Increasing Lovastatin Production by Re-routing the Precursors Flow of Aspergillus terreus via Metabolic Engineering

Efficient metabolic pathway modification in various strains of lactic acid bacteria using CRISPR/Cas9 system for elevated synthesis of antimicrobial compounds

Lactic acid bacteria (LAB) are known to exhibit various beneficial roles in fermentation, serving as probiotics, and producing a plethora of valuable compounds including antimicrobial activity such as bacteriocin-like inhibitory substance (BLIS) that can be used as biopreservative to improve food safety and quality. However, the yield of BLIS is often limited, which poses a challenge to be commercially competitive with the current preservation practice. Therefore, the present work aimed to establish an optimised two-plasmid CRISPR/Cas9 system to redirect the carbon flux away from lactate towards compounds with antimicrobial activity by disrupting lactate dehydrogenase gene (ldh) on various strains of LAB. The lactic acid-deficient (ldhΔ) strains caused a metabolic shift resulting in increased inhibitory activity against selected foodborne pathogens up to 78 % than the wild-type (WT) strain. The most significant effect was depicted by Enterococcus faecalis-ldh∆ which displayed prominent bactericidal effects against all foodborne pathogens as compared to the WT that showed no antimicrobial activity. The present work provided a framework model for economically important LAB and other beneficial bacteria to synthesise and increase the yield of valuable food and industrial compounds. The present work reported for the first time that the metabolism of selected LAB can be manipulated by modifying ldh to attain metabolites with higher antimicrobial activity.

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.

Genetic regulation of L-tryptophan metabolism in Psilocybe mexicana supports psilocybin biosynthesis

BACKGROUND

Although Basidiomycota produce pharmaceutically and ecologically relevant natural products, knowledge of how they coordinate their primary and secondary metabolism is virtually non-existent. Upon transition from vegetative mycelium to carpophore formation, mushrooms of the genus Psilocybe use L-tryptophan to supply the biosynthesis of the psychedelic tryptamine alkaloid psilocybin with the scaffold, leading to a strongly increased demand for this particular amino acid as this alkaloid may account for up to 2% of the dry mass. Using Psilocybe mexicana as our model and relying on genetic, transcriptomic, and biochemical methods, this study investigated if L-tryptophan biosynthesis and degradation in P. mexicana correlate with natural product formation.

RESULTS

A comparative transcriptomic approach of gene expression in P. mexicana psilocybin non-producing vegetative mycelium versus producing carpophores identified the upregulation of L-tryptophan biosynthesis genes. The shikimate pathway genes trpE1, trpD, and trpB (encoding anthranilate synthase, anthranilate phosphoribosyltransferase, and L-tryptophan synthase, respectively) were upregulated in carpophores. In contrast, genes idoA and iasA, encoding indole-2,3-dioxygenase and indole-3-acetaldehyde synthase, i.e., gateway enzymes for L-tryptophan-consuming pathways, were massively downregulated. Subsequently, IasA was heterologously produced in Escherichia coli and biochemically characterized in vitro. This enzyme represents the first characterized microbial L-tryptophan-preferring acetaldehyde synthase. A comparison of transcriptomic data collected in this study with prior data of Psilocybe cubensis showed species-specific differences in how L-tryptophan metabolism genes are regulated, despite the close taxonomic relationship.

CONCLUSIONS

The upregulated L-tryptophan biosynthesis genes and, oppositely, the concomitant downregulated genes encoding L-tryptophan-consuming enzymes reflect a well-adjusted cellular system to route this amino acid toward psilocybin production. Our study has pilot character beyond the genus Psilocybe and provides, for the first time, insight in the coordination of mushroom primary and secondary metabolism.

