuminata cv. Ambul. The fungus was fermented in potato dextrose broth and on potato dextrose agar media and the fungal media were extracted with EtOAc. Chromatographic separation of the EtOAc extracts furnished 4-methoxybenzyl 7-phenylacetamido-3-vinyl-3-cephem-4-carboxylate (1), along with three naphtho-γ-pyrones, flavasperone (2), foncesinone A (3) and aurasperone A (4), and three alkaloids, aspernigrin A (5), pestalamide C (6) and nigragillin (7). Compound 1, a known key intermediate in the chemical synthesis of cepham antibiotics, was isolated from a natural source for the first time. Compound 1 is the first 3-vinyl cephem derivative of microbial origin.

Synthetic biology of fungal natural products

Synthetic biology is an ever-expanding field in science, also encompassing the research area of fungal natural product (NP) discovery and production. Until now, different aspects of synthetic biology have been covered in fungal NP studies from the manipulation of different regulatory elements and heterologous expression of biosynthetic pathways to the engineering of different multidomain biosynthetic enzymes such as polyketide synthases or non-ribosomal peptide synthetases. The following review will cover some of the exemplary studies of synthetic biology in filamentous fungi showing the capacity of these eukaryotes to be used as model organisms in the field. From the vast array of different NPs produced to the ease for genetic manipulation, filamentous fungi have proven to be an invaluable source for the further development of synthetic biology tools.

Cellular compartmentalization of secondary metabolism

Fungal secondary metabolism is often considered apart from the essential housekeeping functions of the cell. However, there are clear links between fundamental cellular metabolism and the biochemical pathways leading to secondary metabolite synthesis. Besides utilizing key biochemical precursors shared with the most essential processes of the cell (e.g., amino acids, acetyl CoA, NADPH), enzymes for secondary metabolite synthesis are compartmentalized at conserved subcellular sites that position pathway enzymes to use these common biochemical precursors. Co-compartmentalization of secondary metabolism pathway enzymes also may function to channel precursors, promote pathway efficiency and sequester pathway intermediates and products from the rest of the cell. In this review we discuss the compartmentalization of three well-studied fungal secondary metabolite biosynthetic pathways for penicillin G, aflatoxin and deoxynivalenol, and summarize evidence used to infer subcellular localization. We also discuss how these metabolites potentially are trafficked within the cell and may be exported.