Growth Temperature (growth + temperature)

Distribution by Scientific Domains

Kinds of Growth Temperature

  • high growth temperature
  • low growth temperature
  • optimal growth temperature


  • Selected Abstracts


    Influence of Growth Temperature and Carrier Flux on the Structure and Transport Properties of Highly Oriented CrO2 on Al2O3 (0001),

    CHEMICAL VAPOR DEPOSITION, Issue 10 2007
    M. Sousa
    Abstract In this work we report on the structure and magnetic and electrical transport properties of CrO2 films deposited onto (0001) sapphire by atmospheric pressure (AP)CVD from a CrO3 precursor. Films are grown within a broad range of deposition temperatures, from 320 to 410,C, and oxygen carrier gas flow rates of 50,500,sccm, showing that it is viable to grow highly oriented a -axis CrO2 films at temperatures as low as 330,C i.e., 60,70,C lower than is reported in published data for the same chemical system. Depending on the experimental conditions, growth kinetic regimes dominated either by surface reaction or by mass-transport mechanisms are identified. The growth of a Cr2O3 interfacial layer as an intrinsic feature of the deposition process is studied and discussed. Films synthesized at 330,C keep the same high quality magnetic and transport properties as those deposited at higher temperatures. [source]


    Psychrotolerant and microaerophilic bacteria in boreal groundwater

    FEMS MICROBIOLOGY ECOLOGY, Issue 1 2002
    M.K. Mnnist
    Abstract Growth temperature and microaerophily of 39 phylogenetically different isolates from boreal oxygen-deficient groundwater were studied. Based on growth temperatures, the isolates were mainly psychrotolerant bacteria as 35 grew at 2C and only three at 35C. Growth rates in the range of 4,35C fitted the Ratkowsky square root model well. Optimum temperatures of the groundwater isolates varied between 18 and 30C. In semisolid glucose and PYGV media, 59% and 28% of the isolates, respectively, preferred microaerophilic growth and 33% were catalase-negative. The microaerophilic isolates had the highest sensitivity to H2O2 whereas sensitivity to the superoxide generator paraquat was similar among microaerophilic and aerobic isolates. The results show that the cold (6,8C) and oxygen-deficient groundwater harbors psychrotolerant and microaerophilic bacteria of different phylogenetic origins which are well adapted to their environment. [source]


    Growth of single-grain GdBa2Cu3O7-x superconductors by top seeded infiltration and growth technique

    CRYSTAL RESEARCH AND TECHNOLOGY, Issue 3 2010
    Guo-Zheng Li
    Abstract The top seeded infiltration and growth technique (TSIG) is an effective way for the preparation of bulk REBa2Cu3O7-x (RE-123, where RE denotes rare earth) with finely dispersed RE2BaCuO5 (RE-211) particles compared to the conventional melt growth (MG) method. The nucleation temperature and the ending growth temperature are the most important parameters need to be optimized during the preparation of RE-123 bulks by the TSIG process. In this paper, the effects of these parameters on the growth of single-grain GdBa2Cu3O7-x (GdBCO) superconductors have been investigated experimentally. It is found that the temperature for the growth of single-grain GdBCO is in the region between 1040 C and 1015 C. In addition, the relation between growth rate and supercooling has been investigated in detail. The combined techniques of SEM and EDS were used to study the microstructure of the samples grown at different temperatures. Based on this, a two-step slow cooling method during the crystallization process is proposed for the fabrication of RE-123 bulks. Finally, the single-grain GdBCO samples of the diameters 20 mm and 30 mm were fabricated successfully by the TSIG technique, with the slow-cooling process in the temperature window 1030 C,1020 C for 60 h and 100 h respectively. ( 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Growth of YCOB single crystals by flux technique and their characterization

    CRYSTAL RESEARCH AND TECHNOLOGY, Issue 5 2008
    R. Arun Kumar
    Abstract Nonlinear optical single crystals of YCOB with good optical quality were grown by the flux technique for the first time. Polycrystalline YCOB samples were synthesized by solid state reaction method. The thermal analysis of the sample was performed with lithium carbonate flux in different weight proportions and the growth temperature was optimised. Single crystals of YCOB with dimensions 3 3 5 mm3 were obtained by the method of ,slow-cooling'. The grown crystals were characterized by XRD, UV-VIS-NIR, EDAX, FTIR and etching studies. The powder XRD pattern revealed the formation of YCOB compound. The lattice parameters were identified through single crystal XRD studies. The UV-VIS-NIR results showed that the crystal has a sharp cutoff at 220 nm and is nearly 55% transparent over a wide wavelength range enabling applications in the UV region. The EDAX measurement revealed the ,flux-free' crystal formation. The presence of the functional groups belonging to the YCOB crystals was identified by the FTIR results. ,Hillock-like' patterns are observed in the etching studies. The primary emphasis in this study is laid to describe ,flux technique' as an alternative method to grow YCOB crystals. The results are presented and discussed. ( 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Growth of big single crystals of a new magnetic superconducting double perovskite Ba2PrRu1,xCuxO6

