Positive feedback regulation of stgR expression for secondary metabolism in Streptomyces coelicolor.

LysR-type transcriptional regulators (LTTRs) compose a large family and are responsible for various physiological functions in bacteria, while little is understood about their regulatory mechanism on secondary metabolism in Streptomyces. Here we reported that StgR, a typical LTTR in Streptomyces coelicolor, was a negative regulator of undecylprodigiosin (Red) and γ-actinorhodin (Act) production in the early developmental phase of secondary metabolism by suppressing the expression of two pathway-specific regulator genes, redD and actII-orf4, respectively. Meanwhile, stgR expression was downregulated during secondary metabolism to remove its repressive effects on antibiotic production. Moreover, stgR expression was positively autoregulated by direct binding of StgR to its own promoter (stgRp), and the binding site adjacent to translation start codon was determined by a DNase I footprinting assay. Furthermore, the StgR-stgRp interaction could be destroyed by the antibiotic γ-actinorhodin produced from S. coelicolor. Thus, our results suggested a positive feedback regulatory mechanism of stgR expression and antibiotic production for the rapid and irreversible development of secondary metabolism in Streptomyces.

Genome shuffling improves thermotolerance and glutamic acid production of Corynebacteria glutamicum.

Genome shuffling was used to improve the thermotolerance of L: -glutamic acid-producing strain Corynebacteria glutamicum. Five strains with subtle improvements in high temperature tolerance and productivity were selected by ultraviolet irradiation and diethyl sulfate mutagenesis. An improved strain (F343) was obtained by three rounds of genome shuffling of the five strains as mentioned above. The cell density of F343 was four times higher than that of ancestor strains after 24 h of cultivation at 44°C, and importantly, the yield of L: -glutamic acid was increased by 1.8-times comparing with that of the ancestor strain at 38°C in a 5-L fermentor. With glucose supplement and two-stage pH control, the L: -glutamate acid concentration of F343 reached 119 g/L after fermentation for 30 h. The genetic diversity between F343 and its ancestors was also evaluated by amplified fragment length polymorphism analysis. Results suggest that the phenotypes for both thermotolerance and L: -glutamic acid production in F343 were evolved.

A potential antitumor drug (arginine deiminase) reengineered for efficient operation under physiological conditions.

Arginine deiminase (ADI, EC 3.5.3.6) is a potential antitumor drug for the treatment of arginine-auxotrophic tumors such as hepatocellular carcinomas (HCCs) and melanomas, and studies on human lymphatic leukemia cell lines have confirmed that ADI has antiangiogenic activity. Recent studies showed that a combination of taxane and ADI-PEG20, which induces caspase-independent apoptosis, is more effective than taxane monotherapy for prostate cancer. The main limitation of ADI from Pseudomonas plecoglossicida (PpADI) and of many other ADI enzymes lies in their pH-dependent activity profile. PpADI has a pH optimum at 6.5 and a pH shift from 6.5 to 7.5 results in an ∼80 % activity drop (the pH of human plasma is 7.35 to 7.45). In 2010, we reported a proof of concept for ADI engineering by directed evolution that resulted in variant M2 (K5T/D44E/H404R). M2 has a pH optimum of pH 7.0, a fourfold higher k(cat) value than the wild-type PpADI (pH 7.4, 0.5 M phosphate buffer), and an increased K(m) value for substrate arginine. In our latest work, variants M5 (K5T/D38H/D44E/A128T/H404R) and M6 (K5T/D38H/D44E/A128T/E296K/H404R) were generated by directed evolution by employing PBS buffer (pH 7.4), which mimics physiological conditions. The S(0.5) value of parent M3 (K5T/D44E/A128T/H404R) decreased from 2.01 to 1.48 mM (M5) and 0.81 mM (M6). The S(0.5) value of M6 (0.81 mM) is lower than that of wild-type PpADI (1.30 mM); the k(cat) values improved from 0.18 s(-1) (wild-type PpADI) to 17.56 s(-1) (M5, 97.6-fold) and 11.64 s(-1) (M6, 64.7-fold).

Succinic acid production from corn stover by simultaneous saccharification and fermentation using Actinobacillus succinogenes.

Simultaneous saccharification and fermentation (SSF) technique was applied for succinic acid production by Actinobacillus succinogenes in a 5-l stirred bioreactor with corn stover as the raw material. The process parameters of SSF, including corn stover pretreatment condition, substrate concentration, enzyme loading and fermentation temperature were investigated. Results indicated that pretreating corn stover with diluted alkaline was beneficial for the succinic acid production, and succinic acid yield could be significantly increased when adding the cellulase supplemented with cellobiase. The maximal succinic acid concentration and yield could reach 47.4 g/l and 0.72 g/g-substrate, respectively. The corresponding operation conditions were summarized as follows: SSF operation at 38 °C for 48 h, diluted alkaline pretreated corn stover as substrate with concentration of 70 g/l, enzyme loading of 20FPU cellulase and 10 U cellobiase per gram substrate. This result suggested an industrial potential of succinic acid production by using SSF and corn stover.

