Effects of two fillers and process conditions on the water treatment efficiency of a continuous packed bed biofilm reactor.

This study evaluated the treatment efficiency of two selected fillers and their combination for improving the water quality of aquaculture wastewater using a packed bed biofilm reactor (PBBR) under various process conditions. The fillers used were nanosheet (NS), activated carbon (AC), and a combination of both. The results indicated that the use of combined fillers and the hydraulic retention time (HRT) of 4 h significantly enhanced water quality in the PBBR. The removal rates of chemical oxygen demand, NO2-─N, total suspended solids（TSS）, and chlorophyll a were 63.55%, 74.25%, 62.75%, and 92.85%, respectively. The microbiota analysis revealed that the presence of NS increased the abundance of microbial phyla associated with nitrogen removal, such as Nitrospirae and Proteobacteria. The difference between the M1 and M2 communities was minimal. Additionally, the microbiota in different PBBR samples displayed similar preferences for carbon sources, and carbohydrates and amino acids were the most commonly utilized carbon sources by microbiota. These results indicated that the combination of NS and AC fillers in a PBBR effectively enhanced the treatment efficiency of aquaculture wastewater when operated at an HRT of 4 h. The findings provide valuable insights into optimizing the design of aquaculture wastewater treatment systems.

Remission of copper-induced liver injury through the PXR/NF-kB signaling pathway: The effects of dietary curcumin supplementation in largemouth bass (Micropterus salmoides).

The pregnane X receptor (PXR)/nuclear factor-kB (NF-kB) signaling pathway plays a critical role in regulating toxin-induced inflammation and apoptosis in mammals. Whether dietary curcumin (CUR) can prevent copper (Cu)-induced liver injury via this signaling pathway remains to be established in aquatic animals. Juvenile largemouth bass (Micropterus salmoides) were exposed to dietary Cu and CUR treatments for 8 weeks. The results showed that chronic Cu exposure induced oxidative stress, causing liver function damage and liver injury. Cu exposure stimulated inflammation by regulating nf-kb and pro-inflammatory genes such as tnfα and il-1ß and promoted apoptotic signals in the liver by modulating bcl2 and casp3 mRNA levels. In addition, Pearson correlation analysis verified that inflammatory and apoptotic responses were important indicators of Cu-induced liver injury. CUR attenuated stress responses by enhancing the antioxidant system. Importantly, CUR significantly stimulated PXR mRNA and protein levels in the Cu + CUR group and suppressed NF-κB activation to inhibit the inflammatory and apoptotic signaling cascade. These results suggest that CUR may be an effective activator of PXR in teleost fishes, exerting cytoprotective effects on Cu-induced liver injury via a PXR-mediated NF-κB repression mechanism. In conclusion, this study is the first to demonstrate that CUR may act as a potent PXR ligand that exerts hepatoprotective effects against Cu-induced liver injury. The findings shed light on the specific regulatory role of the PXR/NF-κB signaling pathway in liver pathogenesis and its potential as a therapeutic target in teleost fishes.

Hif1α/Dhrs3a Pathway Participates in Lipid Droplet Accumulation via Retinol and Ppar-γ in Fish Hepatocytes.

Excessive hepatic lipid accumulation is a common phenomenon in cultured fish; however, its underlying mechanisms are poorly understood. Lipid droplet (LD)-related proteins play vital roles in LD accumulation. Herein, using a zebrafish liver cell line (ZFL), we show that LD accumulation is accompanied by differential expression of seven LD-annotated genes, among which the expression of dehydrogenase/reductase (SDR family) member 3 a/b (dhrs3a/b) increased synchronously. RNAi-mediated knockdown of dhrs3a delayed LD accumulation and downregulated the mRNA expression of peroxisome proliferator-activated receptor gamma (pparg) in cells incubated with fatty acids. Notably, Dhrs3 catalyzed retinene to retinol, the content of which increased in LD-enriched cells. The addition of exogenous retinyl acetate maintained LD accumulation only in cells incubated in a lipid-rich medium. Correspondingly, exogenous retinyl acetate significantly increased pparg mRNA expression levels and altered the lipidome of the cells by increasing the phosphatidylcholine and triacylglycerol contents and decreasing the cardiolipin, phosphatidylinositol, and phosphatidylserine contents. Administration of LW6, an hypoxia-inducible factor 1α (HIF1α) inhibitor, reduced the size and number of LDs in ZFL cells and attenuated hif1αa, hif1αb, dhrs3a, and pparg mRNA expression levels. We propose that the Hif-1α/Dhrs3a pathway participates in LD accumulation in hepatocytes, which induces retinol formation and the Ppar-γ pathway.

