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1.
Cao-Hoang L Dumont F Marechal PA Le-Thanh M Gervais P 《Applied microbiology and biotechnology》2008,77(6):1379-1387
The effects of slow chilling (2°C min−1) and rapid chilling (2,000°C min−1) were investigated on the survival and membrane fluidity of Escherichia coli, of Bacillus subtilis, and of Saccharomyces cerevisiae. Cell death was found to be dependent on the physiological state of cell cultures and on the rate of temperature downshift.
Slow temperature decrease allowed cell stabilization, whereas the rapid chilling induced an immediate loss of viability of
up to more than 90 and 70% for the exponentially growing cells of E. coli and B. subtilis, respectively. To relate the results of viability with changes in membrane physical state, membrane anisotropy variation
was monitored during thermal stress using the fluorescence probe 1,6-diphenyl-1,3,5-hexatriene. No variation in the membrane
fluidity of all the three microorganisms was found after the slow chilling. It is interesting to note that fluorescence measurements
showed an irreversible rigidification of the membrane of exponentially growing cells of E. coli and B. subtilis after the instantaneous cold shock, which was not observed with S. cerevisiae. This irreversible effect of the rapid cold shock on the membrane correlated well with high rates of cell inactivation. Thus,
membrane alteration seems to be the principal cause of the cold shock injury. 相似文献
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Anping Su Qijun Yu Ying Luo Jinshui Yang Entao Wang Hongli Yuan 《Microbial biotechnology》2021,14(6):2279-2290
Gamma-aminobutyric acid (GABA) and delta-aminolevulinic acid (ALA), playing important roles in agriculture, medicine and other fields, are multifunctional non-protein amino acids with similar and comparable properties and biosynthesis pathways. Recently, microbial synthesis has become an inevitable trend to produce GABA and ALA due to its green and sustainable characteristics. In addition, the development of metabolic engineering and synthetic biology has continuously accelerated and increased the GABA and ALA yield in microorganisms. Here, focusing on the current trends in metabolic engineering strategies for microbial synthesis of GABA and ALA, we analysed and compared the efficiency of various metabolic strategies in detail. Moreover, we provide the insights to meet challenges of realizing industrially competitive strains and highlight the future perspectives of GABA and ALA production. 相似文献
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Daniel E. Agnew Amanda K. Stevermer J.Tyler Youngquist Brian F. Pfleger 《Metabolic engineering》2012,14(6):705-713
Demand for sustainable materials motivates the development of microorganisms capable of synthesizing products from renewable substrates. A challenge to commercial production of polyhydroxyalkanoates (PHA), microbially derived polyesters, is engineering metabolic pathways to produce a polymer with the desired monomer composition from an unrelated and renewable source. Here, we demonstrate a metabolic pathway for converting glucose into medium-chain-length (mcl)-PHA composed primarily of 3-hydroxydodecanoate monomers. This pathway combines fatty acid biosynthesis, an acyl-ACP thioesterase to generate desired C12 and C14 fatty acids, β-oxidation for conversion of fatty acids to (R)-3-hydroxyacyl-CoAs, and a PHA polymerase. A key finding is that Escherichia coli expresses multiple copies of enzymes involved in β-oxidation under aerobic conditions. To produce polyhydroxydodecanoate, an acyl-ACP thioesterase (BTE), an enoyl-CoA hydratase (phaJ3), and mcl-PHA polymerase (phaC2) were overexpressed in E. coli ΔfadRABIJ. Yields were improved through expression of an acyl-CoA synthetase resulting in production over 15% CDW – the highest reported production of mcl-PHA of a defined composition from an unrelated carbon source. 相似文献
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Peter K. Matzinger Hans G. W. Leuenberger 《Applied microbiology and biotechnology》1985,22(3):208-210
Summary 107 Microorganisms selected from 26 genera belonging to bacteria, actinomycetes, fungi and yeasts were screened for their ability to reduce -formyl-esters stereoselectively. Eighteen strains have been found which were able to reduce at least one of 5 substrates tested with an optical purity of more than 85% ee. The best strains were Candida humicola, Aspergillus petrakii, Streptomyces hydrogenans and Streptomyces griseus. The dependence of the enantioselectivity of the reduction on the group of microorganisms and on the substituents of the formyl-esters is discussed. 相似文献
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Aoshima M 《Applied microbiology and biotechnology》2007,76(2):249-255
The tricarboxylic acid (TCA) cycle is an energy-producing pathway for aerobic organisms. However, it is widely accepted that
the phylogenetic origin of the TCA cycle is the reductive TCA cycle, which is a non-Calvin-type carbon-dioxide-fixing pathway.
