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Now showing items 49 - 56 of 56

  • Biodegradation characteristics and bioaugmentation potential of a novel quinoline-degrading strain of Bacillus sp. isolated from petroleum-contaminated soil

    Tuo, Bao-hua   Yan, Jia-bao   Fan, Bao-an   Yang, Zhong-hua   Liu, Jian-zhong  

    Quinoline and its derivatives are widely considered to be environmental pollutants. In this study, the biodegradation characteristics and bioaugmentation potential for a novel strain were described. The strain, named Q2, which could utilize quinoline as the sole carbon, nitrogen and energy source, was isolated and identified as a Bacillus sp. The optimum temperature, initial pH and shaker rotary speed for quinoline degradation were 30 degrees C, pH 8-10 and 100-200 rpm, respectively. During the biodegradation process, the quinoline-N was released as ammonium and the culture broth became yellow, pink and brown in turn, which indicated that several intermediates were generated. GC/MS analysis showed that 2(1H)-quinolinone and 8-hydroxycoumarin were produced. Furthermore, the bioaugmentation of Q2 into the sludge consortium, which was taken from refinery wastewater treatment plant, to degrade quinoline was investigated. The results showed that it could coexist with the other microbes and the remarkably enhanced quinoline biodegradation ability was achieved. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.
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  • Crp-Like Protein Plays Both Positive and Negative Roles in Regulating the Pathogenicity of Bacterial Pustule Pathogen Xanthomonas axonopodis pv. glycines

    Guo, Wei   Gao, Jie   Chen, Qingshan   Ma, Bojun   Fang, Yuan   Liu, Xia   Chen, Gongyou   Liu, Jian-Zhong  

    The global regulator Crp-like protein (Clp) is positively involved in the production of virulence factors in some of the Xanthomonas spp. However, the functional importance of Clp in X. axonopodis pv. glycines has not been investigated previously. Here, we showed that deletion of clp led to significant reduction in the virulence of X. axonopodis pv. glycines in soybean, which was highly correlated with the drastic reductions in carbohydrates utilization, extracellular polysaccharide (EPS) production, biofilm formation, cell motility, and synthesis of cell wall degrading enzymes (CWDEs). These significantly impaired properties in the clp mutant were completely rescued by a single-copy integration of the wildtype clp into the mutant chromosome via homologous recombination. Interestingly, overexpression of clp in the wild-type strain resulted in significant increases in cell motility and synthesis of the CWDEs. To our surprise, significant reductions in carbohydrates utilization, EPS production, biofilm formation, and the protease activity were observed in the wild-type strain overexpressing clp, suggesting that Clp also plays a negative role in these properties. Furthermore, quantitative reverse transcription polymerase chain reaction analysis suggested that clp was positively regulated by the diffusible signal factor-mediated quorumsensing system and the HrpG/ HrpX cascade. Taken together, our results reveal that Clp functions as both activator and repressor in multiple biological processes in X. axonopodis pv. glycines that are essential for its full virulence.
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  • The tobacco mosaic virus 126-kilodalton protein, a constituent of the virus replication complex, alone or within the complex aligns with and traffics along microfilaments

    Liu, Jian-Zhong   Blancaflor, Elison B.  

    Virus-induced cytoplasmic inclusion bodies ( referred to as virus replication complexes [VRCs]) consisting of virus and host components are observed in plant cells infected with tobacco mosaic virus, but the components that modulate their form and function are not fully understood. Here, we show that the tobacco mosaic virus 126-kD protein fused with green fluorescent protein formed cytoplasmic bodies (126-bodies) in the absence of other viral components. Using mutant 126-kD: green fluorescent fusion proteins and viral constructs expressing the corresponding mutant 126-kD proteins, it was determined that the size of the 126-bodies and the corresponding VRCs changed in synchrony for each 126-kD protein mutation tested. Through colabeling experiments, we observed the coalignment and intracellular trafficking of 126-bodies and, regardless of size, VRCs, along microfilaments (MFs). Disruption of MFs with MF-depolymerizing agents or through virus-induced gene silencing compromised the intracellular trafficking of the 126-bodies and VRCs and virus cell-to-cell movement, but did not decrease virus accumulation to levels that would affect virus movement or prevent VRC formation. Our results indicate that ( 1) the 126-kD protein modulates VRC size and traffics along MFs in cells; ( 2) VRCs traffic along MFs in cells, possibly through an interaction with the 126-kD protein, and the negative effect of MF antagonists on 126-body and VRC intracellular movement and virus cell-to-cell movement correlates with the disruption of this association; and ( 3) virus movement was not correlated with VRC size.
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  • Glycerol Dehydratases:Biochemical Structures,Catalytic Mechanisms,and Industrial Applications in 1,3-Propanediol Production by Naturally Occurring and Genetically Engineered Bacterial Strains

    Liu, Jian-zhong   Xu, Wu   Chistoserdov, Andrei   Bajpai, Rakesh K.  

