Unravelling and engineering an operon involved in the side-chain degradation of sterols in Mycolicibacterium neoaurum for the production of steroid synthons

BACKGROUND

Harnessing engineered Mycolicibacteria to convert cheap phytosterols into valuable steroid synthons is a basic way in the industry for the production of steroid hormones. Thus, C-19 and C-22 steroids are the two main types of commercial synthons and the products of C17 side chain degradation of phytosterols. During the conversion process of sterols, C-19 and C-22 steroids are often produced together, although one may be the main product and the other a minor byproduct. This is a major drawback of the engineered Mycolicibacteria for industrial application, which could be attributed to the co-existence of androstene-4-ene-3,17-dione (AD) and 22-hydroxy-23,24-bisnorchol-4-ene-3-one (HBC) sub-pathways in the degradation of the sterol C17 side chain. Since the key mechanism underlying the HBC sub-pathway has not yet been clarified, the above shortcoming has not been resolved so far.

RESULTS

The key gene involved in the putative HBC sub-pathway was excavated from the genome of M. neoaurum by comparative genomic analysis. Interestingly, an aldolase- encoding gene, atf1, was identified to be responsible for the first reaction of the HBC sub-pathway, and it exists as a conserved operon along with a DUF35-type gene chsH4, a reductase gene chsE6, and a transcriptional regulation gene kstR3 in the genome. Subsequently, atf1 and chsH4 were identified as the key genes involved in the HBC sub-pathway. Therefore, an updated strategy was proposed to develop engineered C-19 or C-22 steroid-producing strains by simultaneously modifying the AD and HBC sub-pathways. Taking the development of 4-HBC and 9-OHAD-producing strains as examples, the improved 4-HBC-producing strain achieved a 20.7 g/L production titer with a 92.5% molar yield and a 56.4% reduction in byproducts, and the improved 9-OHAD producing strain achieved a 19.87 g/L production titer with a 94.6% molar yield and a 43.7% reduction in byproduct production.

CONCLUSIONS

The excellent performances of these strains demonstrated that the primary operon involved in the HBC sub-pathway improves the industrial strains in the conversion of phytosterols to steroid synthons.

Improved cryptic plasmids in probiotic Escherichia coli Nissle 1917 for antibiotic-free pathway engineering

The engineered probiotic Escherichia coli Nissle 1917 (EcN) is expected to be employed in the diagnosis and treatment of various diseases. However, the introduced plasmids typically require antibiotics to maintain genetic stability, and the cryptic plasmids in EcN are usually eliminated to avoid plasmid incompatibility which may change the inherent probiotic characteristics. Here, we provided a simple design to minimize the genetic change of probiotics by eliminating native plasmids and reintroducing the recombinants carrying functional genes. Specific insertion sites in the vectors showed significant differences in the expression of fluorescence proteins. Selected integration sites were applied in the de novo synthesis of salicylic acid, leading to a titer of 142.0 ± 6.0 mg/L in a shake flask with good production stability. Additionally, the design successfully realized the biosynthesis of ergothioneine (45 mg/L) by one-step construction. This work expands the application scope of native cryptic plasmids to the easy construction of functional pathways. KEY POINTS: • Cryptic plasmids of EcN were designed to express exogenous genes • Insertion sites with different expression intensities in cryptic plasmids were provided • Target products were stably produced by engineering cryptic plasmids.

Driving the conversion of phytosterol to 9α-hydroxy-4-androstene-3,17-dione in Mycolicibacterium neoaurum by engineering the supply and regeneration of flavin adenine dinucleotide

BACKGROUND

The conversion of phytosterols to steroid synthons by engineered Mycolicibacteria comprises one of the core steps in the commercial production of steroid hormones. This is a complex oxidative catabolic process, and taking the production of androstenones as example, it requires about 10 equivalent flavin adenine dinucleotide (FAD). As the high demand for FAD, the insufficient supply of FAD may be a common issue limiting the conversion process.

RESULTS

We substantiated, using the production of 9α-hydroxy-4-androstene-3,17-dione (9-OHAD) as a model, that increasing intracellular FAD supply could effectively increase the conversion of phytosterols into 9-OHAD. Overexpressing ribB and ribC, two key genes involving in FAD synthesis, could significantly enhance the amount of intracellular FAD by 167.4% and the production of 9-OHAD by 25.6%. Subsequently, styrene monooxygenase NfStyA2B from Nocardia farcinica was employed to promote the cyclic regeneration of FAD by coupling the oxidation of nicotinamide adenine dinucleotide (NADH) to NAD⁺, and the production of 9-OHAD was further enhanced by 9.4%. However, the viable cell numbers decreased by 20.1%, which was attributed to sharply increased levels of H₂O₂ because of the regeneration of FAD from FADH₂. Thus, we tried to resolve the conflict between FAD regeneration and cell growth by the overexpression of catalase and promotor replacement. Finally, a robust strain NF-P2 was obtained, which could produce 9.02 g/L 9-OHAD after adding 15 g/L phytosterols with productivity of 0.075 g/(L h), which was 66.7% higher than that produced by the original strain.

CONCLUSIONS

This study highlighted that the cofactor engineering, including the supply and recycling of FAD and NAD⁺ in Mycolicibacterium, should be adopted as a parallel strategy with pathway engineering to improve the productivity of the industrial strains in the conversion of phytosterols into steroid synthons.

Boosting the epoxidation of squalene to produce triterpenoids in Saccharomyces cerevisiae

BACKGROUND

Polycyclic triterpenoids (PTs) are common in plants, and have attracted considerable interest due to their remarkable biological activities. Currently, engineering the ergosterol synthesis pathway in Saccharomyces cerevisiae is a safe and cost-competitive way to produce triterpenoids. However, the strict regulation of ERG1 involved in the epoxidation of squalene limits the triterpenoid production.

RESULTS

In this study, we found that the decrease in ERG7 protein level could dramatically boost the epoxidation of squalene by improving the protein stability of ERG1. We next explored the potential factors that affected the degradation process of ERG1 and confirmed that ERG7 was involved in the degradation process of ERG1. Subsequently, expression of four different triterpene cyclases utilizing either 2,3-oxidosqualene or 2,3:22,23-dioxidosqualene as the substrate in ERG7-degraded strains showed that the degradation of ERG7 to prompt the epoxidation of squalene could significantly increase triterpenoid production. To better display the potential of the strategy, we increased the supply of 2,3-oxidosqualene, optimized flux distribution between ergosterol synthesis pathway and β-amyrin synthesis pathway, and modified the GAL-regulation system to separate the growth stage from the production stage. The best-performing strain ultimately produced 4216.6 ± 68.4 mg/L of β-amyrin in a two-stage fed-fermentation (a 47-fold improvement over the initial strain).

CONCLUSIONS

This study showed that deregulation of the native restriction in ergosterol pathway was an effective strategy to increase triterpenoid production in yeast, which provided a new insight into triterpenoids biosynthesis.