    CRYSTAL RESEARCH AND TECHNOLOGY, Issue 2 2006
    S. M. Rao
    Abstract Single crystals of Ba2PrRu1,xCuxO6 with x = 0 to 0.2, have been grown from high temperature solutions of a mixture of PbO-PbF2 in the temperature range 1100,1200 C. Thin crystals with mostly a hexagonal and triangular plate like habit measuring up to 1,2 mm across and 0.1,0.2 mm thick were obtained. The size, quality and morphology of the crystals were improved by varying the solution volume as well as additives like B2O3. Large crystals measuring up to 3 mm across and 0.3 to 0.5 mm thick were obtained with 5,7 wt% solute concentration and 0.51 wt% of B2O3. The ZFC curves exhibit a spin glass like behavior with x = 0 and a superconducting transition at 8 to 11 K depending on x = 0.05 to 0.1. The transition was also influenced by the growth temperature and post growth annealing. Powder x-ray diffraction, EDS and Raman spectroscopic measurements confirm the presence of Cu in the crystals. ( 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Growth of lead bromide polycrystalline films

    CRYSTAL RESEARCH AND TECHNOLOGY, Issue 10 2004
    M. Giles
    Abstract Lead bromide polycrystalline films were grown by the physical vapor deposition method (PVD). Glass 1,x1, in size, uncoated, and coated with Indium Tin Oxide (ITO), was used as substrate and rear contact. The starting material was evaporated at temperatures from 395C to 530C under high vacuum atmosphere (6 x 10 -3 Pa) and during 8 days. The substrate temperature was prefixed from 190C to 220C. Film thickness yielded values from 40 to 90 ,m. Optical microscopy and scanning electron microscopy (SEM) were performed on the films. Grain size resulted to be from 1.0 to 3.5 ,m. SEM and X-ray diffraction indicate that films grow with a preferred orientation with the (0 0 l) planes parallel to the substrate. The Texture Coefficient (TC) related to the plane (0 0 6) was 7.3. Resistivity values in the order of 1012 ,cm were obtained for the oriented samples, but a strong polarization indicates severe charge transport problems in the films. Film properties were correlated with the growth temperature and with previous results for films of other halides. ( 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    A novel thermostable hemoglobin from the actinobacterium Thermobifida fusca

    FEBS JOURNAL, Issue 16 2005
    Alessandra Bonamore
    The gene coding for a hemoglobin-like protein (Tf-trHb) has been identified in the thermophilic actinobacterium Thermobifida fusca and cloned in Escherichia coli for overexpression. The crystal structure of the ferric, acetate-bound derivative, was obtained at 2.48 resolution. The three-dimensional structure of Tf-trHb is similar to structures reported for the truncated hemoglobins from Mycobacterium tuberculosis and Bacillus subtilis in its central domain. The complete lack of diffraction patterns relative to the N- and C-terminal segments indicates that these are unstructured polypeptides chains, consistent with their facile cleavage in solution. The absence of internal cavities and the presence of two water molecules between the bound acetate ion and the protein surface suggest that the mode of ligand entry is similar to that of typical hemoglobins. The protein is characterized by higher thermostability than the similar mesophilic truncated hemoglobin from B. subtilis, as demonstrated by far-UV CD melting experiments on the cyano-met derivatives. The ligand-binding properties of Tf-trHb, analyzed in stopped flow experiments, demonstrate that Tf-trHb is capable of efficient O2 binding and release between 55 and 60 C, the optimal growth temperature for Thermobifida fusca. [source]


    Phylogeny of cyclic nitramine-degrading psychrophilic bacteria in marine sediment and their potential role in the natural attenuation of explosives