Directed evolution of an antitumor drug (arginine deiminase PpADI) for increased activity at physiological pH.

Arginine deiminase (ADI; EC 3.5.3.6) has been studied as a potential antitumor drug for the treatment of arginine-auxotrophic tumors, such as hepatocellular carcinomas (HCCs) and melanomas. Studies with human lymphatic leukemia cell lines confirmed that ADI is an antiangiogenic agent for treating leukemia. The main limitation of ADI from Pseudomonas plecoglossicida (PpADI) lies in its pH-dependent activity profile, its pH optimum is at 6.5. A pH shift from 6.5 to 7.5 results in an approximately 80 % drop in activity. (The pH of human plasma is 7.35 to 7.45.) In order to shift the PpADI pH optimum, a directed-evolution protocol based on an adapted citrulline-screening protocol in microtiter-plate format was developed and validated. A proof of concept for ADI engineering resulted in a pH optimum of pH 7.0 and increased resistance under physiological and slightly alkaline conditions. At pH 7.4, variant M2 (K5T/D44E/H404R) is four times faster than the wild-type PpADI and retains approximately 50 % of its activity relative to its pH optimum, compared to approximately 10 % in the case of the wild-type PpADI.

Fermentative production of succinic acid from straw hydrolysate by Actinobacillus succinogenes.

In this work, straw hydrolysates were used to produce succinic acid by Actinobacillus succinogenes CGMCC1593 for the first time. Results indicated that both glucose and xylose in the straw hydrolysates were utilized in succinic acid production, and the hydrolysates of corn straw was better than that of rice or wheat straw in anaerobic fermentation of succinic acid. However, cell growth and succinic acid production were inhibited when the initial concentration of sugar, which was from corn straw hydrolysate (CSH), was higher than 60 g l(-1). In batch fermentation, 45.5 g l(-1) succinic acid concentration and 80.7% yield were attained after 48 h incubation with 58 g l(-1) of initial sugar from corn straw hydrolysate in a 5-l stirred bioreactor. While in fed-batch fermentation, concentration of succinic acid achieved 53.2 g l(-1) at a rate of 1.21 g l(-1) h(-1) after 44 h of fermentation. Our work suggested that corn straw could be utilized for the economical production of succinic acid by A. succinogenes.

Arginine deiminase, a potential anti-tumor drug.

Arginine deiminase (ADI; EC 3.5.3.6), an arginine-degrading enzyme, has been studied as a potential anti-tumor drug for the treatment of arginine-auxotrophic tumors, such as hepatocellular carcinomas (HCCs) and melanomas. Studies with human lymphatic leukemia cell lines further suggest that ADI is a potential anti-angiogenic agent and is effective in the treatment of leukemia. For instance ADI-PEG-20, patented by Pheonix Pharmacologic Inc., is currently in clinical trials for the treatment of HCC (Phase II/III) and melanoma (Phase I/II). This review summarizes results on recombinant expression, structural analysis, PEG (polyethylene glycerol) modification, in vivo anti-cancer activities, and clinical studies of ADI. Discussions on heterogeneous expression of ADI, directed evolution for improving enzymatic properties, and HSA-fusion for increased in vivo activity conclude this review.

Economical succinic acid production from cane molasses by Actinobacillus succinogenes.

In this work, production of succinic acid by Actinobacillus succinogenes CGMCC1593 using cane molasses as a low cost carbon source was developed. In anaerobic bottles fermentation, succinic acid concentration of 50.6+/-0.9 g l(-1) was attained at 60 h using an optimum medium containing molasses pretreated with sulfuric acid, resulting in a succinic acid yield of 79.5+/-1.1% and sugar utilization of 97.1+/-0.6%. When batch fermentation was carried out in a 5-l stirred bioreactor with pretreated molasses, 46.4 g l(-1) of succinic acid was attained at 48 h and faster cells growth was also observed. Fed batch fermentation was performed to minimize the substrate (sugar) inhibition effect, giving 55.2 g l(-1) of succinic acid and 1.15 g l(-1)h(-1) of productivity at 48 h. The present study suggests that the inexpensive cane molasses could be utilized for the economical and efficient production of succinic acid by A. succinogenes.

History of the acetone-butanol-ethanol fermentation industry in China: development of continuous production technology.

The acetone-butanol-ethanol (ABE) fermentation industry in China was started in the early 1950s in Shanghai and expanded rapidly thereafter. At its peak, there were about 30 plants all over the country and the total annual production of solvents reached 170,000 tons. This large enterprise was compelled to complete shutdown at the end of the 20th century due to the rapid increase of petrochemicals. The success of the ABE industry in China had special features like the development of a continuous fermentation technology. Its main strategic considerations were as follows: maintaining maximal growth and acid production phase, adoption of multiple stages in the solvent phase to allow gradual adaptation to increasing solvent, and the incorporation of stillage to offer enough nutrients to delay cell degeneration. Due to the tremendous national demand for solvents, China has begun a new round of ABE fermentation research. It is expected that a new era in the ABE industry is on the horizon.