Nitrated hydrochar reduce the Cd accumulation in rice and shift the microbial community in Cd contaminated soil.

Rice grown on Cd-contaminated soil may accumulate Cd in grain, which is extremely harmful to human health. Several managements are developed to reduce the Cd load in rice, while in-situ immobilization by soil amendments has been attractive for its feasibility. Waste-derived hydrochar (HC) has been shown effective at immobilizing Cd in soil. However, potential plant negative effects and huge application amount are crucial to resolving in extensive application of HC. Nitric acid ageing may be an effective method to deal with these problems. In this paper, HC and nitrated hydrochar (NHC) were added to the Cd-contaminated soil at rates of 1% and 2% in a rice-soil column experiment. Results showed that NHC markedly promoted root biomass of rice by 58.70-72.78%, whereas HC had effects of 35.86-47.57%. Notably, NHC at 1% reduced the accumulation of Cd in rice grain, root and straw by 28.04%, 15.08% and 11.07%, respectively. A consistent decrease of 36.30% in soil EXC-Cd concentration was caused by NHC-1%. Following soil microbial community was shifted greatly under HC and NHC applications. The relative abundance of Acidobacteria was decreased by 62.57% in NHC-2% and by 56.89% in HC-1%. Nevertheless, Proteobacteria and Firmicutes were promoted by NHC addition. In contrast to HC, co-occurrence network of dominated bacteria was more complex and centralized generated by NHC. Key bacteria in that metabolic network of NHC such as Anaerolineae and Archangiaceae played key roles in Cd immobilization. These observations verified that NHC was more efficient to decrease Cd accumulation in rice and could alleviate the negative roles to plant by microbial changings in community composition and network. It could provide an enrichment of paddy soil microbial responds to the interaction of NHC with Cd and lay a foundation for the remediation of Cd-contaminated soil by NHC.

The toxicokinetics and risk assessment of pyrethroids pesticide in tilapia (Oreochromis mossambicus) upon short-term water exposure.

Pyrethroids pesticides (PPs) are the widely adopted synthetic pesticides for agriculture and fishery. The frequent use of these pesticides leads to the accumulation of residues in the freshwater environments in China, subsequently affecting aquatic organisms and ecosystems. However, there are few reports on the toxicological and risk assessment of aquaculture aquatic products. In this study, the uptake, depuration kinetics and potential risk to human health and ecology of fenpropathrin, cypermethrin, fenvalerate, and deltamethrin were assessed using tilapia. The results indicated that four PPs were readily accumulated by tilapia. The bioconcentration factors (BCF) of the PPs in plasma and muscle were between 71.3 and 2112.1 L/kg and 23.9-295.3 L/kg, respectively. The half-lives (t1/2) of muscle and plasma were 2.90-9.20 d and 2.57-8.15 d. The risks of PPs residues in the muscle of tilapia and exposed water were evaluated by hazard quotient (HQ) and risk quotient (RQ). Although PPs residues in tilapia had a low dietary risk to human health, the residues in the exposed water had a high ecological risk to fish, daphnia, and green algae. Therefore, assessing the PPs content in freshwater aquaculture and monitoring their dosages and frequencies are highly necessitated to avoid their adverse effect on the aquaculture environment.

Facile Benzylic Alkylation of Arenes with Alcohols by Catalysis with Spirocyclic NHC IrIII Pincer Complex.