    FEMS MICROBIOLOGY ECOLOGY, Issue 3 2004
    Jian-Shen Zhao
    Abstract Previously we reported on in situ mineralization of cyclic nitramine explosives including hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) in marine sediment from Halifax Harbour. In the present study, we isolated several novel psychrophilic bacteria from the sediment with optimal growth temperature at 10 or 15 C. Phylogenetic analysis of their 16S rRNA genes identified the isolates as members of the gamma and delta subdivisions of Proteobacteria, Fusobacteria and Clostridiales. The isolates mineralized 3.7,45.2% of RDX (92 ,M) in 82 days of incubation at 10 C under oxygen-limited or anaerobic conditions with the gamma subdivision isolates demonstrating the highest mineralization (45.2% of total C). Removal of RDX by all isolates was accompanied by the formation of all three nitroso derivatives, with the mono nitroso derivative (MNX) being the major one. Isolates of the delta proteobacteria and Fusobacteria removed HMX with concurrent formation of the mononitroso derivative (NO-HMX). Using resting cells of isolates of the gamma subdivision, methylenedinitramine (MEDINA) and 4-nitro-2,4-diazabutanal (NDAB) were detected, suggesting ring-cleavage following denitration of either RDX and/or its initially reduced product, MNX. These results clearly demonstrate that psychrophilic bacteria capable of degrading cyclic nitramines are present in the marine sediment, and might contribute to the in situ biodegradation and natural attenuation of the chemicals. [source]


    A combined stress response analysis of Spirulina platensis in terms of global differentially expressed proteins, and mRNA levels and stability of fatty acid biosynthesis genes

    FEMS MICROBIOLOGY LETTERS, Issue 2 2008
    Wattana Jeamton
    Abstract Changes in gene expression play a critical role in enhancing the ability of cyanobacteria to survive under cold conditions. In the present study, Spirulina platensis cultures were grown at the optimal growth temperature, in the light, before being transferred to dark conditions at 22 C. Two dimensional-differential gel electrophoresis was then performed to separate differentially expressed proteins that were subsequently identified by MS. Among all differentiated proteins identified, a protein involved in fatty acid biosynthesis, (3R)-hydroxymyristoyl-[acyl-carrier-protein]-dehydratase encoded by fabZ, was the most up-regulated protein. However, the fatty-acid desaturation proteins were not significantly differentiated. This raised the question of how the unsaturated fatty acid, especially ,-linolenic acid, content in the cells in the cold,dark shift remained stable compared with that of the cold shift. Thus, a study at the transcriptional level of these desaturase genes, desC, desA and desD, and also of the fabZ gene was conducted. The results indicated that in the dark, where energy is limited, mRNA stability was enhanced by exposure to low temperatures. The data demonstrate that when the cells encounter cold stress with energy limitation, they can maintain their homeoviscous adaptation ability via mRNA stability. [source]


    Phylogeographic variation among isolates of the Sirococcus conigenus P group

    FOREST PATHOLOGY, Issue 1 2007
    H. Konrad
    Summary In this study the phylogeographic variation among isolates of the Sirococcus conigenus P group and the phylogenetic relationships of S. conigenus with Sirococcus clavigignenti-juglandacearum and other species previously placed in the genus Sirococcus were investigated. A collection of 33 isolates originating from Picea, Pinus and Larix in Europe, North America and Bhutan were characterized by sequence analyses of the internal transcribed spacer (ITS) region (including ITS1, 5.8S ribosomal DNA, ITS2) of the nuclear rDNA and a portion of the , -tubulin gene. In phylogenetic analyses most isolates from pine, spruce and larch formed a distinct clade, representing the P group of S. conigenus, which was separated from the T group of this pathogen. Four isolates from Picea in Europe and Canada formed a third clade within S. conigenus and these isolates are referred to as the S group. The P group consisted of five distinct ITS haplotypes, which partly differed in their optimum growth temperature and their growth rates at 25C on malt extract agar. Nested clade analysis resolved the five haplotypes into three distinct clades and revealed significant genetic/geographic associations for some of the haplotypes. Parsimony analysis of the small subunit (18S) ribosomal DNA sequences confirmed the phylogenetic affinities between S. conigenus and S. clavigignenti-juglandacearum. In contrast, Godronia cassandrae and Hormococcus conorum, which formerly had been placed in the genus Sirococcus, were found to be only distantly related to S. conigenus and S. clavigignenti-juglandacearum. [source]


    Metastable Copper-Phthalocyanine Single-Crystal Nanowires and Their Use in Fabricating High-Performance Field-Effect Transistors

    ADVANCED FUNCTIONAL MATERIALS, Issue 23 2009
    Kai Xiao
    Abstract This paper describes a simple, vapor-phase route for the synthesis of metastable , -phase copper-phthalocyanine (CuPc) single-crystal nanowires through control of the growth temperature. The influence of the growth temperature on the crystal structures, morphology, and size of the CuPc nanostructures is explored using X-ray diffraction (XRD), optical absorption, and transmission electron microscopy (TEM). , -CuPc nanowires are successfully incorporated as active semiconductors in field-effect transistors (FETs). Single nanowire devices exhibit carrier mobilities and current on/off ratios as high as 0.4,cm2 V,1 s,1 and >104, respectively. [source]


