Transcriptome analysis of malate-induced Schizochytrium sp. FJU-512 reveals a novel pathway for biosynthesis of docosahexaenoic acid with enhanced expression of genes responsible for acetyl-CoA and NADPH accumulation.

Schizochytrium is one of the few oleaginous microalgae that produce docosahexaenoic acid (DHA)-rich lipids. In this study, global changes in gene expression levels of Schizochytrium sp. FJU-512 cultured with malate in a 15 l-bioreactor was analyzed using comparative transcriptomics. The changes were found mainly in the genes involved in oxidative phosphorylation, ß-oxidation, and pentose phosphate pathways. Consequently, the global changes in genes associated with the pathways could lead to an increase in the influx throughputs of pyruvate, branched-chain amino acids, fatty acids, and vitamin B6. Our transcriptome analysis indicated pyruvate dehydrogenase E2 component and acetolactate synthase I/II/III large subunit as major contributors to acetyl-CoA biosynthesis, whereas glucose-6-phosphate dehydrogenase was indicated as the major contributor to the biosynthesis of NADPH. An increase in DHA titer of up to 22% was achieved with the addition of malate to the fed-batch culture of Schizochytrium sp. FJU-512. This study provides an alternate method to enhance DHA production in Schizochytrium sp. FJU-512 through malate induced upregulation of genes responsible for acetyl-CoA and NADPH biosynthesis.

Engineering artificial photosynthetic life-forms through endosymbiosis.

The evolutionary origin of the photosynthetic eukaryotes drastically altered the evolution of complex lifeforms and impacted global ecology. The endosymbiotic theory suggests that photosynthetic eukaryotes evolved due to endosymbiosis between non-photosynthetic eukaryotic host cells and photosynthetic cyanobacterial or algal endosymbionts. The photosynthetic endosymbionts, propagating within the cytoplasm of the host cells, evolved, and eventually transformed into chloroplasts. Despite the fundamental importance of this evolutionary event, we have minimal understanding of this remarkable evolutionary transformation. Here, we design and engineer artificial, genetically tractable, photosynthetic endosymbiosis between photosynthetic cyanobacteria and budding yeasts. We engineer various mutants of model photosynthetic cyanobacteria as endosymbionts within yeast cells where, the engineered cyanobacteria perform bioenergetic functions to support the growth of yeast cells under defined photosynthetic conditions. We anticipate that these genetically tractable endosymbiotic platforms can be used for evolutionary studies, particularly related to organelle evolution, and also for synthetic biology applications.

Heterologous expression of a natural product biosynthetic gene cluster from Cordyceps militaris.

Cordyceps is a genus of ascomycete fungi widely used in old Chinese medicine, and many investigations have focus on uncovering their biological activities. Until now, only a few compounds have been identified from Cordyceps, mainly due to their poor yield. So as to make full use of Cordyceps, we used the strategy of genome mining and heterologous expression to discover natural products (NPs) from Cordyceps militaris. Analysis of the genome sequence of Cordyceps militaris CM01 showed the presence of a cryptic gene cluster encoding a highly-reducing polyketide synthetase (HR-PKS), enoyl-reductase (ER) and cytochrome P450. Heterologous expression in Aspergillus nidulans enabled the identification of two new polyketides, cordypyrone A and B. Their structures were determined by 1D and 2D NMR techniques. They showed only modest activities against pathogenic bacteria including methicillin-resistant Staphylococcus aureus (MRSA), Mycobacteria tuberculosis and Bacillus cereus.

Heterologous Expression of Macrollins from Phytopathogenic Macrophomina phaseolina Revealed a Cytochrome P450 Mono-oxygenase in the Biosynthesis of ß-Hydroxyl Tetramic Acid.