[Directed evolution of D-lactonohydrolase by error prone PCR and DNA shuffling].

D-lactonohydrolase is useful in the procedure of resolution of racemic pantolactone to produce D-pantolactone, but the activity and stability under low pH of the wild type enzyme is not satisfactory enough to be applied to industrial production. The expected properties of wild type enzyme were enhanced by directed evolution. According to the formation of products and pH indicators, a screening system was designed. After three sequential error prone PCR and one round DNA shuffling followed by screening, Mut E-861, the best mutant with improved activity and stability under low pH situation was obtained. Gene analysis of the Mut E-861 mutant indicated that the mutant enzyme had A352C, G721A mutations and a silent mutation of position 1038. Moreover, the activity and stability of Mut E-861 were determined. The results showed that the activity of this mutant was 5.5-fold higher than that of wild type, and the stability under low pH was improved at no expense of D-lactonohydrolase activity. After incubated at pH 6.0 and pH 5.0 the activity of D-lactonohydrolase could be retained 75% to 50%, however, compared with 40% to 20% for wild type.

[Studies on chemical constituents of Pinus armandii].

AIM: To study chemical constituents from pine cone of Pinus armandii Franch. METHODS: The constituents were isolated by chromatographic method and the structures were identified on the basis of spectral analysis. RESULTS: Four compounds were identified as 7-oxo-12alpha, 13beta-dihydroxyabiet-8(14)-en18-oic acid (I), 7-oxo-13beta-hydroxyabiet-8 (14)-en-18-oic acid (II), 8 (14)-podocarpen-13-on-18-oic acid (III) and lambertianic acid (IV). CONCLUSION: Compound I is a new diterpenoid and compounds II, III were isolated from this plant for the first time.

Biotransformation of isoeugenol to vanillin by a novel strain of Bacillus fusiformis.

A novel strain of Bacillus fusiformis, producing high amounts of vanillin from isoeugenol, was isolated from soil. Using 60% (v/v) isoeugenol as substrate and solvent and at pH 4.0, 37 degrees C and 180 rpm, vanillin was produced at 32.5 g l(-1) over 72 h. The unused isoeugenol was reusable.

[Cloning and expression of Fusarium moniliforme CGMCC 0536 D-lactonohydrolase gene in Escherichia coli].

The total cDNA obtained through reverse transcription of F. oxysporum CGMCC 0536 mRNA used as template, a fragment about 1.5kb was amplied with oligo(dT)15 primer and a gene specific primer designed on the base of the sequence of both NH2-terminus and the cDNA sequence encoding D-lactonohydrolase of Fusarium oxysporum reported on the NCBI, then the fragment was cloned to the pMD18-T vector and sequenced. The sequence encoding D-lactonohydrolase of F. moniliforme CGMCC 0536 shows a high homology of 90.06% with that of F. oxysporum indicating that the gene encoding D-lactonohydrolase is highly conservative. Two specific primers were designed according to the sequence result, and a fragment, 1146bp, was amplied using hot start PCR with these two specific primers. Subsequently, the resulting products were digested with EcoR I and Sal I and ligated to the pTrc99a vector digested with the same enzymes using T4 DNA ligase. the recombinant plasmid, pTrc99a-LAC, was transformed into Escherichia coli JM109. The two positive clones were induced with IPTG, and enzymes expressed in Escherichia coli JM109, the enzyme activity was about 37U and 41U respectively. The expression products were analyzed by SDS-polyacrylamide gel electrophoresis indicating that about 40kD protein was obtained.

[Studies on chemical constituents from pine cone of Pinus armandii].

OBJECTIVE: To study chemical constituents from pine cone of Pinus annandii. METHOD: The constituents were isolated by chromatographic method and the structures were identified on the basis of spectral analysis. RESULT: Seven compounds were identified as sandaracopimaric acid (I), isodextropimaric acid (II), 12-hydroxyabietic acid (III), dehydroabietic acid (IV), 15-hydroxydehydroabietic acid (V), beta-sitosterol (VI) and daucosterol (VII). CONCLUSION: Compounds I-IV were isolated from this plant for the first time.

Bioconversion of isoeugenol into vanillin by crude enzyme extracted from soybean.

Crude enzyme extracted from soybean was used to convert isoeugenol into vanillin. The effects of several factors on the bioconversion were studied. Conversion was affected by the amount of substrate and was also improved by the addition of absorbents, among which powdered activated carbon was the best. The effect of H2O2 concentration on the conversion was also studied. The optimum concentration of H2O2 was 1% (v/v). With 10 g/L of powdered activated carbon and 0.1% H2O2 added, vanillin reached a maximum concentration of 2.46 g/L after 36 h, corresponding to a molar yield of 13.3%.