Enhancing the Activity of an Alcohol Dehydrogenase by Using "Aromatic Residue Scanning" at Potential Plasticity Sites

An alcohol dehydrogenase LkADH was successfully engineered to exhibit improved activity and substrate tolerance for the production of (S)-2-chloro-1-(3,4-difluorophenyl)ethanol, an important precursor of ticagrelor. Five potential hotspots were identified for enzyme mutagenesis by using natural residue abundance as an indicator to evaluate their potential plasticity. A semi-rational strategy named "aromatic residue scanning" was applied to randomly mutate these five sites simultaneously by using tyrosine, tryptophan, and phenylalanine as "exploratory residues" to introduce steric hindrance or potential π-π interactions. The best variant Lk-S96Y/L199W identified with 17.2-fold improvement in catalytic efficiency could completely reduce up to 600 g/L (3.1 M) 2-chloro-1-(3,4-difluorophenyl)ethenone in 12 h with >99.5 % ee, giving the highest space-time yield ever reported. This study, therefore, offers a strategy for mutating alcohol dehydrogenase to reduce aromatic substrates and provides an efficient variant for the efficient synthesis of (S)-2-chloro-1-(3,4-difluorophenyl)ethanol.

Engineering Escherichia coli for l-homoserine production

l-homoserine, a nonprotein amino acid, is used to synthesize many active substances in the industry. Here, to develop a robust l-homoserine-producing strain, Escherichia coli W3110 was used as a chassis to be engineered. Based on a previous construct with blocked competing routes for l-homoserine synthesis, five genes were overexpressed by promoter replacement strategy to increase the l-homoserine production, including enhancement of precursors for l-homoserine synthesis (ppc, thrA, and asd), reinforcement of the NADPH supply (pntAB) and efflux transporters (rhtA) to improve the l-homoserine production. However, the plasmid losing was to blame for the wildly fluctuating fermentation performance of engineered strains, ranging between 2.1 and 6.2 g/L. Then, a hok/sok toxin/antitoxin system was introduced into the free plasmid expression cassette to maintain the genetic stability of the episomal plasmid; consequently, the plasmid-losing rate sharply decreased, resulting in the engineered strain SHL17, which exhibited excellent stability in l-homoserine production, with 6.3 g/L in shake flasks and 44.4 g/L in a 5-L fermenter without antibiotic addition. This work verified the effective use of the hok/sok toxin/antitoxin system combined with promoter engineering to improve the genetic stability of E. coli episomal plasmids without antibiotics.

Structure-guided engineering of a flavin-containing monooxygenase for the efficient production of indirubin

Indirubin is a bisindole compound for the treatment of chronic myelocytic leukemia. Here, we presented a structure-guided method to improve the activity of a flavin-containing monooxygenase (bFMO) for the efficient production of indirubin in Escherichia coli. A flexible loop interlocked with the active pocket through a helix and the substrate tunnel rather than the active pocket in bFMO were identified to be two reconfigurable structures to improve its activity, resulting in K223R and N291T mutants with enhanced catalytic activity by 2.5- and 2.0-fold, respectively. A combined modification at the two regions (K223R/D317S) achieved a 6.6-fold improvement in catalytic efficiency (kcat/Km) due to enhancing π-π stacking interactions stabilization. Finally, an engineered E. coli strain was constructed by metabolic engineering, which could produce 860.7 mg/L (18 mg/L/h) indirubin, the highest yield ever reported. This work provides new insight into the redesign of FMOs to boost their activities and an efficient approach to produce indirubin.

Multiplexed site-specific genome engineering in Mycolicibacterium neoaurum by Att/Int system

Genomic integration of genes and pathway-sized DNA cassettes is often an indispensable way to construct robust and productive microbial cell factories. For some uncommon microbial hosts, such as Mycolicibacterium and Mycobacterium species, however, it is a challenge. Here, we present a multiplexed integrase-assisted site-specific recombination (miSSR) method to precisely and iteratively integrate genes/pathways with controllable copies in the chromosomes of Mycolicibacteria for the purpose of developing cell factories. First, a single-step multi-copy integration method was established in M. neoaurum by a combination application of mycobacteriophage L5 integrase and two-step allelic exchange strategy, the efficiencies of which were ∼100% for no more than three-copy integration events and decreased sharply to ∼20% for five-copy integration events. Second, the R4, Bxb1 and ΦC31 bacteriophage Att/Int systems were selected to extend the available integration toolbox for multiplexed gene integration events. Third, a reconstructed mycolicibacterial Xer recombinases (Xer-cise) system was employed to recycle the selection marker of gene recombination to facilitate the iterative gene manipulation. As a proof of concept, the biosynthetic pathway of ergothioneine (EGT) in Mycolicibacterium neoaurum ATCC 25795 was achieved by remodeling its metabolic pathway with a miSSR system. With six copies of the biosynthetic gene clusters (BGCs) of EGT and pentose phosphate isomerase (PRT), the titer of EGT in the resulting strain in a 30 mL shake flask within 5 days was enhanced to 66 mg/L, which was 3.77 times of that in the wild strain. The improvements indicated that the miSSR system was an effective, flexible, and convenient tool to engineer the genomes of Mycolicibacteria as well as other strains in the Mycobacteriaceae due to their proximate evolutionary relationships.

CRISPR-Cas Assisted Shotgun Mutagenesis Method for Evolutionary Genome Engineering

Genome mutagenesis drives the evolution of organisms. Here, we developed a CRISPR-Cas assisted random mutation (CARM) technique for whole-genome mutagenesis. The method leverages an entirely random gRNA library and SpCas9-NG to randomly damage genomes in a controllable shotgunlike manner that then triggers diverse and abundant mutations via low-fidelity repair. As a proof of principle, CARM was applied to evolve the capacity of Saccharomyces cerevisiae BY4741 to produce β-carotene. After seven rounds of iterative evolution over two months, a β-carotene hyperproducing strain, C7-143, was isolated with a 10.5-fold increase in β-carotene production and 857 diverse genomic mutations that comprised indels, duplications, inversions, and chromosomal rearrangements. Transcriptomic analysis revealed that the expression of 2541 genes of strain C7-143 was significantly altered, suggesting that the metabolic landscape of the strain was deeply reconstructed. In addition, CARM was applied to evolve industrially relevant S. cerevisiae CEN.PK2-1C for S-adenosyl-L-methionine production, which was increased 2.28 times after just one round. Thus, CARM can contribute to increasing genetic diversity to identify new phenotypes that could further be investigated by reverse engineering.

One-pot biosynthesis of 7β-hydroxyandrost-4-ene-3,17-dione from phytosterols by cofactor regeneration system in engineered mycolicibacterium neoaurum

Background

7β-hydroxylated steroids (7β-OHSt) possess significant activities in anti-inflammatory and neuroprotection, and some of them have been widely used in clinics. However, the production of 7β-OHSt is still a challenge due to the lack of cheap 7β-hydroxy precursor and the difficulty in regio- and stereo-selectively hydroxylation at the inert C7 site of steroids in industry. The conversion of phytosterols by Mycolicibacterium species to the commercial precursor, androst-4-ene-3,17-dione (AD), is one of the basic ways to produce different steroids. This study presents a way to produce a basic 7β-hydroxy precursor, 7β-hydroxyandrost-4-ene-3,17-dione (7β-OH-AD) in Mycolicibacterium, for 7β-OHSt synthesis.