Whole genome sequence characterization of Aspergillus terreus ATCC 20541 and genome comparison of the fungi A. terreus

Aspergillus terreus is well-known for lovastatin and itaconic acid production with biomedical and commercial importance. The mechanisms of metabolite formation have been extensively studied to improve their yield through genetic engineering. However, the combined repertoire of carbohydrate-active enzymes (CAZymes), cytochrome P450s (CYP) enzymes, and secondary metabolites (SMs) in the different A. terreus strains has not been well studied yet, especially with respect to the presence of biosynthetic gene clusters (BGCs). Here we present a 30 Mb whole genome sequence of A. terreus ATCC 20541 in which we predicted 10,410 protein-coding genes. We compared the CAZymes, CYPs enzyme, and SMs across eleven A. terreus strains, and the results indicate that all strains have rich pectin degradation enzyme and CYP52 families. The lovastatin BGC of lovI was linked with lovF in A. terreus ATCC 20541, and the phenomenon was not found in the other strains. A. terreus ATCC 20541 lacked a non-ribosomal peptide synthetase (AnaPS) participating in acetylaszonalenin production, which was a conserved protein in the ten other strains. Our results present a comprehensive analysis of CAZymes, CYPs enzyme, and SM diversities in A. terreus strains and will facilitate further research in the function of BGCs associated with valuable SMs.

Co-cultivation of filamentous microorganisms in the presence of aluminum oxide microparticles

In the present work, the approaches of submerged co-cultivation and microparticle-enhanced cultivation (MPEC) were combined and evaluated over the course of three case studies. The filamentous fungus Aspergillus terreus was co-cultivated with Penicillium rubens, Streptomyces rimosus, or Cerrena unicolor in shake flasks with or without the addition of aluminum oxide microparticles. The influence of microparticles on the production of lovastatin, penicillin G, oxytetracycline, and laccase in co-cultures was compared with the effects recorded for the corresponding monocultures. In addition, the quantitative analyses of morphological parameters, sugars consumption, and by-products formation were performed. The study demonstrated that the influence of microparticles on the production of a given molecule in mono- and co-culture may differ considerably, e.g., the biosynthesis of oxytetracycline was shown to be inhibited due to the presence of aluminum oxide in "A. terreus vs. S. rimosus" co-cultivation variants but not in S. rimosus monocultures. The differences were also observed regarding the morphological characteristics, e.g., the microparticles-induced changes of projected area in the co-cultures and the corresponding monocultures were not always comparable. In addition, the study showed the importance of medium composition on the outcomes of MPEC, as exemplified by lovastatin production in A. terreus monocultures. Finally, the co-cultures of A. terreus with a white-rot fungus C. unicolor were described here for the first time. KEY POINTS: • Aluminum oxide affects secondary metabolites production in submerged co-cultures. • Mono- and co-cultures are differently impacted by the addition of aluminum oxide. • Effect of aluminum oxide on metabolites production depends on medium composition.

Heterologous Synthesis of Monacolin J by Reconstructing Its Biosynthetic Gene Cluster in Aspergillus niger

Monacolin J (MJ), a key precursor of Lovastatin, could synthesize important statin drug simvastatin by hydrolyzing lovastatin and adding different side chains. In this study, to reduce the cumbersome hydrolysis of lovastatin to produce MJ in the native strain Aspergillus terreus, the MJ biosynthetic pathway genes (lovB, lovC, lovG, and lovA) were heterologously integrated into the genome of Aspergillus. niger CBS513.88 with strong promoters and suitable integration sites, via yeast 2μ homologous recombination to construct expression cassettes of long-length genes and CRISPR/Cas9 homology-directed recombination (CRISPR-HDR) to integrate MJ genes in the genome of A. niger. RT-PCR results proved that pathway synthesis-related genes could be heterologously expressed in A. niger. Finally, we constructed an engineered strain that could produce monacolin J, detected by LC-HR-ESIMS (MJ, 339.22 [M-H]⁺). The yield of MJ reached 92.90 mg/L after 7-day cultivation. By optimizing the cultivation conditions and adding precursor, the final titer of MJ was 142.61 mg/L on the fourth day of fed-batch cultivation, which was increased by 53.5% compared to the original growth conditions. Due to the wide application of A. niger in industrial fermentation for food and medicine, the following work will be dedicated to optimizing the metabolic network to improve the MJ production in the engineered strain.