    To date, two types of glycerol dehydratases have been reported: coenzyme B-12-dependent and coenzyme B-12-independent glycerol dehydratases. The three-dimensional structure of the former is a dimer of alpha beta gamma heterotrimer, while that of the latter is a homodimer. Their mechanisms of reaction are typically enzymatic radical catalysis. Functional radical in both the glycerol dehydratases is the adenosyl radical. However, the adenosyl radical in the former originates from coenzyme B-12 by homolytic cleavage, and that in the latter from S-adenosyl-methionine. Until some years ago, Clostridium butyricum VPI 1718 was the only microorganism known to possess B-12-independent glycerol dehydratase, but since then, several other bacteria with this unique capability have been identified. This article focuses on the glycerol dehydratases and on 1,3-propanediol production from glycerol by naturally occurring and genetically engineered bacterial strains containing glycerol dehydratase.
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  • Glycerol Dehydratases: Biochemical Structures, Catalytic Mechanisms, and Industrial Applications in 1,3-Propanediol Production by Naturally Occurring and Genetically Engineered Bacterial Strains

    Liu, Jian-zhong   Xu, Wu   Chistoserdov, Andrei   Bajpai, Rakesh K.  

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  • Combining directed evolution of pathway enzymes and dynamic pathway regulation using a quorum-sensing circuit to improve the production of 4-hydroxyphenylacetic acid in Escherichia coli

    Shen, Yu-Ping   Fong, Lai San   Yan, Zhi-Bo   Liu, Jian-Zhong  

    Background4-Hydroxyphenylacetic acid (4HPAA) is an important building block for synthesizing drugs, agrochemicals, biochemicals, etc. 4HPAA is currently produced exclusively via petrochemical processes and the process is environmentally unfriendly and unsustainable. Microbial cell factory would be an attractive approach for 4HPAA production.ResultsIn the present study, we established a microbial biosynthetic system for the de novo production of 4HPAA from glucose in Escherichia coli. First, we compared different biosynthetic pathways for the production of 4HPAA. The yeast Ehrlich pathway produced the highest level of 4HPAA among these pathways that were evaluated. To increase the pathway efficiency, the yeast Ehrlich pathway enzymes were directedly evolved via error-prone PCR. Two phenylpyruvate decarboxylase ARO10 and phenylacetaldehyde dehydrogenase FeaB variants that outperformed the wild-type enzymes were obtained. These mutations increased the in vitro and in vivo catalytic efficiency for converting 4-hydroxyphenylpyruvate to 4HPAA. A tunable intergenic region (TIGR) sequence was inserted into the two evolved genes to balance their expression. Regulation of TIGR for the evolved pathway enzymes further improved the production of 4HPAA, resulting in a 1.13-fold increase in titer compared with the fusion wild-type pathway. To prevent the toxicity of a heterologous pathway to the cell, an Esa quorum-sensing (QS) circuit with both activating and repressing functions was developed for inducer-free productions of metabolites. The Esa-P-esaR activation QS system was used to dynamically control the biosynthetic pathway of 4HPAA in E. coli, which achieved 17.390.26g/L with a molar yield of 23.2% without addition of external inducers, resulting in a 46.4% improvement of the titer compared to the statically controlled pathway.Conclusion p id=3DPar3 We have constructed an E. coli for 4HPAA production with the highest titer to date. This study also demonstrates that the combination of directed evolution of pathway enzymes and dynamic pathway regulation using a QS circuit is a powerful strategy of metabolic engineering for the productions of metabolites.
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  • [IEEE 2009 5th International Conference on Wireless Communications, Networking and Mobile Computing (WiCOM) - Beijing, China (2009.09.24-2009.09.26)] 2009 5th International Conference on Wireless Communications, Networking and Mobile Computing - Windowed All-Phase DFT Modulated in Time Domain and Its Application in Spectrum Analysis

    Liu, Jian-Zhong   Hou, Zheng-Xin   Wang, Cheng-You  

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  • Purification, kinetic and thermodynamic studies of a new ribonuclease from a mutant of Aspergillus niger

    Xiong, Ya-Hong   Liu, Jian-Zhong   Song, Hai-Yan  

    Ribonuclease was purified from Aspergillus niger SA-13-20 to homogeneity level by using (NH4)(2)SO4 precipitation. DEAE-cellulose anion-exchange chromatography, ultrafiltration and Sephacryl HR-200 chromatography, The molecular weight and isoelectric point of the enzyme was 40.1 kDa and 5.3, respectively, The pH- and temperature-dependent kinetic parameters were determined. The RNase showed the strongest affinity with RNA as the substrate, and the highest catalytic efficiency for hydrolysis of the substrate at pH 3.5 and 65 degrees C. It exhibited Michaelis-Menten Kinetics with k(cat) of 118.1 s(-1) and K-m of 57.0 mu g ml(-1). respectively. Thermodynamic parameters for catalysis and thermal denaturation were also determined, Activation energy (E-a) for catalysis of A. niger SA-13-20 RNase was 50.31 kJ mol(-1) and free energy (Delta G(#)), enthalpy (Delta H-#) and entropy (Delta S-#) of activation for catalysis of the enzyme at 65 degrees C were 69.76, 47.50 and -65.83 J mol(-1) K (1), respectively, Activation energy (E-a,E-d) for denaturation of the enzyme was 200.53 kJ mol(-1) and free energy (Delta G(d)(#)), enthalpy (Delta H-d(#)) and entropy (Delta S-d(#)) of activation for denaturation of the enzyme at 45 degrees C were 79.18 kJ mol(1), 197.88 and 373.09 J mol (1) K (1), respectively, (C) 2005 Elsevier B.V. All rights reserved.
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