Results

A mutant of P450-BM3, mP450-BM3, was mutated and engineered into an AD producing strain for the efficient production of 7β-OH-AD. The enzyme activity of mP450-BM3 was then increased by 1.38 times through protein engineering and the yield of 7β-OH-AD was increased from 34.24 mg L^− 1 to 66.25 mg L^− 1. To further enhance the performance of 7β-OH-AD producing strain, the regeneration of nicotinamide adenine dinucleotide phosphate (NADPH) for the activity of mP450-BM3-0 was optimized by introducing an NAD kinase (NADK) and a glucose-6-phosphate dehydrogenase (G6PDH). Finally, the engineered strain could produce 164.52 mg L^− 1 7β-OH-AD in the cofactor recycling and regeneration system.

Conclusions

This was the first report on the one-pot biosynthesis of 7β-OH-AD from the conversion of cheap phytosterols by an engineered microorganism, and the yield was significantly increased through the mutation of mP450-BM3 combined with overexpression of NADK and G6PDH. The present strategy may be developed as a basic industrial pathway for the commercial production of high value products from cheap raw materials.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-022-01786-5.

Engineering Saccharomyces cerevisiae for Hyperproduction of β-Amyrin by Mitigating the Inhibition Effect of Squalene on β-Amyrin Synthase

The study aims to enhance β-amyrin production in Saccharomyces cerevisiae by peroxisome compartmentalization. First, overaccumulated squalene was determined as a key limiting factor for the production of β-amyrin since it could inhibit the activity of β-amyrin synthase GgbAs1. Second, to mitigate the inhibition effect, the enhanced squalene synthesis pathway was compartmentalized into peroxisomes to insulate overaccumulated squalene from GgbAs1, and thus the specific titer of β-amyrin reached 57.8 mg/g dry cell weight (DCW), which was 2.6-fold higher than that of the cytosol engineering strain. Third, by combining peroxisome compartmentalization with the "push-pull-restrain" strategy (ERG1 and GgbAs1 overexpression and ERG7 weakening), the production of β-amyrin was further increased to 81.0 mg/g DCW (347.0 mg/L). Finally, through fed-batch fermentation in a 5 L fermenter, the titer of β-amyrin reached 2.6 g/L, which is the highest reported to date. The study provides a new perspective to engineering yeasts as a platform for triterpene production.

Improving the biotransformation efficiency of soybean phytosterols in Mycolicibacterium neoaurum by the combined deletion of fbpC3 and embC in cell envelope synthesis

Biotransformation of soybean phytosterols into 9α-hydroxy-4-androstene-3,17-dione (9-OHAD) by mycobacteria is the core step in the synthesis of adrenocortical hormone. However, the low permeability of the dense cell envelope largely inhibits the overall conversion efficiency of phytosterols. The antigen 85 (Ag85) complex encoded by fbpA, fbpB, and fbpC was proposed as the key factor in the combined catalysis of mycoloyl for producing mycolyl-arabinogalactan (m-AG) and trehalose dimycolate (TDM) in mycobacterial cell envelope. Herein, we confirmed that fbpC3 was essential for the biotransformation of trehalose monomycolate (TMM) to TDM in Mycolicibacterium neoaurum. The deficiency of this gene raised the cell permeability, thereby enhancing the steroid uptake and utilization. The 9-OHAD yield in the fbpC3-deficient 9-OHAD-producing strain was increased by 21.3%. Moreover, the combined deletion of fbpC3 and embC further increased the 9-OHAD yield compared to the single deletion of fbpC3. Finally, after 96 h of bioconversion in industrial resting cells, the 9-OHAD yield of 11.2 g/L was achieved from 20 g/L phytosterols and the productivity reached 0.116 g/L/h. In summary, this study suggested the critical role of the fbpC3 gene in the synthesis of TDM in M. neoaurum and verified the feasibility of improving the bioconversion efficiency of phytosterols through the cell envelope engineering strategy.

Metabolic compartmentalization in yeast mitochondria: Burden and solution for squalene overproduction

Harnessing mitochondria is considered as a promising method for biosynthesis of terpenes due to the adequate supply of acetyl-CoA and redox equivalents in mitochondria. However, mitochondrial engineering often causes serious metabolic burden indicated by poor cell growth. Here, we systematically analyzed the metabolic burden caused by the compartmentalization of the MVA pathway in yeast mitochondria for squalene synthesis. The phosphorylated intermediates of the MVA pathway, especially mevalonate-5-P and mevalonate-5-PP, conferred serious toxicity within mitochondria, which significantly compromised its possible advantages for squalene synthesis and was difficult to be significantly improved by routine pathway optimization. These phosphorylated intermediates were converted into ATP analogues, which strongly inhibited ATP-related cell function, such as mitochondrial oxidative respiration. Fortunately, the introduction of a partial MVA pathway from acetyl-CoA to mevalonate in mitochondria as well as the augmentation of the synthesis of mevalonate in cytosol could significantly promote the growth of yeasts. Accordingly, a combinatorial strategy of cytoplasmic and mitochondrial engineering was proposed to alleviate the metabolic burden caused by the compartmentalized MVA pathway in mitochondria and improve cell growth. The strategy also displayed the superimposed effect of cytoplasmic engineering and mitochondrial engineering on squalene production. Through a two-stage fermentation process, the squalene titer reached 21.1 g/L with a specific squalene titer of 437.1 mg/g dcw, which was the highest at present. This provides new insight into the production of squalene and other terpenes in yeasts based on the advantages of mitochondrial engineering.

CRISPR-Cas12a assisted precise genome editing of Mycolicibacterium neoaurum

Efficient and convenient genetic manipulation of mycobacteria, important microorganisms in human healthcare and the pharmaceutical industry, is limited. In this study, using a model strain Mycolicibacterium neoaurum ATCC 25795, the classical bacterium for the production of valuable steroidal pharmaceuticals, a genome editing system employing CRISPR-Cas12a to achieve efficient and precise genetic manipulation has been developed. Targeted genome mutations could be easily achieved by the CRISPR-Cas12a system without exogenous donor templates, assisted by innate non-homologous end-joining (NHEJ). CRISPR-Cas12a enabled rapid one-step genomic DNA fragment deletions of 1 kb, 5 kb, 10 kb, 15 kb, 20 kb and 24 kb with efficiencies of 70 %, 30 %, 30 %, 20 %, 20 % and 10 %, respectively. Combined with the pNIL/pGOAL system, CRISPR-Cas12a successfully integrated the gene of interest into the targeted genomic site by single crossover and double crossovers with efficiencies of 100 % and 9 %, respectively, using a two-plasmid system. The robust CRISPR systems developed demonstrated strong potential for precise genome editing in M. neoaurum, including targeted deletion of DNA sequences of various lengths and integration of targeted genes into desired sites in the genome.

