• Journal of Microbiology and Biotechnology
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• 제24권12호
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• pp.1685-1689
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• 2014

Baeyer-Villiger (BV) oxidation of cyclohexanone to ${\varepsilon}$-caprolactone in a microbial system expressing cyclohexanone monooxygenase (CHMO) can be influenced by not only the efficient regeneration of NADPH but also a sufficient supply of oxygen. In this study, the bacterial hemoglobin gene from Vitreoscilla stercoraria (vhb) was introduced into the recombinant Escherichia coli expressing CHMO to investigate the effects of an oxygen-carrying protein on microbial BV oxidation of cyclohexanone. Coexpression of Vhb allowed the recombinant E. coli strain to produce a maximum ${\varepsilon}$-caprolactone concentration of 15.7 g/l in a fed-batch BV oxidation of cyclohexanone, which corresponded to a 43% improvement compared with the control strain expressing CHMO only under the same conditions.

• Journal of Microbiology and Biotechnology
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• 제27권1호
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• pp.92-100
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• 2017

Acetoin (AC) is a volatile platform compound with various potential industrial applications. AC contains two stereoisomeric forms: (3S)-AC and (3R)-AC. Optically pure AC is an important potential intermediate and widely used as a precursor to synthesize novel optically active materials. In this study, chiral (3R)-AC production from meso-2,3-butanediol (meso-2,3-BD) was obtained using recombinant Escherichia coli cells co-expressing meso-2,3-butanediol dehydrogenase (meso-2,3-BDH), NADH oxidase (NOX), and hemoglobin protein (VHB) from Serratia sp. T241, Lactobacillus brevis, and Vitreoscilla, respectively. The new biocatalyst of E. coli/pET-mbdh-nox-vgb was developed and the bioconversion conditions were optimized. Under the optimal conditions, 86.74 g/l of (3R)-AC with the productivity of 3.61 g/l/h and the stereoisomeric purity of 97.89% was achieved from 93.73 g/l meso-2,3-BD using the whole-cell biocatalyst. The yield and productivity were new records for (3R)-AC production. The results exhibit the industrial potential for (3R)-AC production via whole-cell biocatalysis.

• Journal of Microbiology and Biotechnology
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• 제25권9호
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• pp.1433-1441
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• 2015

Pollution resulting from the discharge of textile dyes into water systems has become a major global concern. Because peroxidases are known for their ability to decolorize and detoxify textile dyes, the peroxidase activity of Vitreoscilla hemoglobin (VHb) has recently been studied. It is found that VHb and variants of this enzyme show great promise for enzymatic decolorization of dyes and may play a role in achieving their successful removal from industrial wastewater. The level of VHb peroxidase activity correlates with two amino acid residues present within the conserved distal pocket, at positions 53 and 54. In this work, sitedirected mutagenesis of these residues was performed and resulted in improved VHb peroxidase activity. The double mutant, Q53H/P54C, shows the highest dye decolorization and removal efficiency, with 70% removal efficiency within 5 min. UV spectral studies of Q53H/P54C reveals a more compact structure and an altered porphyrin environment (λ_Soret = 413 nm) relative to that of wild-type VHb (λ_Soret = 406), and differential scanning calorimetry data indicate that the VHb variant protein structure is more stable. In addition, circular dichroism spectroscopic studies indicate that this variant's increased protein structural stability is due to an increase in helical structure, as deduced from the melting temperature, which is higher than 90℃. Therefore, the VHb variant Q53H/P54C shows promise as an excellent peroxidase, with excellent dye decolorization activity and a more stable structure than wild-type VHb under high-temperature conditions.

• Molecular & Cellular Toxicology
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• 제1권4호
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• pp.262-267
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• 2005

Using genetic engineering, the Vitreoscilla (bacterial) hemoglobin gene (vgb) was integrated stably into the chromosomes of and Burkholderia cepacia. Similar to previous results, the wild type VHb improved growth for Burkholderia cepacia and degradation of benzoic acid under both normal and low aeration conditions. The stable expression of VHb enhanced these parameters. The results demonstrate the possibility that the positive effects provided by VHb may be augmented by protein engineering.

• Journal of Microbiology and Biotechnology
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• 제17권12호
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• pp.2066-2070
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• 2007

It was found that Shinorhizobium meliloti hemoprotein (SM) was more effective than Vitreoscilla hemoglobin (Vhb) in promoting secondary metabolites production when overexpressed in Streptomyces lividans TK24. The transformant with sm (sm-transformant) produced 2.7-times and 3-times larger amounts of actinorhodin than the vhb-transformant in solid culture and flask culture, respectively. In both solid and flask cultures, a larger amount of undecylprodigiocin was produced by the sm-transformant. It is considered that the overexpression of SM especially has activated the pentose phosphate pathway through oxidative stress, as evidenced by an increased NADPH production observed, and that it has promoted secondary metabolites biosynthesis.

• Journal of Microbiology and Biotechnology
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• 제19권9호
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• pp.869-872
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• 2009

The cyclic undecapeptide cyclosporin A (CyA), one of the most valuable immunosuppressive drugs, is produced nonribosomally by a multifunctional cyclosporin synthetase enzyme complex by the filamentous fungus Tolypocladium niveum. To increase CyA productivity by wild-type T. niveum (ATCC 34921), random mutagenesis was first performed using an antifungal agar-plug colony assay (APCA) selection approach. This generated a mutant strain producing more than 9-fold greater CyA than the wild-type strain. Additionally, a foreign bacterial gene, Vitreoscilla hemoglobin gene (VHb), was transformed via protoplast regeneration and its transcription was confirmed by RT-PCR in the UV-irradiated mutant cell. This led to an additional 33.5% increase of CyA production. Although most protoplast-regenerated T. niveum transformants tend to lose CyA productivity, the optimized combination of random mutagenesis and protoplast transformation described here should be an efficient strategy to generate a commercially valuable, yet metabolite low-producing, fungal species, such as CyA-producing T. niveum.