    Cold adaptation in geographical populations of Drosophila melanogaster: phenotypic plasticity is more important than genetic variability

    FUNCTIONAL ECOLOGY, Issue 5 2004
    A. AYRINHAC
    Summary 1According to their geographical distribution, most Drosophila species may be classified as either temperate or tropical, and this pattern is assumed to reflect differences in their thermal adaptation, especially in their cold tolerance. We investigated cold tolerance in a global collection of D. melanogaster by monitoring the time adults take to recover from chill coma after a treatment at 0 C. 2Flies grown at an intermediate temperature (21 C) showed a significant linear latitudinal cline: recovery was faster in populations living in colder climates. 3The role of growth temperature was analysed in a subset of tropical and temperate populations. In all cases, recovery time decreased when growth temperature was lowered, and linear reaction norms were observed. This adaptive phenotypic plasticity explained more than 80% of the total variation, while genetic latitudinal differences accounted for less than 4%. 4The beneficial effect observed in adults grown at a low temperature contrasts with other phenotypic effects which, like male sterility, appear as harmful and pathological. Our results point to the difficulty of finding a general interpretation to the diversity of plastic responses that are induced by growth temperature variations. [source]


    Growth and physiological acclimation to temperature and inorganic carbon availability by two submerged aquatic macrophyte species, Callitriche cophocarpa and Elodea canadensis

    FUNCTIONAL ECOLOGY, Issue 2 2000
    B. Olesen
    Abstract 1.,Interactive effects of temperature and inorganic carbon availability on photosynthetic acclimation and growth of two submerged macrophyte species, Elodea canadensis and Callitriche cophocarpa, were examined to test the hypotheses that: (1) effects of temperature on growth rate and photosynthetic acclimation are suppressed under low inorganic carbon availability; (2) the plants compensate for the reduction in activity of individual enzymes at lower temperatures by increasing the activity per unit plant mass, here exemplified by Rubisco. The experiments were performed in the laboratory where plants were grown in a factorial combination of three temperatures (7,25 C) and three inorganic carbon regimes. 2.,The relative growth rate of both species was strongly affected by growth conditions and increased by up to 45 times with increased temperature and inorganic carbon availability. The sensitivity to inorganic carbon was greatest at high temperature and the sensitivity to temperature greatest at high carbon concentrations. 3.,Photosynthetic acclimation occurred in response to growth conditions for both species. The affinity for inorganic carbon and the photosynthetic capacity, both measured at 15 C, increased with reduced inorganic carbon availability during growth and were greater at warmer than at cooler growth temperature. The acclimative change in photosynthesis was related to the extent of temperature and inorganic carbon stress. Using data for Elodea, a negative relationship between degree of temperature stress and photosynthetic performance was found. In relation to inorganic carbon, a linear increase in CO2 affinity and photosynthetic capacity was found with increased inorganic carbon stress during growth. 4.,The total Rubisco activity declined with increased inorganic carbon availability during growth and with enhanced growth temperature. In addition, the activation state of Rubisco was higher at cooler than at warmer temperatures for Callitriche. This suggests that low-temperature grown plants compensate for the temperature-dependent reduction in activity of the individual Rubisco molecules by enhancing resource allocations towards Rubisco. [source]


    Increased Interface Strength in Carbon Fiber Composites through a ZnO Nanowire Interphase

    ADVANCED FUNCTIONAL MATERIALS, Issue 16 2009
    Yirong Lin
    Abstract One of the most important factors in the design of a fiber reinforced composite is the quality of the fiber/matrix interface. Recently carbon nanotubes and silicon carbide whiskers have been used to enhance the interfacial properties of composites; however, the high growth temperature degrade the fiber strength and significantly reduce the composite's in-plane properties. Here, a novel method for enhancing the fiber/matrix interfacial strength that does not degrade the mechanical properties of the fiber is demonstrated. The composite is fabricated using low-temperature solution-based growth of ZnO nanowires on the surface of the reinforcing fiber. Experimental testing shows the growth does not adversely affect fiber strength, interfacial shear strength can be significantly increased by 113%, and the lamina shear strength and modulus can be increased by 37.8% and 38.8%, respectively. This novel interface could also provide embedded functionality through the piezoelectric and semiconductive properties of ZnO. [source]


    Atomic Layer Deposition of UV-Absorbing ZnO Films on SiO2 and TiO2 Nanoparticles Using a Fluidized Bed Reactor,

