Fermentation optimization and enzyme characterization of a new ι-Carrageenase from Pseudoalteromonas carrageenovora ASY5

Background: A new ι-carrageenase-producing strain was screened from mangroves and authenticated as Pseudoalteromonas carrageenovora ASY5 in our laboratory. The potential application of this new strain was evaluated. Results: Medium compositions and culturing conditions in shaking flask fermentation were firstly optimized by single-factor experiment. ι-Carrageenase activity increased from 0.34 U/mL to 1.08 U/mL after test optimization. Optimal fermentation conditions were 20°C, pH 7.0, incubation time of 40 h, 15 g/L NaCl, 1.5% (w/v) yeast extract as nitrogen source, and 0.9% (w/v) ι-carrageenan as carbon source. Then, the crude ι-carrageenase was characterized. The optimum temperature and pH of the ι-carrageenase were 40°C and 8.0, respectively. The enzymatic activity at 35­40°C for 45 min retained more than 40% of the maximum activity. Meanwhile, The ι-carrageenase was inhibited by the addition of 1 mmol/L Cd2+ and Fe3+ but increased by the addition of 1 mmol/L Ag+, Ba2+, Ca2+, Co2+, Mn2+, Zn2+, Fe2+, and Al3+. The structure of oligosaccharides derived from ι-carrageenan was detected using electrospray ionization mass spectrometry (ESI-MS). The ι-carrageenase degraded ι-carrageenan, yielding disaccharides and tetrasaccharides as main products. Conclusions: The discovery and study of new ι-carrageenases are beneficial not only for the production of ι-carrageenan oligosaccharides but also for the further utilization in industrial production.

Expression, purification and characterization of 3-Deoxy-D-manno-octulosonate 8-phosphate synthase from Phyllostachys edulis / 生物工程学报

3-Deoxy-D-manno-octulosonate 8-phosphate synthase (KDO8PS) is the key enzyme to synthesize eight-carbon sugar in plant and gram-negative bacterial cell wall. To analyze the polymerization and characterization in plant KDO8PS, the candidate gene was cloned from fresh Phyllostachys edulis seedling by RT-PCR. The open reading frame of PeKDO8PS is 876 bp deduced into 291 amino acid residues. The target protein was overexpressed in Escherichia coli induced by IPTG and then lager amount of fusion protein was purified through two-step methods with affinity chromatography and size-exclusion chromatography (SEC). SEC analysis shows that PeKDO8PS protein existed mainly in the form of dime in solution. Glutaraldehyde cross-linking experiments confirmed that the enzyme could form dimers. Further we identified that KDO8PS at high concentration two dimers could form tetramer in aqueous solution by analytical ultracentrifuge (AUC) analysis. The pH of the catalytic reaction was between 4.0 and 9.0, the optimum pH value was 8, the thermal stability range was between 25 and 65 ℃, and the optimum temperature was about 55 ℃. The enzyme activity was inhibited by some metal ions at lower concentrations, especially in the presence of Fe3+metal ion and activated by metal protease inhibitor EDTA at low concentration.

Expression, purification and characterization of arabinose-5-phosphate isomerase from Arabidopsis thaliana / 生物工程学报

Arabinose-5-phosphate isomerase (KdsD) is the first key limiting enzyme in the biosynthesis of 3-deoxy-D-manno-octulosonate (KDO). KdsD gene was cloned into prokaryotic expression vector pET-HTT by seamless DNA cloning method and the amount of soluble recombinant protein was expressed in a soluble form in E. coli BL21 (DE3) after induction of Isopropyl β-D-1-thiogalactopyranoside (IPTG). The target protein was separated and purified by Ni-NTA affinity chromatography and size exclusion chromatography, and its purity was more than 85%. Size exclusion chromatography showed that KdsD protein existed in three forms: polymers, dimmers, and monomers in water solution, different from microbial KdsD enzyme with the four polymers in water solution. Further, the purified protein was identified through Western blotting and MALDI-TOF MASS technology. The results of activity assay showed that the optimum pH and temperature of AtKdsD isomerase activities were 8.0 and 37 ℃, respectively. The enzyme was activated by metal protease inhibitor EDTA (5 mmol/L) and inhibited by some metal ions at lower concentration, especially with Co²⁺ and Cd²⁺ metal ion. Furthermore, when D-arabinose-5-phosphate (A5P) was used as substrate, Km and Vmax of AtKdsD values were 0.16 mmol/L, 0.18 mmol/L·min. The affinity of AtKdsD was higher than KdsD in E. coli combined with substrate. Above results have laid a foundation for the KdsD protein structure and function for its potential industrial application.

