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This paper evaluates the critical flux obtained by different techniques including tests with different flux step lengths (20 and 40 min and 7 days) and modes of operation (continuous and intermittent) under low and high MLSS concentrations. The paper also analyses a couple of long-term tests (flow rate of 40 and 20 L/day) to obtain the time required to reach the critical flux experimentally and compares those values with the results obtained numerically from a mathematical model. It was found that intermittent mode with membrane relaxation was useful in controlling the fouling of membrane and in restoring the membrane from fouling at lower MLSS. 相似文献
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Two-Component Anti-Staphylococcus aureus Lantibiotic Activity Produced by Staphylococcus aureus C55 下载免费PDF全文
Staphylococcus aureus C55 was shown to produce bacteriocin activity comprising three distinct peptide components, termed staphylococcins C55α, C55β, and C55γ. The three peptides were purified to homogeneity by a simple four-step purification procedure that consisted of ammonium sulfate precipitation followed by XAD-2 and reversed-phase (C8 and C18) chromatography. The yield following C8 chromatography was about 86%, with a more-than-300-fold increase in specific activity. When combined in approximately equimolar amounts, staphylococcins C55α and C55β acted synergistically to kill S. aureus or Micrococcus luteus but not S. epidermidis strains. The N-terminal amino acid sequences of all three peptides were obtained and staphylococcins C55α and C55β were shown to be lanthionine-containing (lantibiotic) molecules with molecular weights of 3,339 and 2,993, respectively. The C55γ peptide did not appear to be a lantibiotic, nor did it augment the inhibitory activities of staphylococcin C55α and/or C55β. Plasmids of 2.5 and 32.0 kb are present in strain C55, and following growth of this strain at elevated temperature (42°C), a large proportion of the progeny failed to produce strong bacteriocin activity and also lost the 32.0-kb plasmid. Protoplast transformation of these bacteria with purified 32-kb plasmid DNA regenerates the ability to produce the strong bacteriocin activity. 相似文献
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A single lineage of r2 retrotransposable elements is an active, evolutionarily stable component of the Drosophila rDNA locus 总被引:1,自引:0,他引:1
R2 elements are non-long-terminal-repeat (non-LTR) retrotransposons that
insert specifically in the 28S rRNA genes of many insects. Previous reports
concerning this element in the genus Drosophila have suggested that R2
elements are absent from many species of this genus, particularly those
species from the subgenus Drosophila. In this report, we present an
extensive study of the distribution and evolution of R2 elements in
Drosophila. A PCR survey of 59 species from 23 species groups of the two
major Drosophila subgenera found that R2 elements are present in all but
two species of the melanogaster species subgroup. Phylogenetic analysis
based on partial nucleotide sequences of R2 elements from 23 species
demonstrates that the relationships of R2 elements are congruent with those
of the Drosophila species phylogeny, suggesting that these elements have
been vertically inherited since the divergence of this genus some 60 MYA.
Sequence variation between different copies of R2 elements within each
species was less than 0.16%, indicating that these elements are undergoing
concerted evolution similar to that of the 28S genes. Several properties of
the R2 sequences suggest that these elements depend on retrotransposition
in addition to simple recombination to remain within the rDNA locus: the
rates of synonymous substitutions averaged 4.8 times the rate of
replacement substitutions, 82 of 83 R2 copies partially sequenced contained
intact open reading frames, and, finally, length variation associated with
the poly(A) 3' tails indicated that many R2 copies are the direct result of
retrotransposition.
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Shomari DL Zack-Williams Peter E Butler Deepak M Kalaskar 《World journal of stem cells》2015,7(1):51-64
Unlike central nervous system neurons; those in the peripheral nervous system have the potential for full regeneration after injury. Following injury, recovery is controlled by schwann cells which replicate and modulate the subsequent immune response. The level of nerve recovery is strongly linked to the severity of the initial injury despite the significant advancements in imaging and surgical techniques. Multiple experimental model shave been used with varying successes to augment the natural regenerative processes which occur following nerve injury. Stem cell therapy in peripheral nerve injury may be an important future intervention to improve the best attainable clinical results. In particular adipose derived stem cells(ADSCs) are multipotent mesenchymal stem cells similar to bone marrow derived stem cells, which are thought to have neurotrophic properties and the ability to differentiate into multiple lineages. They are ubiquitous within adipose tissue; they can form many structures resembling the mature adult peripheral nervous system. Following early in vitro work; multiple small and large animal in vivo models have been used in conjunction with conduits, autografts and allografts to successfully bridge the peripheral nerve gap. Some of the ADSC related neuroprotective and regenerative properties have been elucidated however much work remains before a model can be used successfully in human peripheral nerve injury(PNI). This review aims to provide a detailed overview of progress made in the use of ADSC in PNI, with discussion on the role of a tissue engineered approach for PNI repair. 相似文献
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Lathe WC rd; Burke WD; Eickbush DG; Eickbush TH 《Molecular biology and evolution》1995,12(6):1094-1105
R1 is a non-long terminal repeat (non-LTR) retrotransposable element that
inserts into a specific sequence of insect 28S ribosomal RNA genes. We have
previously shown that this element has been maintained through vertical
transmission in the melanogaster species subgroup of Drosophila. To address
whether R1 elements have been vertically transmitted for longer periods of
evolutionary time, the analysis has been extended to 11 other species from
four species groups of the genus Drosophila (melanogaster, obscura,
testecea, and repleta). All sequenced elements appeared functional on the
basis of the preservation of their open-reading frames and consistently
higher rate of substitution at synonymous sites relative to replacement
sites. The phylogenetic relationships of the R1 elements from all species
analyzed were congruent with the species phylogenies, suggesting that the
R1 elements have been vertically transmitted since the inception of the
Drosophila genus, an estimated 50-70 Mya. The stable maintenance of R1
through the germ line appears to be the major mechanism for the widespread
distribution of these elements in Drosophila. In two species, D.
neotestecea of the testecea group and D. takahashii of the melanogaster
group, a second family of R1 elements was also present that differed in
sequence by 46% and 31%, respectively, from the family that was congruent
with the species phylogeny. These second families may represent occasional
horizontal transfers or, alternatively, they could reflect the ability of
R1 elements to diverge into new families within a species and evolve
independently.
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