    ADVANCED FUNCTIONAL MATERIALS, Issue 4 2008
    David M. King
    Atomic layer deposition (ALD) was used to apply conformal, nanothick ZnO coatings on particle substrates using a fluidized bed reactor. Diethylzinc (DEZ) and water were used as precursors at 177,C. Observed growth rates were ca. 2.0 /cycle on primary particles as verified by HRTEM. ICP-AES and XPS were used to quantify Zn:substrate ratios. Layers of 6, 18, and 30 nm were deposited on 550 nm SiO2 spheres for UV blocking cosmetics particles. TiO2 nanoparticles were coated in the second part of this work by ZnO shells of 2, 5, and 10 nm thickness as novel inorganic sunscreen particles. The specific surface area of powders changed appropriately after nanothick film deposition using optimized conditions, signifying that high SA particles can be functionalized without agglomeration. The ZnO layers were polycrystalline as deposited and narrowing of the FWHM occurred upon annealing. Annealing the ZnO-TiO2 nanocomposite powder to 600,C caused the formation of zinc titanate (Zn2TiO4) in both oxygen-rich and oxygen-deficient environments. The non-ideal surface behavior of the DEZ precursor became problematic for the much longer times required for high surface area nanoparticle processing and results in Zn-rich films at this growth temperature. In situ mass spectrometry provides process control capability to functionalize bulk quantities of nano- and ultrafine particles without significant precursor waste or process overruns. ZnO overlayers can be efficiently deposited on the surfaces of primary particles using ALD processing in a scalable fluidized bed reactor. [source]


    Quantifying the heterogeneous heat response of Escherichia coli under dynamic temperatures

    JOURNAL OF APPLIED MICROBIOLOGY, Issue 4 2010
    E. Van Derlinden
    Abstract Aims:, Non-sigmoid growth curves of Escherichia coli obtained at constant temperatures near the maximum growth temperature (Tmax) were previously explained by the coexistence of two subpopulations, i.e. a stress-sensitive and a stress-resistant subpopulation. Mathematical simulations with a heterogeneous model support this hypothesis for static experiments at 45C. In this article, the behaviour of E. coli, when subjected to a linearly increasing temperature crossing Tmax, is studied. Methods and Results:, Subpopulation dynamics are studied by culturing E. coli K12 MG1655 in brain heart infusion broth in a bioreactor. The slowly increasing temperature (C h,1) starting from 42C results in growth up to 60C, a temperature significantly higher than the known Tmax. Given some additional presumptions, mathematical simulations with the heterogeneous model can describe the dynamic experiments rather well. Conclusions:, This study further confirms the existence of a stress-resistant subpopulation and reveals the unexpected growth of E. coli at temperatures significantly higher than Tmax. Significance and Impact of the Study:, The growth of the small stress-resistant subpopulation at unexpectedly high temperatures asks for a revision of currently applied models in food safety and food quality strategies. [source]


    Establishment and characterization of two new cell lines derived from flounder, Paralichthys olivaceus (Temminck & Schlegel)

    JOURNAL OF FISH DISEASES, Issue 11-12 2003
    M S Kang
    Abstract Two new cell cultures from flounder, Paralichthys olivaceus (Temminck & Schlegel), flounder fin (FFN) cells from fin tissue and flounder spleen (FSP) cells from spleen tissue, were established and characterized. The cells multiplied well in Eagle's minimum essential medium, supplemented with 10% foetal bovine serum, and have been subcultured more than 100 times, becoming continuous cell lines. Modal diploid chromosome number of FFN and FSP cells was 64 and 62, respectively. Polymerase chain reaction products were obtained from FFN and FSP cells with primer sets of microsatellite markers of flounder. Optimal growth temperature was 20 C and consisted of epithelioid cells. FFN and FSP cells showed cytopathic effects after inoculation of infectious pancreatic necrosis virus, marine birnavirus, chum salmon virus, infectious haematopoietic necrosis virus, spring viraemia of carp virus and hirame rhabdovirus. Thus these new cell lines may be useful for studying a wide range of fish viruses. [source]


    Phenotypical characteristics of Shiga-like toxin Escherichia coli isolated from sheep dairy products

