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941.
Development of sucrose-utilizing Escherichia coli K-12 strain by cloning β-fructofuranosidases and its application for l-threonine production 总被引:1,自引:0,他引:1
Jeong Wook Lee Sol Choi Jin Hwan Park Claudia E. Vickers Lars K. Nielsen Sang Yup Lee 《Applied microbiology and biotechnology》2010,88(4):905-913
Sucrose is one of the most promising carbon sources for industrial fermentation. To achieve sucrose catabolism, the sucrose
utilization operons have been introduced into microorganisms that are not able to utilize sucrose. However, the rates of growth
and sucrose uptake of these engineered strains were relatively low to be successfully employed for industrial applications.
Here, we report a practical example of developing sucrose-utilizing microorganisms using Escherichia coli K-12 as a model system. The sucrose utilizing ability was acquired by introducing only β-fructofuranosidase from three different
sucrose-utilizing organisms (Mannheimia succiniciproducens, E. coli W, and Bacillus subtilis). Among them, the M. succiniciproducens β-fructofuranosidase was found to be the most effective for sucrose utilization. Analyses of the underlying mechanism revealed
that sucrose was hydrolyzed into glucose and fructose in the extracellular space and both liberated hexoses could be transported
by their respective uptake systems in E. coli K-12. To prove that this system can also be applied for the production of useful metabolites, the M. succiniciproducens β-fructofuranosidase was introduced into the engineered l-threonine production strain of E. coli K-12. This recombinant strain was able to produce 51.1 g/L l-threonine by fed-batch culture, resulting in an overall yield of 0.284 g l-threonine per g sucrose. This simple approach to make E. coli K-12 to acquire sucrose-utilizing ability and its successful biotechnological application can be employed to develop sustainable
bioprocesses using renewable biomass. 相似文献
942.
A. C. Krüger M. K. Raarup M. M. Nielsen M. Kristensen F. Besenbacher J. Kjems V. Birkedal 《European biophysics journal : EBJ》2010,39(9):1343-1350
G-rich telomeric DNA sequences can form G-quadruplex structures. The heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1)
and a shortened derivative (UP1) are active in telomere length regulation, and it has been reported that UP1 can unwind G-quadruplex
structures. Here, we investigate the interaction of hnRNP A1 with G-quadruplex DNA structures containing the human telomere
repeat (TTAGGG) by gel retardation assays, ensemble fluorescence energy transfer (FRET) spectroscopy, and single molecule
FRET microscopy. Our biochemical experiments show that hnRNP A1 binds well to the G-quadruplex telomeric DNA. Ensemble and
single molecule FRET measurements provide further insight into molecular conformation: the telomeric DNA overhang is found
to be in a folded state in the absence of hnRNP A1 and to remain predominantly in a compact state when complexed with hnRNP
A1. This finding is in contrast to the previously reported crystal structures of UP1-telomere DNA complexes where the DNA
oligo within the protein-DNA complex is in a fully open conformation. 相似文献
943.
Hector F. Rivera‐Gutierrez Erik Matthysen Frank Adriaensen Hans Slabbekoorn 《Ethology : formerly Zeitschrift fur Tierpsychologie》2010,116(10):951-960
Birdsong can play a critical role in establishing a territory and finding a mate among individuals from local and foreign populations. Variation in birdsong among populations can be influenced by habitat fragmentation and might affect successful dispersal among habitat fragments. We studied variation in great tit song in a long‐term study population distributed over nine forest fragments. All individual males recorded had a known dispersal history within the fragmented forest habitat. We found spatial structure of declining song‐type sharing with distance, with a marked drop from an individual’s own forest fragment to another across a habitat gap. We also found decreasing song similarity among increasingly distant fragments in terms of temporal and spectral characteristics of shared song types. The change in acoustic structure was more gradual and seemed less affected by habitat discontinuity but also showed a tight correlation with dispersal index among forest fragments. Immigrant birds shared fewer song types with neighbouring birds that were born within the same forest fragment, but not less compared to birds born in another forest fragment within the study area. Our data provide detailed insight into the relationship between song differentiation and male dispersal and contribute to our understanding of the potential role of song in reproductive exchange and avian speciation. The fact that birds in small forest fragments shared more songs than birds in larger forest fragments confirms that song analysis has potential as a tool for conservation in rare species. 相似文献
944.
Ke-Ke Cheng Jian-An Zhang Erik Chavez Jin-Ping Li 《Applied microbiology and biotechnology》2010,87(2):411-417
Xylitol production from corncob hemicellulose is a popular process in China. Microbial conversion of xylose to xylitol, as
a biological process with many advantages, has drawn increasing attention. As a by-product from the manufacturing of xylitol,
corncob cellulosic residues are produced in very large amounts and represent an environmental problem. As a result, considering
the large amount of xylitol production in China, the conversion of corncob cellulosic residues has become a widespread issue
having to be tackled. After the hemicellulose in corncob has been hydrolyzed for xylitol production, the corncob cellulosic
residue is porous and can easily be hydrolyzed by cellulases into glucose and further converted to ethanol, another high-added-value
chemical. Based on the latest technology advancements in xylitol, cellulase, and ethanol production, the integrated production
of ethanol from corncob cellulosic residues appears as a promising way to improve the profit of the whole xylitol production
process. 相似文献
945.