A facile benzylic alkylation of indenes and other arenes was developed from readily available primary and secondary alcohols using our newly investigated CCC pincer IrIII catalyst (SNIr-H). Excellent regioselectivity and yield (89 %) of the C3-alkylated indenes were obtained. Additionally, the challenging sp2 C-alkylation was readily accomplished. This method could be utilized for the synthesis of the analogs of a histamine H1 receptor antagonist and the functional material template molecule, indeno[2,1-a]indene. A hemilabile IrIII -dihydride intermediate was proposed based on control experiments and previous density functional theory (DFT) calculations for the borrowing hydrogen mechanism and is key to the success of this IrIII catalyst in the reduction of unactivated multi-substituted olefin intermediates.

Knockout of beta-2 microglobulin enhances cardiac repair by modulating exosome imprinting and inhibiting stem cell-induced immune rejection.

BACKGROUND AND AIMS: Allogeneic human umbilical mesenchymal stem cells (alloUMSC) are convenient cell source for stem cell-based therapy. However, immune rejection is a major obstacle for clinical application of alloUMSC for cardiac repair after myocardial infarction (MI). The immune rejection is due to the presence of human leukocyte antigen (HLA) class I molecule which is increased during MI. The aim of this study was to knockout HLA light chain ß2-microglobulin (B2M) in UMSC to enhance stem cell engraftment and survival after transplantation. METHODS AND RESULTS: We developed an innovative strategy using CRISPR/Cas9 to generate UMSC with B2M deletion (B2M-UMSC). AlloUMSC injection induced CD8+ T cell-mediated immune rejection in immune competent rats, whereas no CD8+ T cell-mediated killing against B2M-UMSC was observed even when the cells were treated with IFN-γ. Moreover, we demonstrate that UMSC-derived exosomes can inhibit cardiac fibrosis and restore cardiac function, and exosomes derived from B2M-UMSC are more efficient than those derived from UMSC, indicating that the beneficial effect of exosomes can be enhanced by modulating exosome's imprinting. Mechanistically, microRNA sequencing identifies miR-24 as a major component of the exosomes from B2M-UMSCs. Bioinformatics analysis identifies Bim as a putative target of miR-24. Loss-of-function studies at the cellular level and gain-of-function approaches in exosomes show that the beneficial effects of B2M-UMSCs are mediated by the exosome/miR-24/Bim pathway. CONCLUSION: Our findings demonstrate that modulation of exosome's imprinting via B2M knockout is an efficient strategy to prevent the immune rejection of alloUMSCs. This study paved the way to the development of new strategies for tissue repair and regeneration without the need for HLA matching.

Knockout of beta-2 microglobulin reduces stem cell-induced immune rejection and enhances ischaemic hindlimb repair via exosome/miR-24/Bim pathway.

Generating universal human umbilical mesenchymal stem cells (UMSCs) without immune rejection is desirable for clinical application. Here we developed an innovative strategy using CRISPR/Cas9 to generate B2M- UMSCs in which human leucocyte antigen (HLA) light chain ß2-microglobulin (B2M) was deleted. The therapeutic potential of B2M- UMSCs was examined in a mouse ischaemic hindlimb model. We show that B2M- UMSCs facilitated perfusion recovery and enhanced running capability, without inducing immune rejection. The beneficial effect was mediated by exosomes. Mechanistically, microRNA (miR) sequencing identified miR-24 as a major component of the exosomes originating from B2M- UMSCs. We identified Bim as a potential target of miR-24 through bioinformatics analysis, which was further confirmed by loss-of-function and gain-of-function approaches. Taken together, our data revealed that knockout of B2M is a convenient and efficient strategy to prevent UMSCs-induced immune rejection, and it provides a universal clinical-scale cell source for tissue repair and regeneration without the need for HLA matching in the future.

Structural Effect on Proton Conduction in Two Highly Stable Disubstituted Ferrocenyl Carboxylate Frameworks.