High-Level Production of Sesquiterpene Patchoulol in Saccharomyces cerevisiae

Patchoulol is a tricyclic sesquiterpene widely used in perfumes and cosmetics. Herein, comprehensive engineering strategies were employed to construct an efficient yeast strain for patchoulol production. First, a platform strain was constructed via pathway modification. Second, three off-pathway genes were deleted, which led to significant physiological changes in yeast. Further, strengthening of the ergosterol pathway, enhancement of the energy supply, and a decrease in intracellular reactive oxygen species were implemented to improve the physiological status of yeast, demonstrating a new promotive relationship between ergosterol biosynthesis and synthesis of patchoulol. Moreover, patchoulol synthase was improved through protein modification and Mg²⁺ addition, reaching a final titer of 141.5 mg/L in a shake flask. Finally, a two-stage fermentation with dodecane addition was employed to achieve the highest production (1632.0 mg/L, 87.0 mg/g dry cell weight, 233.1 mg/L/d) ever reported for patchoulol in a 5 L bioreactor. This work lays a foundation for green and efficient patchoulol production.

Functional expression of a novel methanol-stable esterase from Geobacillus subterraneus DSM13552 for biocatalytic synthesis of cinnamyl acetate in a solvent-free system

BACKGROUND

Esterases are widely distributed in nature and have important applications in medical, industrial and physiological. Recently, the increased demand for flavor esters has prompted the search of catalysts like lipases and esterases. Esterases from thermophiles also show thermal stability at elevated temperatures and have become enzymes of special interest in biotechnological applications. Although most of esterases catalyzed reactions are carried out in toxic and inflammable organic solvents, the solvent-free system owning many advantages such as low cost and easy downstream processing.

RESULTS

The gene estGSU753 from Geobacillus subterraneus DSM13552 was cloned, sequenced and overexpressed into Escherichia coli BL21 (DE3). The novel gene has an open reading frame of 753 bp and encodes 250-amino-acid esterase (EstGSU753). The sequence analysis showed that the protein contains a catalytic triad formed by Ser97, Asp196 and His226, and the Ser of the active site is located in the conserved motif Gly95-X-Ser97-X-Gly99 included in most esterases and lipases. The protein catalyzed the hydrolysis of pNP-esters of different acyl chain lengths, and the enzyme specific activity was 70 U/mg with the optimum substrate pNP-caprylate. The optimum pH and temperature of the recombinant enzyme were 8.0 and 60 °C respectively. The resulting EstGSU753 showed remarkable stability against methanol. After the incubation at 50% methanol for 9 days, EstGSU753 retained 50% of its original activity. Even incubation at 90% methanol for 35 h, EstGSU753 retained 50% of its original activity. Also, the preliminary study of the transesterification shows the potential value in synthesis of short-chain flavor esters in a solvent-free system, and more than 99% conversion was obtained in 6 h (substrate: cinnamyl alcohol, 1.0 M).

CONCLUSIONS

This is the first report of esterase gene cloning from Geobacillus subterraneus with detailed enzymatic properties. This methanol-stable esterase showed potential value in industrial applications especially in the perfume industry.

Enhancing the bioconversion of phytosterols to steroidal intermediates by the deficiency of kasB in the cell wall synthesis of Mycobacterium neoaurum

Background

The bioconversion of phytosterols into high value-added steroidal intermediates, including the 9α-hydroxy-4-androstene-3,17-dione (9-OHAD) and 22-hydroxy-23,24-bisnorchol-4-ene-3-one (4-HBC), is the cornerstone in steroid pharmaceutical industry. However, the low transportation efficiency of hydrophobic substrates into mycobacterial cells severely limits the transformation. In this study, a robust and stable modification of the cell wall in M. neoaurum strain strikingly enhanced the cell permeability for the high production of steroids.

Results

The deletion of the nonessential kasB, encoding a β-ketoacyl-acyl carrier protein synthase, led to a disturbed proportion of mycolic acids (MAs), which is one of the most important components in the cell wall of Mycobacterium neoaurum ATCC 25795. The determination of cell permeability displayed about two times improvement in the kasB-deficient strain than that of the wild type M. neoaurum. Thus, the deficiency of kasB in the 9-OHAD-producing strain resulted in a significant increase of 137.7% in the yield of 9α-hydroxy-4-androstene-3,17-dione (9-OHAD). Ultimately, the 9-OHAD productivity in an industrial used resting cell system was reached 0.1135 g/L/h (10.9 g/L 9-OHAD from 20 g/L phytosterol) and the conversion time was shortened by 33%. In addition, a similar self-enhancement effect (34.5%) was realized in the 22-hydroxy-23,24-bisnorchol-4-ene-3-one (4-HBC) producing strain.

Conclusions

The modification of kasB resulted in a meaningful change in the cell wall mycolic acids. Deletion of the kasB gene remarkably improved the cell permeability, leading to a self-enhancement of the steroidal intermediate conversion. The results showed a high efficiency and feasibility of this construction strategy.

Metabolic Engineering of Saccharomyces cerevisiae To Overproduce Squalene

Squalene has wide applications in the food and pharmaceutical industries. Engineering microbes to produce squalene is a promising alternative for traditional production approaches. In this study, squalene production was enhanced to 978.24 mg/L through stepwise overexpression of the enzymes that catalyze acetyl-CoA to squalene. Subsequently, to increase the activity of HMG-CoA reductase and alleviate the high dependence on NADPH, the HMG-CoA reductase (NADH-HMGR) from Silicibacter pomeroyi, highly specific for NADH, was introduced, which increased squalene production to 1086.31 mg/L. Native ethanol dehydrogenase ADH2 and acetaldehyde dehydrogenase ADA from Dickeya zeae were further overexpressed, which enhanced the capability to utilize ethanol for squalene synthesis and endowed the engineered strain with greater adaptability to high ethanol concentrations. Finally, a remarkable squalene production of 9472 mg/L was obtained from ethanol via carbon source-controlled fed-batch fermentation. This study will greatly accelerate the process of developing microbial cell factories for squalene production.

Immediate, multiplexed and sequential genome engineering facilitated by CRISPR/Cas9 in Saccharomyces cerevisiae

A method called Cas-3P allowing for immediate, multiplexed and sequential genome engineering was developed using one plasmid expressing Cas9 and three marked plasmid backbones (P1, P2 and P3) for guide RNA (gRNA) expression. The three marked gRNA plasmid backbones were recurred in a P1-P2-P3 order for sequential gene targeting, without construction of any additional plasmid and elimination of gRNA plasmid by induction in each round. The efficiency of direct gRNA plasmid curing mediated by Cas-3P was more than 40% in sequential gene targeting. Besides, Cas-3P allowed single-, double- and triple-loci gene targeting with an efficiency of 75%, 36.8% and 8.2% within 3-4 days, respectively. Through three sequential rounds of gene targeting within 10 days, S. cerevisiae was optimized for the production of patchoulol by replacing one promoter, overexpressing three genes and disrupting four genes. The work is important for practical application in the cell factory engineering of S. cerevisiae.