Thomsen R Sølvsten CA Linnet TE Blechingberg J Nielsen AL 《Journal of bioinformatics and computational biology》2010,8(5):885-900
A common method for calculating results from qPCR experiments is the comparative Ct method, also called the 2(-ΔΔCt) method. However, several assumptions are included in the 2(-ΔΔCt) method and standard statistical analyses are not directly applicable. Here, we describe a different method, the X(0) method, for result calculations and statistical analysis from qPCR experiments. The X(0) method differs from the 2(-ΔΔCt) method by introducing a conversion of the exponentially related Ct values into linearly related X(0) values, which represent the amount of starting material in a qPCR experiment. Results calculated by the X(0) method are illustrated for qPCR experiments with technical and biological replicates, including procedures to calculate standard deviations. Incorporation of primer efficiencies in calculations by the X(0) method is also described. Altogether, the X(0) method constitutes a very simple and accurate alternative to the 2(-ΔΔCt) method for result calculations from qPCR data. 相似文献
946.
947.
Böhlenius H Mørch SM Godfrey D Nielsen ME Thordal-Christensen H 《The Plant cell》2010,22(11):3831-3844
Host cell vesicle traffic is essential for the interplay between plants and microbes. ADP-ribosylation factor (ARF) GTPases are required for vesicle budding, and we studied the role of these enzymes to identify important vesicle transport pathways in the plant-powdery mildew interaction. A combination of transient-induced gene silencing and transient expression of inactive forms of ARF GTPases provided evidence that barley (Hordeum vulgare) ARFA1b/1c function is important for preinvasive penetration resistance against powdery mildew, manifested by formation of a cell wall apposition, named a papilla. Mutant studies indicated that the plasma membrane-localized REQUIRED FOR MLO-SPECIFIED RESISTANCE2 (ROR2) syntaxin, also important for penetration resistance, and ARFA1b/1c function in the same vesicle transport pathway. This was substantiated by a requirement of ARFA1b/1c for ROR2 accumulation in the papilla. ARFA1b/1c is localized to multivesicular bodies, providing a functional link between ROR2 and these organelles in penetration resistance. During Blumeria graminis f sp hordei penetration attempts, ARFA1b/1c-positive multivesicular bodies assemble near the penetration site hours prior to the earliest detection of callose in papillae. Moreover, we showed that ARFA1b/1c is required for callose deposition in papillae and that the papilla structure is established independently of ARFA1b/1c. This raises the possibility that callose is loaded into papillae via multivesicular bodies, rather than being synthesized directly into this cell wall apposition. 相似文献
948.
Erik Vollbrecht Jon Duvick Justin P. Schares Kevin R. Ahern Prasit Deewatthanawong Ling Xu Liza J. Conrad Kazuhiro Kikuchi Tammy A. Kubinec Bradford D. Hall Rebecca Weeks Erica Unger-Wallace Michael Muszynski Volker P. Brendel Thomas P. Brutnell 《The Plant cell》2010,22(6):1667-1685
The maize (Zea mays) transposable element Dissociation (Ds) was mobilized for large-scale genome mutagenesis and to study its endogenous biology. Starting from a single donor locus on chromosome 10, over 1500 elements were distributed throughout the genome and positioned on the maize physical map. Genetic strategies to enrich for both local and unlinked insertions were used to distribute Ds insertions. Global, regional, and local insertion site trends were examined. We show that Ds transposed to both linked and unlinked sites and displayed a nonuniform distribution on the genetic map around the donor r1-sc:m3 locus. Comparison of Ds and Mutator insertions reveals distinct target preferences, which provide functional complementarity of the two elements for gene tagging in maize. In particular, Ds displays a stronger preference for insertions within exons and introns, whereas Mutator insertions are more enriched in promoters and 5′-untranslated regions. Ds has no strong target site consensus sequence, but we identified properties of the DNA molecule inherent to its local structure that may influence Ds target site selection. We discuss the utility of Ds for forward and reverse genetics in maize and provide evidence that genes within a 2- to 3-centimorgan region flanking Ds insertions will serve as optimal targets for regional mutagenesis. 相似文献
949.
950.
Peter Beemiller Youxin Zhang Suresh Mohan Erik Levinsohn Isabella Gaeta Adam D. Hoppe Joel A. Swanson 《Molecular biology of the cell》2010,21(3):470-480
Fcγ Receptor (FcR)-mediated phagocytosis by macrophages requires phosphatidylinositol 3-kinase (PI3K) and activation of the Rho-family GTPases Cdc42 and Rac1. Cdc42 is activated at the advancing edge of the phagocytic cup, where actin is concentrated, and is deactivated at the base of the cup. The timing of 3′ phosphoinositide (3′PI) concentration changes in cup membranes suggests a role for 3′PIs in deactivation of Cdc42. This study examined the relationships between PI3K and the patterns of Rho-family GTPase signaling during phagosome formation. Inhibition of PI3K resulted in persistently active Cdc42 and Rac1, but not Rac2, in stalled phagocytic cups. Patterns of 3′PIs and Rho-family GTPase activities during phagocytosis of 5- and 2-μm-diameter microspheres indicated similar underlying mechanisms despite particle size–dependent sensitivities to PI3K inhibition. Expression of constitutively active Cdc42(G12V) increased 3′PI concentrations in plasma membranes and small phagosomes, indicating a role for Cdc42 in PI3K activation. Cdc42(G12V) inhibited phagocytosis at a later stage than inhibition by dominant negative Cdc42(N17). Together, these studies identified a Cdc42 activation cycle organized by PI3K, in which FcR-activated Cdc42 stimulates PI3K and actin polymerization, and the subsequent increase of 3′PIs in cup membranes inactivates Cdc42 to allow actin recycling necessary for phagosome formation. 相似文献