    LETTERS IN APPLIED MICROBIOLOGY, Issue 3 2007
    I. Caro
    Abstract Aims: To analyse phenotypical characteristics of Shiga toxin-producing Escherichia coli (STEC) strains from ovine origin. Methods and Results: A total of 13 STEC strains (eight O157 and five non-O157) isolated from sheep dairy products were used in this study. Biochemical traits, motility, haemolytic activity, resistance to tellurite,cefixime, maximum growth temperature and antibiotic resistance were determined. The STEC strains were grouped into nine biochemical and physiological biotypes (five for the O157 and four for the non-O157 strains). All STEC strains showed resistance to bacitracin, cloxacilin, penicillin and tylosin. Conclusions: Different biotypes and antibiotic resistance patterns of STEC isolated from sheep dairy products were observed. Significance and Impact of the Study: This work will be a contribution to the better characterization of STEC isolated from sheep dairy products, which have, to date, been scarcely studied, and to the better understanding of the risks associated with its consumption. [source]


    The Cryptococcus neoformans MAP kinase Mpk1 regulates cell integrity in response to antifungal drugs and loss of calcineurin function

    MOLECULAR MICROBIOLOGY, Issue 5 2003
    Peter R. Kraus
    Summary Cell wall integrity is crucial for fungal growth, development and stress survival. In the model yeast Saccharomyces cerevisiae, the cell integrity Mpk1/Slt2 MAP kinase and calcineurin pathways monitor cell wall integrity and promote cell wall remodelling under stress conditions. We have identified the Cryptococcus neoformans homologue of the S. cerevisiae Mpk1/Slt2 MAP kinase and have characterized its role in the maintenance of cell integrity in response to elevated growth temperature and in the presence of cell wall synthesis inhibitors. C. neoformans Mpk1 is required for growth at 37C in vitro, and this growth defect is suppressed by osmotic stabilization. C. neoformans mutants lacking Mpk1 are attenuated for virulence in the mouse model of cryptococcosis. Phosphorylation of Mpk1 is induced in response to perturbations of cell wall biosynthesis by the antifungal drugs nikkomycin Z (a chitin synthase inhibitor), caspofungin (a ,-1,3-glucan synthase inhibitor), or FK506 (a calcineurin inhibitor), and mutants lacking Mpk1 display enhanced sensitivity to nikkomycin Z and caspofungin. Lastly, we show that calcineurin and Mpk1 play complementing roles in regulating cell integrity in C. neoformans. Our studies demonstrate that pharmacological inhibition of the cell integrity pathway would enhance the activity of antifungal drugs that target the cell wall. [source]


    Mechanism of membrane fluidity optimization: isothermal control of the Bacillus subtilis acyl-lipid desaturase

    MOLECULAR MICROBIOLOGY, Issue 5 2002
    Larisa E. Cybulski
    Summary The Des pathway of Bacillus subtilis regulates the expression of the acyl-lipid desaturase, Des, thereby controlling the synthesis of unsaturated fatty acids (UFAs) from saturated phospholipid precursors. Previously, we showed that the master switch for the Des pathway is a two-component regulatory system composed of a membrane-associated kinase, DesK, and a soluble transcriptional regulator, DesR, which stringently controls transcription of the des gene. Activation of this pathway takes place when cells are shifted to low growth temperature. Here, we report on the mechanism by which isoleucine regulates the Des pathway. We found that exogenous isoleucine sources, as well as its ,-keto acid derivative, which is a branched-chain fatty acid precursor, negatively regulate the expression of the des gene at 37C. The DesK,DesR two-component system mediates this response, as both partners are required to sense and transduce the isoleucine signal at 37C. Fatty acid profiles strongly indicate that isoleucine affects the signalling state of the DesK sensor protein by dramatically increasing the incorporation of the lower-melting-point anteiso-branched-chain fatty acids into membrane phospholipids. We propose that both a decrease in membrane fluidity at constant temperature and a temperature downshift induce des by the same mechanism. Thus, the Des pathway would provide a novel mechanism to optimize membrane lipid fluidity at a constant temperature. [source]


    Growth phase-dependent expression and degradation of histones in the thermophilic archaeon Thermococcus zilligii