Preparation and purification of novel phosphatidyl prodrug and performance modulation of phosphatidyl nanoprodrug

Background

A novel phosphatidyl nanoprodrug system can be selectively released parent drugs in cancer cells, triggered by the local overexpression of phospholipase D (PLD). This system significantly reduces the intrinsic disadvantages of conventional chemotherapeutic drugs. However, the separation and purification processes of phosphatidyl prodrug, the precursor of phosphatidyl nanoprodrug, have not been established, and the preparation of nanocrystals with good stability and tumor-targeting capability is still challenging.

Results

In this study, we established a successive elution procedure for the phosphatidyl prodrug—phosphatidyl mitoxantrone (PMA), using an initial ten-bed volume of chloroform/methanol/glacial acetic acid/water (26/10/0.8/0.7) (v/v/v/v) followed by a five-bed volume (26/10/0.8/3), with which purity rates of 96.93% and overall yields of 50.35% of PMA were obtained. Moreover, to reduce the intrinsic disadvantages of conventional chemotherapeutic drugs, phosphatidyl nanoprodrug—PMA nanoprodrug (NP@PMA)—was prepared. To enhance their stability, nanoparticles were modified with polyethylene glycol (PEG). We found that nanoprodrugs modified by PEG (NP@PEG–PMA) were stably present in RPMI-1640 medium containing 10% FBS, compared with unmodified nanoprodrug (NP@PMA). To enhance active tumor-targeting efficiency, we modified nanoparticles with an arginine-glycine-aspartic acid (RGD) peptide (NP@RGD–PEG–PMA). In vitro cytotoxicity assays showed that, compared with the cytotoxicity of NP@PEG–PMA against tumor cells, that of NP@RGD–PEG–PMA was enhanced. Thus, RGD modification may serve to enhance the active tumor-targeting efficiency of a nanoprodrug, thereby increasing its cytotoxicity.

Conclusions

A process for the preparation and purification of novel phosphatidyl prodrugs was successfully established, and the nanoprodrug was modified using PEG for enhanced nanoparticle stability, and using RGD peptide for enhanced active tumor-targeting efficiency. These procedures offer considerable potential in the development of functional antitumor prodrugs.

Significantly Enhanced Production of Patchoulol in Metabolically Engineered Saccharomyces cerevisiae

Patchoulol, a natural sesquiterpene compound, is widely used in perfumes and cosmetics. Several strategies were adopted to enhance patchoulol production in Saccharomyces cerevisiae: (i) farnesyl pyrophosphate (FPP) synthase and patchoulol synthase were fused to increase the utilization of FPP precursor; (ii) expression of the limiting genes of the mevalonate pathway was enhanced; (iii) squalene synthase was weakened by a glucose-inducible promoter of HXT1 (promoter for hexose transporter) to reduce metabolic flux from FPP to ergosterol; and (iv) farnesol biosynthesis was inhibited to decrease the consumption of FPP. Glucose was used to balance the trade-off between the competitive squalene and patchoulol pathways. The patchoulol production was 59.2 ± 0.7 mg/L in a shaken flask with a final production of 466.8 ± 12.3 mg/L (20.5 ± 0.5 mg/g dry cell weight) combined with fermentation optimization, which was 7.8-fold higher than the reported maximum production. The work significantly promoted the industrialization process of patchoulol production using biobased microbial platforms.

Enhanced conversion of sterols to steroid synthons by augmenting the peptidoglycan synthesis gene pbpB in Mycobacterium neoaurum

Some species of mycobacteria have been modified to transform sterols to valuable steroid synthons. The unique cell wall of mycobacteria has been recognized as an important organelle to absorb sterols. Some cell wall inhibitors (e.g., vancomycin and glycine) have been validated to enhance sterol conversion by interfering with transpeptidation in peptidoglycan biosynthesis. Therefore, two transpeptidase genes, pbpA and pbpB, were selected to rationally modify the cell wall to simulate the enhancement effect of vancomycin and glycine on sterol conversion in a 22-hydroxy-23,24-bisnorchol-4-ene-3-one (4-HBC) producing strain (WIII). Unexpectedly, the pbpA or pbpB gene augmentation was conducive to the utilization of sterols. The pbpB augmentation strain WIII-pbpB was further investigated for its better performance. Compared to WIII, the morphology of WIII-pbpB was markedly changed from oval to spindle, indicating alterations of the cell wall. Biochemical analysis indicated that the altered cell wall properties of WIII-pbpB might contribute to the positive effect on sterol utilization. The productivity of 4-HBC was enhanced by 28% in the WIII-pbpB strain compared to that of WIII. These results demonstrated that the modification of peptidoglycan synthesis can improve the conversion of sterols to steroid synthons in mycobacteria.

Metabolic Adaptation of Mycobacterium neoaurum ATCC 25795 in the Catabolism of Sterols for Producing Important Steroid Intermediates

To understand the adaptation of Mycobacterium neoaurum ATCC25795 ( Mn) in sterol catabolism and steroid production, we used integrated transcriptome and proteome analysis to identify the biochemical pathways utilized in this process. Metabolic alterations during sterol catabolism center on propionyl-CoA pools. Generally, enhanced pathways for metabolizing propionyl-CoA were found in Mn, which were tightly coordinated with cell-envelope biosynthesis. The cells responded to sterol substrates and toxic steroid products by changing the composition of the cell envelope. This adaptive mechanism allowed Mn to use minimally water-soluble sterol as a carbon source. Several putative efflux proteins were found to be induced in Mn. They probably transported products to the extracellular environment, protecting the cells against high intracellular levels of toxic intermediates, inhibition of which also influenced sterol uptake. The work provided various targets for rational engineering of robust Mn with powerful sterol-uptake capacity and strong tolerance to toxic products for the steroid industry.

CRISPR/Cpf1 facilitated large fragment deletion in Saccharomyces cerevisiae

In this study, we focused on the applicability of CRISPR/Cpf1 in genome simplification of Saccharomyces cerevisiae and established a CRISPR/Cpf1 assisted method for rapid markerless large fragment deletion to facilitate laboratory evolution of geome of S. cerevisiae by rational genetic engineering. This method uses a Cpf1 expression plasmid and a crRNA array expression plasmid. The DNA fragment between two DSBs generated by CRISPR/Cpf1 can be cut off from the chromosome, along with re-ligation of the genomic endpoints of the DSBs. Using this method, the large DNA fragment of ∼38 kb between the two genes of TRM10 and REX4 was successfully and rapidly deleted, which was verified by PCR and Sanger DNA Sequencing. This method is simple and rapid, and can be easily implemented for large fragment deletion in S. cerevisiae.