Screening and enzymatic study of a composite microbial system FH3

Five strains of fungi and 18 strains of bacteria were isolated from the soil and horse manure with cellulose as the sole carbon source. Among them, two fungal, F9 and F13, and two bacterial, B16 and B21, showed the highest filter paper activities, which were 7.79 U g-1, 9.84 U g-1, 7.34 U g-1 and 9.68 U g-1, respectively. Four microbial systems, designed as FH1 (F13+B21), FH2 (F13+B16+B21), FH3 (F9+B16+B21) and FH4 (F13+F9+B16+B21) were developed. The fermentation studies showed that the filter paper activity of the composite microbial system FH3 was higher than the others, which was 21.34 U g-1. The medium with bran and filter paper as the carbon source and peptone as nitrogen source was optimal and the maximum cellulase activity was reached at 30~35ºC and pH 6.0~6.5 when FH3 was incubated for 48 h. The enzymatic reaction conditions were estimated at 45~55 ºC, pH 4.5~5.5 and the thermal stability temperature was up to 60 ºC.

Research Progress on the Microbial L-Arabinose Isomerase / 微生物学通报

L-arabinose isomerase (L-AI) can isomerize L-arabinose and D-galactose into L-ribulose and D-tagatose, respectively, which is currently the most effective biological catalyst for D-tagatose production. The crystal structure of L-AI has been solved recently and its gene has been cloned, sequenced and overex- pressed. L-AI improved by protein engineering will be the dominant enzyme for industrial production of D-tagatose. This paper reviewed researches on protein structure and function, properties and application in D-tagatose production of L-AI, and the long-term potential development of L-AI was prospected.

Research on Alliinase Immobilization and Its Properties / 中国生物工程杂志

Alliinase is immobilized on pre-activated chitosan microspheres by glutaraldehyde.The optimum immobilization conditions are as follows: glutaraldehyde concentration is 4%,alliinase concentration 20.2U,immobilization time 2h.For immobilized alliinase,the highest activity was allowed at pH 7.0 and temperature 35℃,and the Michaelis constant(Km)was disclosed to be 7.9mmol/L by Lineweaver-Burk plot,and after 10 times reuses the immobilized alliinase lost no more than 10% activity.

Studies on the Production and Properties of Chitinase from Nomuraea rileyi Strain CQ031021 / 微生物学通报

The producing condition and properties of chitinase secreted by Nomuraea rileyi strain CQ031021 were studied.The optimal conditions for the strain to produce chitinase are 6 days of 28℃ with the initial pH 6.0,and the liquid medium containing 2.0% glucose as its carbon source and 0.6% peptone plus 0.6% beef extract as nitrogen source after inoculating dosage 2mL suspension of conidia(1?107/mL).The optimal temperature and pH for enzyme activity is 50℃ and 6.0,respectively,while the activity can be enhanced by Tween-80 and inhibited by SDS.The enzyme activity is stable under 40℃ and in pH range of 5.5～6.5.

Purification and Properties of L-Cysteine Synthetase from Pseudomonas / 微生物学通报

The L-ATC hydrolase and L-SCC amidohydrolase which convert L-ATC to L-cysteine in Pseudomonas sp.TS-1138 are purified about 83.9 and 90.3 fold by salting-out method, Sephadex G-75 gel chromatography, DEAE-cellulose 52 ion exchange and Sephadex G-100 gel chromatography, etc. The purified enzyemes are both demonstrated by SDS-PAGE to be a homogeneous protein. Their molecular weight are about 37.5kD and42.8kDa respectively. The optimum reaction temperature are both 35℃, and the optimum pH are 7.0 and 8.0 respectively. The Km of the two enzymes are 0.67 mmol/L and 0.15 mmol/L, and the Vmax are 0.39?10 -3mmol/L?min and 0.42?10 -3mmol/L?min respectively.