Most of the enzymes responsible for the oxidative and reductive TCA cycles are common to the two pathways, the difference
being the direction in which the reactions operate. Because the reductive TCA cycle operates in an energetically unfavorable
direction, some specific mechanisms are required for the reductive TCA-cycle-utilizing organisms. Recently, the molecular
mechanism for the “citrate cleavage reaction” and the “reductive carboxylating reaction from 2-oxoglutarate to isocitrate”
in Hydrogenobacter thermophilus have been demonstrated. Both of these reactions comprise two distinct consecutive reactions, each catalyzed by two novel
enzymes. Sequence analyses of the newly discovered enzymes revealed phylogenetic and functional relationships between other
TCA-cycle-related enzymes. The occurrence of novel enzymes involved in the citrate-cleaving reaction seems to be limited to
the family Aquificaceae. In contrast, the key enzyme in the reductive carboxylation of 2-oxoglutarate appears to be more widely distributed in extant
organisms. The four newly discovered enzymes have a number of potential biotechnological applications. 相似文献
8.
Halotolerant microalga Dunaliella, which is exploited for the production of dried biomass or cell extract, is used as a medicinal food. With the advancement
in this field in recent years, the production of bio-organic compounds such as β-carotene is established in many countries.
Large-scale production of β-carotene is controlled by numerous stress factors like high light intensity, high salinity, temperature
and availability of nutrients. The state-of-the-art strategies in industries in closed systems under new set of inductive
factors will additionally promote the ease of commercial production of β-carotene. This review mainly focuses on the different
methodologies employed recently for the optimum production of β-carotene from Dunaliella species. 相似文献
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G-Rich oligonucleotides with cytosine residues in their sequences can form G-quadruplexes where G-quartets are flanked by G·C Watson-Crick base pairs. In an attempt to probe the role of cations in stabilization of a structural element with two G·C base pairs stacked on a G-quartet, we utilized solution state nuclear magnetic resonance to study the folding of the d(G(3)CT(4)G(3)C) oligonucleotide into a G-quadruplex upon addition of (15)NH(4)(+) ions. Its bimolecular structure exhibits antiparallel strands with edge-type loops. Two G-quartets in the core of the structure are flanked by a couple of Watson-Crick G·C base pairs in a sheared arrangement. The topology is equivalent to the solution state structure of the same oligonucleotide in the presence of Na(+) and K(+) ions [Kettani, A., et al. (1998) J. Mol. Biol.282, 619, and Bouaziz, S., et al. (1998) J. Mol. Biol.282, 637). A single ammonium ion binding site was identified between adjacent G-quartets, but three sites were expected. The remaining potential cation binding sites between G-quartets and G·C base pairs are occupied by water molecules. This is the first observation of long-lived water molecules within a G-quadruplex structure. The flanking G·C base pairs adopt a coplanar arrangement and apparently do not require cations to neutralize unfavorable electrostatic interactions among proximal carbonyl groups. A relatively fast movement of ammonium ions from the inner binding site to bulk with the rate constants of 21 s(-1) was attributed to the lack of hydrogen bonds between adjacent G·C base pairs and the flexibility of the T(4) loops. 相似文献
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Pavlova K. Angelova G. Savova I. Grigorova D. Kupenov L. 《World journal of microbiology & biotechnology》2002,18(6):569-573
Moss and lichen samples from the region of the Bulgarian base on Livingston Island, Antarctica were examined for the presence of yeasts. Six pure cultures were obtained. They were screened for -glucosidase production and two of them were selected. These were identified as Cryptococcus albidus AL2 and C. albidus AL3, according to their morphology, reproductive behaviour, and growth at different temperatures, salt concentrations, nutritional characteristics and various biochemical tests. These strains were examined for biosynthesis of -glucosidase on different carbon sources under aerobic conditions. High exocellular and endocellular activities were obtained when they were grown on cellobiose, methyl--D-glucopyranoside and salicin. The time course of growth and -glucosidase production of the yeast was examined by cultivation in a medium with cellobiose under aerobic conditions at temperatures 18 and 24 °C for 96 h. Cryptococcus albidus AL2 and C. albidus AL3 synthesized exocellular enzyme, respectively 58.33 and 55.83 U/ml and endocellular enzyme 137.75 and 205.34 U/ml at 24 °C for 72 h of the cultivation. 相似文献
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Traditional cultivation-based methods to quantify microbial abundance are not suitable for analyses of microbial communities
in environmental or medical samples, which consist mainly of uncultured microorganisms. Recently, different cultivation-independent
quantification approaches have been developed to overcome this problem. Some of these techniques use specific fluorescence
markers, for example ribosomal ribonucleic acid targeted oligonucleotide probes, to label the respective target organisms.