Integrated Transcriptome and Proteome Studies Reveal the Underlying Mechanisms for Sterol Catabolism and Steroid Production in Mycobacterium neoaurum

Integrated transcriptome and proteome studies were performed to investigate sterol biotransformation in wild-type Mycobacterium neoaurum ATCC 25795 ( Mn) and the mutant strains producing steroid intermediates. Transcriptome and proteome studies indicated that several metabolic activities were noticeably dynamic, including cholesterol degradation, central carbon metabolism, cell envelope biosynthesis, glycerol metabolism, and transport. Interestingly, a poor overall correlation between mRNA and translation profiles was found, which might contribute to the metabolic adaptation in cholesterol catabolism. A gene cluster covering 111 genes was discovered to encode for cholesterol catabolism in Mn. Generally, transcription and/or translation of the genes in KstR1 regulon was upregulated, and the induction of genes in KstR2 regulon was not as significant as that of KstR1 regulon. Several induced genes showing potential roles for cholesterol catabolism were found. Further identification of these genes and investigation of the correlation among key metabolic activities could help for the development of efficient steroid-producing strains.

Cpf1-assisted efficient genomic integration of in vivo assembled DNA parts in Saccharomyces cerevisiae

OBJECTIVES

To test the applicability of Cpf1 from Francisella novivida in genomic integration of in vivo assembled DNA parts in Saccharomyces cerevisiae.

RESULTS

An easy-to-use vector toolkit, containing a CEN6/ARS4 plasmid expressing Cpf1 from Francisella novivida (FnCpf1) and a 2 μ plasmid for crRNA or crRNA array expressing, was constructed for Cpf1-assisted genomic integration in S. cerevisiae. Our results showed that FnCpf1 allowed for targeted singleplex, doubleplex, and tripleplex genomic integration of in vivo assembled DNA parts with efficiencies of 95, 52, and 43%, respectively.

CONCLUSIONS

CRISPR-Cpf1 system allows for efficient genomic integration of in vivo assembled DNA parts in S. cerevisiae, and thus provides an alternative CRISPR-Cas method for metabolic pathway engineering in addition to CRISPR-Cas9 system previously reported for yeast.

Enhancement of 9α-Hydroxy-4-androstene-3,17-dione Production from Soybean Phytosterols by Deficiency of a Regulated Intramembrane Proteolysis Metalloprotease in Mycobacterium neoaurum

Modification of the sterol catabolism pathway in mycobacteria may result in the accumulation of some valuable steroid pharmaceutical intermediates, such as 9α-hydroxy-4-androstene-3,17-dione (9-OHAD). In previous work, sigma factor D (SigD) was identified as a negative factor of the 9-OHAD production in Mycobacterium neoaurum. Here, the deficiency of rip1 putatively coding for a regulated intramembrane proteolysis metalloprotease (Rip1), which could cleave the negative regulator of SigD (anti-SigD), enhanced the transcription of some key genes (choM1, kshA, and hsd4A) in the sterol catabolic pathway. Furthermore, the deletion of rip1 increased the consumption of phytosterols by 37.8% after 96 h of growth in M. neoaurum. The production of 9-OHAD in the engineered M. neoaurumΔkstD1ΔkstD2ΔkstD3Δrip1 (MnΔk123Δrip1) strain was ultimately increased by 27.3% compared to that in its parental strain M. neoaurumΔkstD1ΔkstD2ΔkstD3 (MnΔk123). This study further confirms the important role of SigD-related factors in the catabolism of sterols.

Primers and copper responsive promoter design and data of real-time RT-PCR assay in filamentous fungus Trichoderma reesei

This data article contains data related to the research article entitled “Copper-mediated on-off control of gene expression in filamentous fungus Trichoderma reesei” (Wang et al., 2017) [1]. Four kinds of copper responsive promoters were designed. Quantitative PCR (qPCR) was performed to determine relative mRNA levels of red fluorescent protein gene (rfp) extracted from cells grown under different concentrations of CuSO₄. Three deletion vectors were constructed by using a copper-mediated self-excision cassette instead of a xylose-mediated self-excision cassette (Zhang et al., 2016) [2] to knock out xyn1, one of the two major specific endo-β-1,4-xylanases (Rauscher et al., 2006) [3], xyr1, the key transcriptional activator of cellulolytic and xylanolytic genes (Lichius et al., 2015) [4], and ace3, a factor essential for cellulase production (Häkkinen et al., 2014) [5]. This data article reports the primers, vector construction, and qPCR assay.

Improving the production of 22-hydroxy-23,24-bisnorchol-4-ene-3-one from sterols in Mycobacterium neoaurum by increasing cell permeability and modifying multiple genes

Background

The strategy of modifying the sterol catabolism pathway in mycobacteria has been adopted to produce steroidal pharmaceutical intermediates, such as 22-hydroxy-23,24-bisnorchol-4-ene-3-one (4-HBC), which is used to synthesize various steroids in the industry. However, the productivity is not desirable due to some inherent problems, including the unsatisfactory uptake rate and the low metabolic efficiency of sterols. The compact cell envelope of mycobacteria is a main barrier for the uptake of sterols. In this study, a combined strategy of improving the cell envelope permeability as well as the intracellular sterol metabolism efficiency was investigated to increase the productivity of 4-HBC.

Results

MmpL3, encoding a transmembrane transporter of trehalose monomycolate, is an important gene influencing the assembly of mycobacterial cell envelope. The disruption of mmpL3 in Mycobacterium neoaurum ATCC 25795 significantly enhanced the cell permeability by 23.4% and the consumption capacity of sterols by 15.6%. Therefore, the inactivation of mmpL3 was performed in a 4-HBC-producing strain derived from the wild type M. neoaurum and the 4-HBC production in the engineered strain was increased by 24.7%. Subsequently, to enhance the metabolic efficiency of sterols, four key genes, choM1, choM2, cyp125, and fadA5, involved in the sterol conversion pathway were individually overexpressed in the engineered mmpL3-deficient strain. The production of 4-HBC displayed the increases of 18.5, 8.9, 14.5, and 12.1%, respectively. Then, the more efficient genes (choM1, cyp125, and fadA5) were co-overexpressed in the engineered mmpL3-deficient strain, and the productivity of 4-HBC was ultimately increased by 20.3% (0.0633 g/L/h, 7.59 g/L 4-HBC from 20 g/L phytosterol) compared with its original productivity (0.0526 g/L/h, 6.31 g/L 4-HBC from 20 g/L phytosterol) in an industrial resting cell bio-transformation system.

Conclusions

Increasing cell permeability combined with the co-overexpression of the key genes (cyp125, choM1, and fadA5) involved in the conversion pathway of sterol to 4-HBC was effective to enhance the productivity of 4-HBC. The strategy might also be useful for the conversion of sterol to other steroidal intermediates by mycobacteria.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-017-0705-x) contains supplementary material, which is available to authorized users.