    MOLECULAR MICROBIOLOGY, Issue 4 2000
    Marcel E. Dinger
    HTz is a member of the archaeal histone family. The archaeal histones have primary sequences and structural similarity to the eukaryal histone fold domain, and are thought to resemble the archetypal ancestor of the eukaryal nucleosome core histones. The effects of growth phase on the total soluble proteins from Thermococcus zilligii, isolated after various stages of growth from mid-logarithmic to late stationary phase, were examined by denaturing polyacrylamide gel electrophoresis. On entry into stationary phase, at least 11 proteins were detected that changed considerably in level. One of these proteins was identified by Western hybridization as HTz. The level of HTz decreased dramatically as cells entered stationary phase, and it could not be detected by late stationary phase. Unexpectedly, the Western hybridization detected a second protein, with an estimated molecular mass of approximately 14 kDa, which paralleled the decrease in level of HTz. Native purified HTz was shown to retain complete activity after prolonged incubation at the growth temperature of the organism, suggesting that the decrease in HTz was a specific cell-regulated process. Analysis of native purified HTz by electrospray ionization mass spectrometry revealed the molecular masses of HTz1 and HTz2 to be 7204 3 Da and 7016 3 Da respectively. The only non-covalent species that was detected corresponded to the molecular mass of an HTz1,HTz2 heterodimer. Northern analyses of T. zilligii total RNA with an htz1 gene probe indicated a rapid decrease in expression of htz1 with progression of the growth phase, and complete repression of htz1 transcript synthesis by late logarithmic phase. Three proteins that changed in level with growth phase were identified by N-terminal sequence analysis. The first was homologous to a hypothetical protein conserved in all Archaea sequenced to date, the second to the Sac10b family of archaeal DNA-binding proteins and the third to the C-terminal region of the leucine-responsive regulatory family of DNA-binding proteins (LRPs). [source]


    Environmental regulation of recA gene expression in Porphyromonas gingivalis

    MOLECULAR ORAL MICROBIOLOGY, Issue 3 2001
    Y. Liu
    The recA gene product in Porphyromonas gingivalis is involved in DNA repair. Further, disruption of this gene can affect the proteolytic activity and expression of other virulence factors in this organism. Since several known environmental factors can influence virulence gene expression in P. gingivalis, we investigated the influence of these signals on the expression of the recA gene in this organism. A heterodiploid strain of P. gingivalis (designated FLL118) containing a transcriptional fusion of the recA promoter region and the promoterless tetracycline-resistant gene [tetA(Q)2] and xylosidase/arabinosidase (xa) gene cassette was constructed. The recA promoter activity was assessed by measurement of xylosidase activity in FLL118. The expression remained relatively constant during different growth phases, at different pH levels and in the presence of DNA-damaging agents. In response to hemin limitation and in the presence of calcium there was a moderate increase in recA promoter activity. Temperature also affected the expression. The highest level of xylosidase activity was observed in cultures at 32C with a decline of approximately 46% as growth temperature increased to 41C. Reverse transcriptase polymerase chain reaction analysis revealed that this regulation may be occurring at the transcriptional level. These results suggest that expression of the recA gene in P. gingivalis W83 is responsive to several environmental signals but is not regulated by a DNA damage,inducible SOS-like regulatory system. [source]


    Effects of temperature and pH on growth and photosynthesis of the thermophilic cyanobacterium Synechococcus lividus as measured by pulse-amplitude modulated fluorometry

    PHYCOLOGICAL RESEARCH, Issue 4 2006
    Chung-Ching Liao
    SUMMARY In this study, the effects of five different temperatures and pH conditions on growth and photosynthetic performance of Synechococcus lividus Copeland from Taiwan were monitored in the field and the laboratory by using an underwater pulse-amplitude modulated (Diving-PAM) fluorometer. In the field, the optimal growth temperature of S. lividus was found to be 57C. Such a finding was congruent with the growth rate in the laboratory culture, in which the optimal growth temperatures ranged from 45 to 60C. In photosynthetic performance, the light-saturated maximum relative electron transport rate (ETRmax) and the light-limited slope (,ETR) exhibited highest values at 50C. At five different pH conditions, higher ETRmax and ,ETR were observed from pH 7 to 9. In addition, regression analysis demonstrated a significant positive relationship between the growth rate and the ETRmax values (R2 = 0.9527), indicating that the growth of S. lividus was largely restricted to its photosynthetic performance. In conclusion, the photosynthetic performance and growth of the thermophilic cyanobacterium S. lividus were sensitive to fluctuations in temperature but not in pH. The present investigation offers a better understanding of the photosynthetic physiology. [source]


    Low-temperature growth of high quality AlN films on carbon face 6H-SiC

    PHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 1 2008
    Myunghee Kim
    Abstract AlN films have been grown on atomically flat carbon face 6H-SiC (000) substrates by pulsed laser deposition and their structural properties have been investigated. In-situ reflection high-energy electron diffraction observations have revealed that growth of AlN at 710 C proceeds in a Stranski,Krastanov mode, while typical layer-by-layer growth occurs at room temperature (RT) with atomically flat surfaces. It has been revealed that the crystalline quality of the AlN film is dramatically improved by the reduction in growth temperature down to RT and the full width at half maximum values in the X-ray rocking curves for 0004 and 102 diffractions of the RT-grown AlN film are 0.05 and 0.07, respectively. X-ray reciprocal space mapping has revealed that the introduction of misfit dislocations is suppressed in the case of RT growth, which is probably responsible for the improvement in crystalline quality. ( 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Effect of growth parameters on the formation of three-dimensional InAs islands on (001) silicon substrate