Macrophomina phaseolina (M. phaseolina) is a crucial pathogenic fungus that can cause severe charcoal rot in economic crops and other plants. In this study, four new natural products, macrollins A-D, were discovered from M. phaseolina by the strategy of heterologous expression. To our knowledge, macrollins are the first reported polyketide-amino acid hybrids from the plant pathogen. Heterologous expression and in vitro reactions revealed a cytochrome P450 mono-oxygenase (MacC) catalyzing the hydroxylation at the ß-carbon of tetramic acid molecules, which is different from P450s leading to the ring expansion in the biosynthesis of fungal 2-pyridones. Phylogenetic analysis of P450s involved in the fungal polyketide-amino acid hybrids showed that MacC was not classified in any known clades. The putative oxidative mechanisms of the P450s and the biosynthetic pathway of macrollins were also proposed.

Structural Insights into the Trans-Acting Enoyl Reductase in the Biosynthesis of Long-Chain Polyunsaturated Fatty Acids in Shewanella piezotolerans.

Two long-chain polyunsaturated fatty acids (LC-PUFAs), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), play vital roles in human health. Similarly, two biosynthetic pathways, based on desaturase/elongase and polyketide synthase, have been implicated in the synthesis of microbial LC-PUFA. Up to now, only several microalgae, no bacteria, have been used in the commercial production of oils rich in DHA and/or EPA. Fully understanding the enzymatic mechanism in the biosynthesis of LC-PUFA would contribute significantly to produce EPA and/or DHA by the bacteria. In this study, we report a 1.998 Å-resolution crystal structure of trans-acting enoyl reductase (ER), SpPfaD, from Shewanella piezotolerans. The SpPfaD model consists of one homodimer in the asymmetric unit, and each subunit contains three domains. These include an N-terminal, a central domain forming a classic TIM barrel with a single FMN cofactor molecule bound atop the barrel, and a C-terminal domain with a lid above the TIM barrel. Furthermore, we docked oxidized nicotinamide adenine dinucleotide phosphate (NADP) and an inhibitor 2-(4-(2-((3-(5-(pyridin-2-ylthio)thiazol-2-yl)ureido)methyl)-1H-imidazole-4-yl)phenoxy)acetic acid (TUI) molecule into the active site and analyzed the inhibition and catalytic mechanisms of the enoyl reductase SpPfaD. To the best of our knowledge, this is the first crystal structure of trans-ER in the biosynthesis of bacterial polyketides.

Isolation and characterization of a new cytotoxic polyketide-amino acid hybrid from Thermothelomyces thermophilus ATCC 42464.

Fungi are a rich source of novel anticancer compounds. Bioassay-guided isolation has led to the isolation of four polyketide-amino acid hybrid compounds with trans-fused decalin system from the fungus Thermothelomyces thermophilus ATCC 42464 (=Myceliophthora thermophila ATCC 42464): myceliothermophins A, B, E and F (1-4). The structure of the new compound (myceliothermophin F, compound 4) was clearly determined by a combination of nuclear magnetic resonance (NMR) analysis and high-resolution electrospray ionisation mass spectroscopy (HRESIMS). The new compound exhibited promising cytotoxicity against some cell lines derived from colorectal carcinoma, hepatic carcinoma and gastric carcinoma, indicating that compounds with trans-fused decalin system would be promising in the course of developing novel anticancer drugs.

Genome mining and biosynthesis of the Acyl-CoA:cholesterol acyltransferase inhibitor beauveriolide I and III in Cordyceps militaris.

Ascomycete fungi Cordyceps are widely used in traditional Chinese medicine, and numerous investigations have been carried out to uncover their biological activities. However, primary researches on the physiological effects of Cordyceps were committed using crude extracts. At present, there are only a few compounds which were comprehensively characterized from Cordyceps, partial owing to the low production. In order to scientifically take advantage of Cordyceps, we used the strategy of genome mining to discover bioactive compounds from Cordyceps militaris. We found the putative biosynthetic gene cluster of the acyl-CoA:cholesterol acyltransferase inhibitor beauveriolides in the genome of C. militaris, and produced the compounds by heterologous expression in Aspergillus nidulans. Production of beauveriolide I and III also was detected in both ferment mycelia and fruiting bodies of C. militaris. The possible biosynthetic pathway was proposed. Our studies unveil the active compounds of C. militaris against atherosclerosis and Alzheimer's disease and provide the enzyme resources for the biosynthesis of new cyclodepsipeptide molecules.