Role Identification and Application of SigD in the Transformation of Soybean Phytosterol to 9α-Hydroxy-4-androstene-3,17-dione in Mycobacterium neoaurum

9α-Hydroxy-4-androstene-3,17-dione (9-OHAD) is a valuable steroid pharmaceutical intermediate which can be produced by the conversion of soybean phytosterols in mycobacteria. However, the unsatisfactory productivity and conversion efficiency of engineered mycobacterial strains hinder their industrial applications. Here, a sigma factor D (sigD) was investigated due to its dramatic downregulation during the conversion of phytosterols to 9-OHAD. It was determined as a negative regulator in the metabolism of phytosterols, and the deletion of sigD in a 9-OHAD-producing strain significantly enhanced the titer of 9-OHAD by 18.9%. Furthermore, a high yielding strain was constructed by the combined modifications of sigD and choM2, a key gene in the phytosterol metabolism pathway. After the modifications, the productivity of 9-OHAD reached 0.071 g/L/h (10.27 g/L from 20 g/L phytosterol), which was 22.5% higher than the original productivity of 0.058 g/L/h (8.37 g/L from 20 g/L phytosterol) in the industrial resting cell biotransformation system.

[Up-regulation of ErbB3-binding protein 1 inhibits the growth of esophageal carcinoma cells]

The objective of this study was to investigate the role of ErbB3-binding protein 1 (Ebp1) in the growth of esophageal squamous cell carcinoma (ESCC) cells and the underlying mechanism. Eca109 and KYSE150 cells were transfected with lentiviral vector carrying Ebp1 gene. The mRNA levels of Ebp1 in esophageal cancer tissues and paired adjacent normal tissues were examined by real-time PCR. The growth and viability of esophageal carcinoma cells were assessed using MTT and crystal violet assays, respectively. Clone-forming abilities of Eca109 and KYSE150 cells were analyzed by soft agar assay. Apoptotic rates of esophageal carcinoma cells were detected by flow cytometry, and expression levels of the proteins involved in apoptosis were assessed by Western blot. Tumorigenicity of Eca109 cells were detected by nude mouse transplantation tumor experiment. The results indicated that the mRNA levels of Ebp1 in esophageal cancer tissues was down-regulated compared with paired adjacent normal tissues. The growth and viability of Eca109 and KYSE150 cells were all suppressed by Ebp1 overexpression. Besides, Ebp1 overexpression induced apoptosis, increased Rb and P53 expressions, and decreased CyclinD1 expression in Eca109 and KYSE150 cells. In addition, Ebp1 overexpression inhibited the tumorigenesis of Eca109 cells in vivo. These results suggest that Ebp1 may suppress the growth of esophageal carcinoma cells in vitro and in vivo by inducing apoptosis.

RNA-Seq analysis uncovers non-coding small RNA system of Mycobacterium neoaurum in the metabolism of sterols to accumulate steroid intermediates

BACKGROUND

Understanding the metabolic mechanism of sterols to produce valuable steroid intermediates in mycobacterium by a noncoding small RNA (sRNA) view is still limited. In the work, RNA-seq was implemented to investigate the noncoding transcriptome of Mycobacterium neoaurum (Mn) in the transformation process of sterols to valuable steroid intermediates, including 9α-hydroxy-4-androstene-3,17-dione (9OHAD), 1,4-androstadiene-3,17-dione (ADD), and 22-hydroxy-23, 24-bisnorchola-1,4-dien-3-one (1,4-BNA).

RESULTS

A total of 263 sRNA candidates were predicted from the intergenic regions in Mn. Differential expression of sRNA candidates was explored in the wide type Mn with vs without sterol addition, and the steroid intermediate producing Mn strains vs wide type Mn with sterol addition, respectively. Generally, sRNA candidates were differentially expressed in various strains, but there were still some shared candidates with outstandingly upregulated or downregulated expression in these steroid producing strains. Accordingly, four regulatory networks were constructed to reveal the direct and/or indirect interactions between sRNA candidates and their target genes in four groups, including wide type Mn with vs without sterol addition, 9OHAD, ADD, and BNA producing strains vs wide type Mn with sterol addition, respectively. Based on these constructed networks, several highly focused sRNA candidates were discovered to be prevalent in the networks, which showed comprehensive regulatory roles in various cellular processes, including lipid transport and metabolism, amino acid transport and metabolism, signal transduction, cell envelope biosynthesis and ATP synthesis. To explore the functional role of sRNA candidates in Mn cells, we manipulated the overexpression of candidates 131 and 138 in strain Mn-9OHAD, which led to enhanced production of 9OHAD from 1.5- to 2.3-fold during 6 d' fermentation and a slight effect on growth rate.

CONCLUSIONS

This study revealed the complex and important regulatory roles of noncoding small RNAs in the metabolism of sterols to produce steroid intermediates in Mn, further analysis of which will promote the better understanding about the molecular metabolism of these sRNA candidates and open a broad range of opportunities in the field.

A novel cold-adapted type I pullulanase of Paenibacillus polymyxa Nws-pp2: in vivo functional expression and biochemical characterization of glucans hydrolyzates analysis

Background

Pullulanase is an important debranching enzyme and has been widely utilized to hydrolyse the α-1,6 glucosidic linkages in starch/sugar industry. Selecting new bacterial strains or improving bacterial strains is a prerequisite and effective solution in industrial applications. Although many pullulanase genes have been cloned and sequenced, there is no report of P. polymyxa type I pullulanase gene or the recombinant strain. Meanwhile most of the type I pullulanase investigated exhibit thermophilic or mesophilic properties. There are just few reports of cold-adapted pullulanases, which have optimum activity at moderate temperature and exhibit rather high catalytic activity at cold. Previously, six strains showing distinct pullulan degradation ability were isolated using enrichment procedures. As containing novel bacterium resource and significant pullulanase activity, strain Nws-pp2 was selected for in-depth study.

Methods

In this study, a type I pullulanase gene (pulN) was obtained from the strain P. polymyxa Nws-pp2 by degenerate primers. Through optimization of induced conditions, the recombinant PulN achieved functional soluble expression by low temperature induction. The enzyme characterizations including the enzyme activity/stability, optimum temperature, optimum pH and substrate specificity were also described through protein purification.

Results

The pullulanase gene (named pulN), encoding a novel cold-adapted type I pullulanase (named Pul_N), was obtained from isolated strain Paenibacillus polymyxa Nws-pp2. The gene had an open reading frame of 2532-bp and was functionally expressed in Escherichia coli through optimization of induced conditions. The level of functional Pul_N-like protein reached the maximum after induction for 16 h at 20 °C and reached about 0.34 mg/ml (about 20 % of total protein) with an activity of 6.49 U/ml. The purified recombinant enzyme with an apparent molecular mass of about 96 kDa was able to attack specifically the α-1,6 linkages in pullulan to generate maltotriose as the major product. The purified Pul_N showed optimal activity at pH 6.0 and 35 °C, and retained more than 40 % of the maximum activity at 10 °C (showing cold-adapted). The pullulanase activity was significantly enhanced by Co²⁺ and Mn²⁺, meanwhile Cu²⁺ and SDS inhibited pullulanase activity completely. The Km and Vmax values of purified Pul_N were 15.25 mg/ml and 20.1 U/mg, respectively. The Pul_N hydrolyzed pullulan, amylopectin, starch, and glycogen, but not amylose. Substrate specificity and products analysis proved that the purified pullulanase from Paenibacillus polymyxa Nws-pp2 belong to a type I pullulanase.