It is still a great challenge for people to obtain high proton conductive solid crystalline materials and accurately grasp their proton conduction mechanism. Herein, two highly stable disubstituted ferroceneyl carboxylate frameworks (DFCFs), {[HOOC(CH2)2OC]Fcc[CO(CH2)2COOH]} (DFCF 1) (Fcc = (η5-C5H4)Fe(η5-C5H4)) and [(HOOC)Fcc(COOH)] (DFCF 2) supported by intramolecular or intermolecular hydrogen bonds and π-π interactions were constructed and characterized by single crystal X-ray diffraction. Consequently, their water-assisted proton migration was researched systematically. As expected, 1 exhibited ultrahigh proton conductivity of 1.14 × 10-2 S·cm-1 at 373 K and 98% RH due to the presence of high-density free -COOH units. Unexpectedly, 2 displayed a low proton conductivity of 1.99 × 10-5 S·cm-1. On the basis of the analysis of crystal data, we believe that different arrangements of carboxyl groups lead to the different proton conductivity. Even more surprisingly, the proton conductivities of the two DFCFs are lower than those of their relevant monosubstituted ferroceneyl carboxylate frameworks (MFCFs), [FcCO(CH2)2COOH] (MFCF A) (Fc = (η5-C5H5)Fe(η5-C5H4)) (1.17 × 10-1 S·cm-1) and [FcCOOH] (MFCF B) (1.01 × 10-2 S·cm-1) under same conditions that were previously reported by us. This phenomenon indicates that the presence of a high number of free carboxyl groups in the framework does not necessarily cause high proton conductivity. We found that the arrangement of free carboxyl groups in the ferrocenyl framework plays a decisive role in proton conduction. This new discovery will provide guidance for the design of high proton conductive materials with free -COOH units.

Integrated microRNA and transcriptome profiling reveals a miRNA-mediated regulatory network of embryo abortion under calcium deficiency in peanut (Arachis hypogaea L.).

BACKGROUND: Peanut embryo development is a complex process involving a series of gene regulatory pathways and is easily affected by various elements in the soil. Calcium deficiency in the soil induces early embryo abortion in peanut, which provides an opportunity to determine the mechanism underlying this important event. MicroRNA (miRNA)-guided target gene regulation is vital to a wide variety of biological processes. However, whether miRNAs participate in peanut embryo abortion under calcium deficiency has yet to be explored. RESULTS: In this study, with the assistance of a recently established platform for genome sequences of wild peanut species, we analyzed small RNAs (sRNAs) in early peanut embryos. A total of 29 known and 132 potential novel miRNAs were discovered in 12 peanut-specific miRNA families. Among the identified miRNAs, 87 were differentially expressed during early embryo development under calcium deficiency and sufficiency conditions, and 117 target genes of the differentially expressed miRNAs were identified. Integrated analysis of miRNAs and transcriptome expression revealed 52 differentially expressed target genes of 20 miRNAs. The expression profiles for some differentially expressed targets by gene chip analysis were consistent with the transcriptome sequencing results. Together, our results demonstrate that seed/embryo development-related genes such as TCP3, AP2, EMB2750, and GRFs; cell division and proliferation-related genes such as HsfB4 and DIVARICATA; plant hormone signaling pathway-related genes such as CYP707A1 and CYP707A3, with which abscisic acid (ABA) is involved; and BR1, with which brassinosteroids (BRs) are involved, were actively modulated by miRNAs during early embryo development. CONCLUSIONS: Both a number of miRNAs and corresponding target genes likely playing key roles in the regulation of peanut embryo abortion under calcium deficiency were identified. These findings provide for the first time new insights into miRNA-mediated regulatory pathways involved in peanut embryo abortion under calcium deficiency.

Development of a temperature-responsive yeast cell factory using engineered Gal4 as a protein switch.

Conflict between cell growth and product accumulation is frequently encountered in biosynthesis of secondary metabolites. Herein, a temperature-dependent dynamic control strategy was developed by modifying the GAL regulation system to facilitate two-stage fermentation in yeast. A temperature-sensitive Gal4 mutant Gal4M9 was created by directed evolution, and used as a protein switch in ΔGAL80 yeast. After EGFP-reported validation of its temperature-responsive induction capability, the sensitivity and stringency of this system in multi-gene pathway regulation was tested, using lycopene as an example product. When Gal4M9 was used to control the expression of PGAL -driven pathway genes, growth and production was successfully decoupled upon temperature shift during fermentation, accumulating 44% higher biomass and 177% more lycopene than the control strain with wild-type Gal4. This is the first example of adopting temperature as an input signal for metabolic pathway regulation in yeast cell factories.