Subsequently, the detected cells are visualized by fluorescence microscopy and are quantified by direct visual cell counting
or by digital image analysis. This article provides an overview of these methods and some of their applications with emphasis
on (semi-)automated image analysis solutions. 相似文献
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Youl Her Young-Chul Lee Jin-Hwan Oh Yoon-E Choi Chang-Woo Lee Jin-Suk Kim Hwan Mook Kim Ji-Won Yang 《Biotechnology and Bioprocess Engineering》2012,17(3):538-546
Over the past several decades, the pharmacological effects of ginsenosides in Panax ginseng roots have been extensively investigated. Here, we developed a method for producing specific ginsenosides (F1 and F2) with good yields (F1:162 mg/g, F2:305 mg/g) using ??-glycosidase purified from Aspergillus niger. In addition, each ginsenoside (at least 25 species) was separated and purified by high performance liquid chromatography (HPLC) using five different types of solvents and different purification steps. In addition, the Rg3:Rh2 mixture (1:1, w/w) was shown to inhibit a specific lung cancer cell line (NCI-H232) in vivo, displaying an anticancer effect at a dose lower than achieved using treatments with single Rg3 or Rh2. This finding suggests that the combination of ginsenosides for targeting anticancer is more effective than the use of a single ginsenoside from ginseng or red ginseng. 相似文献
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Boyapati Gokul Je-Hyuk Lee Ki-Bang Song T. Panda Sang-Ki Rhee Chul-Ho Kim 《Biotechnology and Bioprocess Engineering》2000,5(1):57-60
(R)-β-acetylmercaptoisobutyric acid (RAM), a chiral compound, is an important intermediate for the chemical synthesis of various
antihypertensive and congestive heart failure drugs. Microorganisms capable of converting (R,S)-β-acetylmercaptoisobutyric
acid ((R,S)-ester) to RAM were screened from soil microorganisms. A strain ofPseudomonas sp. 1001 screened from a soil sample was selected to be the best. Cells showed an activity of 540 U/mL from culture broth
and the enzyme was thermostable up to 70°C. This strain could produce RAM asymmetrically from (R,S)-ester. 相似文献
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Phimchanok Nakkharat Dietmar Haltrich 《World journal of microbiology & biotechnology》2007,23(6):759-764
The β-galactosidase from Talaromyces thermophilus CBS 236.58 immobilized onto Eupergit C produced galacto-oligosaccharides (GalOS) in batchwise and continuous packed-bed mode
of operation. A maximum yield of GalOS of 12, 39 and 80 g l−1 was obtained for initial lactose concentrations of 50, 100 and 200 g l−1, respectively, for batch conversion experiments. The immobilized enzyme could be re-used for several cycles for lactose hydrolysis
and transformation. The maximum GalOS concentration of approximately 50 g l−1 was obtained with the dilution rate of 0.375 h−1 in a packed-bed reactor, when using an initial lactose concentration of 200 g l−1. Continuous conversion of lactose in the packed-bed reactor resulted in the formation of relatively more trisaccharides than
when employing the immobilized enzyme in discontinuous mode of operation. 相似文献
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Sesquiterpenes are important materials in pharmaceuticals and industry. Metabolic engineering has been successfully used to produce these valuable compounds in microbial hosts. However, the microbial potential of sesquiterpene production is limited by the poor heterologous expression of plant sesquiterpene synthases and the deficient FPP precursor supply. In this study, we engineered E. coli to produce α-farnesene using a codon-optimized α-farnesene synthase and an exogenous MVA pathway. Codon optimization of α-farnesene synthase improved both the synthase expression and α-farnesene production. Augmentation of the metabolic flux for FPP synthesis conferred a 1.6- to 48.0-fold increase in α-farnesene production. An additional increase in α-farnesene production was achieved by the protein fusion of FPP synthase and α-farnesene synthase. The engineered E. coli strain was able to produce 380.0 mg/L of α-farnesene, which is an approximately 317-fold increase over the initial production of 1.2 mg/L. 相似文献