Conclusions

This report of the novel type I pullulanase in Paenibacillus polymyxa would contribute to pullulanase research from Paenibacillus spp. significantly. Also, the cold-adapted pullulanase produced in recombinant strain shows the potential application.

Electronic supplementary material

The online version of this article (doi:10.1186/s12896-015-0215-z) contains supplementary material, which is available to authorized users.

Influence of temperature on nucleus degradation of 4-androstene-3, 17-dione in phytosterol biotransformation by Mycobacterium sp

One of the steroid intermediates, 4-androstene-3, 17-dione (AD), in the biotransformation of phytosterols is valuable for the production of steroid medicaments. However, its degradation during the conversion process is one of the main obstacles to obtain high yields. In this study, the effect of temperature on nucleus degradation during microbial biotransformation of phytosterol was investigated. The results indicated that microbial degradation of phytosterol followed the AD-ADD-'9-OH-ADD' pathway, and that two important reactions involved in nucleus degradation, conversions of AD to ADD and ADD to 9-OH-ADD, were inhibited at 37°C. With a change in the culture temperature from 30 to 37°C, nucleus degradation was reduced from 39·9% to 17·6%, due to inhibition of the putative KstD and Ksh. These results suggested a simple way to decrease the nucleus degradation in phytosterol biotransformation and a new perspective on the possibilities of modifying the metabolism of strains used in industrial applications.

SIGNIFICANCE AND IMPACT OF THE STUDY

Nucleus degradation of products is one of the main problems encountered during phytosterol biotransformation. To solve this problem, the effect of temperature on nucleus degradation was investigated in the industrial production of steroid intermediates. The results are also helpful to the genetic modification of sterol-producing strains.

Light-mediated control of gene expression in filamentous fungus Trichoderma reesei

We developed a light-mediated system based on synthetic light-switchable transactivators. The transactivators bind promoter upon blue-light exposure and rapidly initiate transcription of target transgenes in filamentous fungus Trichoderma reesei. Light is inexpensive to apply, easily delivered, and instantly removed, and thus has significant advantages over chemical inducers.

Improving Gluconobacter oxydans performance in the in situ removal of the inhibitor for asymmetric resolution of racemic 1-phenyl-1,2-ethanediol

Gluconobacter oxydans DSM2003 was used to catalyze the oxidation of racemic 1-phenyl-1,2-ethanediol (PED) for the production of (S)-enantiomer. The oxidative product mandelic acid produced strong inhibition to this reaction and largely reduced the activity of biocatalyst, which was the key problem in the reaction. In order to overcome this bottleneck, an anion exchange resin was selected and introduced as adsorbent for the in situ removal of the inhibitor from the reaction system. This method increased the substrate concentration from 12 to 60 g/L and the yield of (S)-PED by approximately five times from 4.9 g/L, on the premise that the enantiomeric excess (ee) value of (S)-PED remained above 96% and the reaction time was no more than 20 h. Moreover, the final space-time yield was over 1.2g/L/h, which was higher than that reported from previous studies.

Inhibition of Liver Cancer Cell Proliferation and Migration by a Combination of (-)-Epigallocatechin-3- Gallate and Ascorbic Acid

A mixture of (-)-epigallocatechin-3-gallate (EGCG) and ascorbic acid exhibited 73.2% inhibition of SMMC-7721 cell proliferation in a soft agar colony formation assay, which was much higher than EGCG (40.4%) or ascorbic acid (12.4%) alone. In the cell migration assay, the mixture also significantly suppressed the migration of SMMC-7721 cells by 65.9% while EGCG and/or ascorbic acid did by 28.9% and 18.7%, respectively. Ascorbic acid was able to enhance the antioxidant activity of EGCG by decreasing the intracellular oxidative stress according to fluorographic analysis of oxidative stress. In conclusion, the combination of EGCG and ascorbic acid can strongly suppress the proliferation and metastasis of liver cancer cells, possibly with a mechanism associated with the scavenging of reactive oxygen species. All these events add to our knowledge of liver cancer chemotherapy.

In VitroandIn VivoReversal of Cancer Cell Multidrug Resistance by 2',4'-Dihydroxy-6'-methoxy-3',5'- dimethylchalcone

2',4'-Dihydroxy-6'-methoxy-3',5'-dimethylchalcone (DMC) isolated from the buds of Cleistocalyx operculatus, was investigated for its reversal effects on cancer cell multidrug resistance. DMC potentiated the cytotoxicity of the chemotherapeutic agent doxorubicin to drug-resistant KB-A1 cells. When 5 microM DMC was present simultaneously with doxorubicin, the IC50 of DOX on KB-A1 cells decreased from 13.9 +/- 0.7 microg/ml to 3.6 +/- 0.7 microg/ml. A human carcinoma xenograft model was established with the KB-A1 cell line. DMC could sensitize the tumors to doxorubicin as indicated by a considerable reduction in tumor weight. DMC increased the intracellular accumulation of doxorubicin in KB-A1 cells. When KB-A1 cells were exposed to 10 microg/ml doxorubicin combined with 5, 10, 20 microM DMC for 4 hours, the intracellular concentrations of doxorubicin were increased 1.4-, 1.8-, 3.1-fold, respectively, in comparison with doxorubicin alone treatment. All results indicated that DMC had reversal effects on the multidrug resistance phenotype.

Identification of Petriella setifera LH and characterization of its crude carboxymethyl cellulase for application in denim biostoning

The phylogenetic tree of the partial elongation factor-1 alpha gene fits better than the partial 18S rDNA for generic classification. From the results of the molecular tree and analysis of morphological characters, Petriella setifera LH was identified. It can be induced to produce carboxymethyl cellulase (CMCase). The crude CMCase only shows a 44.1-kDa band by activity staining after SDS-PAGE. It is optimally active at 55°C and pH 6.0, and is stable from pH 5.0-8.0 and at 45°C or below. The crude CMCase, which is not affected by Co(2+), is strongly activated in the presence of 10 mM Na(+), K(+), Ca(2+), Mg(2+), EDTA, and Mn(2+). It is strongly inhibited by 10 mM Fe(2+), Pb(2+), Al(3+), Zn(2+), Ag(+), Fe(3+), and Cu(2+). When compared with denim treatment by Novoprime A800 (a commercial neutral cellulase), crude CMCase exhibits a similar fabric weight loss and indigo dye removal. These results indicate that crude CMCase has potential application in denim biostoning.