Combining Gal4p-mediated expression enhancement and directed evolution of isoprene synthase to improve isoprene production in Saccharomyces cerevisiae.

Current studies on microbial isoprene biosynthesis have mostly focused on regulation of the upstream mevalonic acid (MVA) or methyl-erythritol-4-phosphate (MEP) pathway. However, the downstream bottleneck restricting isoprene biosynthesis capacity caused by the weak expression and low activity of plant isoprene synthase (ISPS) under microbial fermentation conditions remains to be alleviated. Here, based on a previously constructed Saccharomyces cerevisiae strain with enhanced precursor supply, we strengthened the downstream pathway through increasing both the expression and activity of ISPS to further improve isoprene production. Firstly, a two-level expression enhancement system was developed for the PGAL1-controlled ISPS by overexpression of GAL 4. Meanwhile, the native GAL1/7/10 promoters were deleted to avoid competition for the transcriptional activator Gal4p, and GAL80 was disrupted to eliminate the dependency of gene expression on galactose induction. The IspS expression was obviously elevated upon enhanced Gal4p supply, and the isoprene production was improved from 6.0mg/L to 23.6mg/L in sealed-vial cultures with sucrose as carbon source. Subsequently, a novel high-throughput screening method was developed based on precursor toxicity and used for ISPS directed evolution towards enhanced catalytic activity. Combinatorial mutagenesis of the resulting ISPS mutants generated the best mutant ISPSM4, introduction of which into the GAL4-overexpressing strain YXM29 achieved 50.2mg/L of isoprene in sealed vials, and the isoprene production reached 640mg/L and 3.7g/L in aerobic batch and fed-batch fermentations, respectively. These results demonstrated the effectiveness of the proposed combinatorial engineering strategy in isoprene biosynthesis, which might also be feasible and instructive for biotechnological production of other valuable chemicals.

Combinatorial pathway optimization in Escherichia coli by directed co-evolution of rate-limiting enzymes and modular pathway engineering.

Metabolic engineering of microorganisms for heterologous biosynthesis is a promising route to sustainable chemical production which attracts increasing research and industrial interest. However, the efficiency of microbial biosynthesis is often restricted by insufficient activity of pathway enzymes and unbalanced utilization of metabolic intermediates. This work presents a combinatorial strategy integrating modification of multiple rate-limiting enzymes and modular pathway engineering to simultaneously improve intra- and inter-pathway balance, which might be applicable for a range of products, using isoprene as an example product. For intra-module engineering within the methylerythritol-phosphate (MEP) pathway, directed co-evolution of DXS/DXR/IDI was performed adopting a lycopene-indicated high-throughput screening method developed herein, leading to 60% improvement of isoprene production. In addition, inter-module engineering between the upstream MEP pathway and the downstream isoprene-forming pathway was conducted via promoter manipulation, which further increased isoprene production by 2.94-fold compared to the recombinant strain with solely protein engineering and 4.7-fold compared to the control strain containing wild-type enzymes. These results demonstrated the potential of pathway optimization in isoprene overproduction as well as the effectiveness of combining metabolic regulation and protein engineering in improvement of microbial biosynthesis. Biotechnol. Bioeng. 2016;113: 2661-2669. © 2016 Wiley Periodicals, Inc.

Sequential control of biosynthetic pathways for balanced utilization of metabolic intermediates in Saccharomyces cerevisiae.

Balanced utilization of metabolic intermediates and controllable expression of genes in biosynthetic pathways are key issues for the effective production of value-added chemicals in microbes. An inducer/repressor-free sequential control strategy regulated by glucose concentration in the growth environment was proposed to address these issues, and its efficiency was validated using heterologous beta-carotenoid biosynthesis in Saccharomyces cerevisiae as an example. Through sequential control of the downstream, upstream, and competitive pathways of farnesyl diphosphate (FPP), the crucial metabolic node in the biosynthesis of terpenoids, in a predetermined order, a carotenoid production of 1156 mg/L (20.79 mg/g DCW) was achieved by high-cell density fermentation. Quantitative PCR analysis of the regulated genes demonstrated that the transcription patterns were controlled in a sequential manner as expected. The inducer/repressor-free nature of this strategy offers a both practical and economically efficient approach to improved biosynthetic production of value-added chemicals.

Construction of lycopene-overproducing Saccharomyces cerevisiae by combining directed evolution and metabolic engineering.

Improved supply of farnesyl diphosphate (FPP) is often considered as a typical strategy for engineering Saccharomyces cerevisiae towards efficient terpenoid production. However, in the engineered strains with enhanced precursor supply, the production of the target metabolite is often impeded by insufficient capacity of the heterologous terpenoid pathways, which limits further conversion of FPP. Here, we tried to assemble an unimpeded biosynthesis pathway by combining directed evolution and metabolic engineering in S. cerevisiae for lycopene-overproduction. First, the catalytic ability of phytoene syntheses from different sources was investigated based on lycopene accumulation. Particularly, the lycopene cyclase function of the bifunctional enzyme CrtYB from Xanthophyllomyces dendrorhous was inactivated by deletion of functional domain and directed evolution to obtain mutants with solely phytoene synthase function. Coexpression of the resulting CrtYB11M mutant along with the CrtE and CrtI genes from X. dendrorhous, and the tHMG1 gene from S. cerevisiae led to production of 4.47 mg/g DCW (Dry cell weight) of lycopene and 25.66 mg/g DCW of the by-product squalene. To further increase the FPP competitiveness of the lycopene synthesis pathway, we tried to enhance the catalytic performance of CrtE by directed evolution and created a series of pathway variants by varying the copy number of Crt genes. Finally, fed-batch fermentation was conducted for the diploid strain YXWPD-14 resulting in accumulation of 1.61 g/L (24.41 mg/g DCW) of lycopene, meanwhile, the by-production of squalene was reduced to below 1 mg/g DCW.

Identification and elimination of metabolic bottlenecks in the quinone modification pathway for enhanced coenzyme Q10 production in Rhodobacter sphaeroides.

In this report, UbiE and UbiH in the quinone modification pathway (QMP) were identified in addition to UbiG as bottleneck enzymes in the CoQ10 biosynthesis by Rhodobacter sphaeroides. The CoQ10 content was enhanced after co-overexpression of UbiE and UbiG, however, accompanied by the accumulation of the intermediate 10P-MMBQ. UbiH was then co-overexpressed to pull the metabolic flux towards downstream, resulting in an elevated CoQ10 productivity and decreased biomass. On the other hand, the expression levels of UbiE and UbiG were tuned to eliminate the intermediate accumulation, however at the sacrifice of productivity. To alleviate the detrimental effect on either productivity or cell growth, we tried to fuse UbiG with UbiE and localize them onto the membrane to elevate intermediate conversion. By fusing UbiE and UbiG to pufX, CoQ10 was accumulated to 108.51±2.76mg/L with a biomass of 12.2±0.9g/L. At last, we combined the optimized QMP and the previously engineered 2-methyl-d-erythritol-4-phosphate pathway (MEP) to further boost CoQ10 biosynthesis, resulting in a strain with 138±2.64mg/L CoQ10 production.

Highly efficient biosynthesis of astaxanthin in Saccharomyces cerevisiae by integration and tuning of algal crtZ and bkt.

Astaxanthin is a highly valued carotenoid with strong antioxidant activity and has wide applications in aquaculture, food, cosmetic, and pharmaceutical industries. The market demand for natural astaxanthin promotes research in metabolic engineering of heterologous hosts for astaxanthin production. In this study, an astaxanthin-producing Saccharomyces cerevisiae strain was created by successively introducing the Haematococcus pluvialis ß-carotenoid hydroxylase (crtZ) and ketolase (bkt) genes into a previously constructed ß-carotene hyperproducer. Further integration of strategies including codon optimization, gene copy number adjustment, and iron cofactor supplementation led to significant increase in the astaxanthin production, reaching up to 4.7 mg/g DCW in the shake-flask cultures which is the highest astaxanthin content in S. cerevisiae reported to date. Besides, the substrate specificity of H. pluvialis CrtZ and BKT and the probable formation route of astaxanthin from ß-carotene in S. cerevisiae were figured out by expressing the genes separately and in combination. The yeast strains engineered in this work provide a basis for further improving biotechnological production of astaxanthin and might offer a useful general approach to the construction of heterologous biosynthetic pathways for other natural products.

Enhanced production of coenzyme Q10 by self-regulating the engineered MEP pathway in Rhodobacter sphaeroides.

Fine-tuning the expression level of an engineered pathway is crucial for the metabolic engineering of a host toward a desired phenotype. However, most engineered hosts suffer from nonfunctional protein expression, metabolic imbalance, cellular burden or toxicity from intermediates when an engineered pathway is first introduced, which can decrease production of the desired product. To circumvent these obstacles, we developed a self-regulation system utilizing the trc/tac promoter, LacI(q) protein and ribosomal binding sites (RBS). With the purpose of improving coenzyme Q10 (CoQ10 ) production by increasing the decaprenyl diphosphate supplement, enzymes DXS, DXR, IDI, and IspD were constitutively overexpressed under the control of the trc promoter in Rhodobacter sphaeroides. Then, a self-regulation system combining a set of RBSs for adjusting the expression of the LacI(q) protein was applied to tune the expression of the four genes, resulting in improved CoQ10 production. Finally, another copy of the tac promoter with the UbiG gene (involved in the ubiquinone pathway of CoQ10 biosynthesis) was introduced into the engineered pathway. By optimizing the expression level of both the upstream and downstream pathway, CoQ10 production in the mutants was improved up to 93.34 mg/L (7.16 mg/g DCW), about twofold of the wild-type (48.25 mg/L, 3.24 mg/g DCW).

Construction of a controllable ß-carotene biosynthetic pathway by decentralized assembly strategy in Saccharomyces cerevisiae.

Saccharomyces cerevisiae is an important platform organism for the synthesis of a great number of natural products. However, the assembly of controllable and genetically stable heterogeneous biosynthetic pathways in S. cerevisiae still remains a significant challenge. Here, we present a strategy for reconstructing controllable multi-gene pathways by employing the GAL regulatory system. A set of marker recyclable integrative plasmids (pMRI) was designed for decentralized assembly of pathways. As proof-of-principle, a controllable ß-carotene biosynthesis pathway (∼16 kb) was reconstructed and optimized by repeatedly using GAL10-GAL1 bidirectional promoters with high efficiency (80-100%). By controling the switch time of the pathway, production of 11 mg/g DCW of total carotenoids (72.57 mg/L) and 7.41 mg/g DCW of ß-carotene was achieved in shake-flask culture. In addition, the engineered yeast strain exhibited high genetic stability after 20 generations of subculture. The results demonstrated a controllable and genetically stable biosynthetic pathway capable of increasing the yield of target products. Furthermore, the strategy presented in this study could be extended to construct other pathways in S. cerevisisae.

Enhanced activity of Rhizomucor miehei lipase by deglycosylation of its propeptide in Pichia pastoris.

Many studies have demonstrated that the properties of enzymes expressed in eukaryotes can be affected by the position and extent of glycosylation on enzyme. In this study, two potential glycosylation sites (the 8th and the 58th asparagine) were identified and the effect of propeptide glycosylation on Rhizomucor miehei lipase (RML) expressed in Pichia pastoris was investigated. To better understand the effect of glycosylation on the activity of RML, three mutants (M1, generated by N8A; M2, generated by N58A; and M3, generated by N8A and N58A) were designed to generate deglycosylated enzymes. The results showed that deglycosylated RML exhibited a twofold higher activity compared to the wild type. However, it was also found that glycosylation on the propeptide was important for the removal of the propeptide by Kex2 protease and secretion of the enzyme. Thus, our study provided a further understanding into the role of glycosylation on enzyme function.