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 2 2010
    J. Y. Lim
    Abstract The purpose of this work is to find optimal conditions for the growth of three-dimensional (3D) InAs islands on (2,,1) (001) Si substrate using modified Stranski,Krastanow (S,K) method. From the analysis of atomic-force-microscopy (AFM) images and reflection-high-energy-electron-diffraction (RHEED) patterns, we have found that InAs islands can be grown on Si when the growth temperature is in the range of 370,430,C and also when In-injection of more than three periods is used. At the growth temperature of 390,C and In-injection of four periods, uniform distribution of islands with the highest density of about 600,/m2 were obtained. The average width and height of these islands were 36.1,,9.2,nm and 6.2,,2.0,nm, respectively. [source]


    Nitride-based quantum structures and devices on modified GaN substrates

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2009
    Piotr Perlin
    Abstract We have studied the properties of InGaN layers and quantum wells grown on gallium nitride substrates with intentional surface misorientation with respect to its crystalline c -axis. Misorientation varied in the range from 0 up to 2 degree. The indium content was changed by using the different growth temperature (between 750 C and 820 C) during metalorganic vapor phase epitaxy. With increasing misorientation angle the average indium content decreased significantly. This effect was accompanied by the strong increase of the emission line bandwidth suggesting more pronounced indium segregation. The results of cathodoluminescence measurements show that these effects correspond to different number of atomic steps/terraces existing on the surface of gallium nitride substrate. Very interesting result is also demonstrated concerning p-type GaN layers. With increasing misorientation, the free hole density drastically increases above 1018 cm,3. This improvement in p-type doping is not related to the increased Mg concentration but to the reduction in the compensating donor density. Using this advantage we demonstrate nitride light emitters with improved electrical properties. ( 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Growth behavior and microstructure of ZnO epilayer on ,-LiAlO2(100) substrate by chemical vapor deposition

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 2 2009
    Liuwen Chang
    Abstract Low lattice-mismatched ,-LiAlO2(100) substrates were employed to grow ZnO epitaxial films by chemical vapor deposition. The influence of growth temperature on growth behavior of ZnO was investigated. Results indicated that the low lattice-matched (100) crystallites nucleate on substrate at all growth temperatures employed. However, a second type of crystallites having an (0001) orientation can also nucleate on substrate at low growth temperature of 575 C and 640 C. The growth rate of the later crystallite is, however, higher than that of the (100) one and finally results in a single crystalline ZnO film having an [0001] azimuthal orientation. ( 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    TEM investigations of (In,Ga)N/GaN quantum structures

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 11 2008
    P. Manolaki
    Abstract The paper reports on the influence of the growth temperature on the structural and chemical properties of (In,Ga)N quantum wells (QWs) on GaN. Two different samples A and B were fabricated. The QWs of the sample A were grown at a constant temperature of 600 C. For the QWs of the sample B the temperature was 530 C, while for the GaN barrier it was raised to 600 C. The chemical and structural properties were studied by electron diffraction contrast imaging using the 0001 and 0002 reflection, respectively. Sample A exhibits homogeneous (In,Ga)N QWs. For sample B some undulated strain contrast of the QWs is visible hinting to the formation of quantum dots (QDs). The self-organisation of (In,Ga)N QDs in sample B is also evidenced by composition sensitive STEM-HAADF imaging, where the individual (In,Ga)N layers exhibit inhomogeneous intensity as well as varied thickness. Moreover, energy dispersive X-ray spectroscopy yielded enrichment of indium at QD sites. ( 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    MOVPE of InN films on GaN templates grown on sapphire and silicon(111) substrates

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2008
    Muhammad Jamil
    Abstract This paper reports the study of MOVPE of InN on GaN templates grown on sapphire and silicon(111) substrates. Thermodynamic analysis of MOVPE of InN performed using NH3 as nitrogen source and the experimental findings support the droplet-free epitaxial growth of InN under high V/III ratios of input precursors. At a growth pressure of 500 Torr, the optimum growth temperature and V/III ratio of the InN film are 575,650 C and >3 105, respectively. The surface RMS roughness of InN film grown GaN/sapphire template is ,0.3 nm on 2 ,m 2 ,m area, while the RMS roughness of the InN film grown on GaN/Si (111) templates is found as ,0.7 nm. The X-ray diffraction (XRD) measurement reveals the (0002) texture of the InN film on GaN/sapphire template with a FWHM of 281 arcsec of the InN (0002) , rocking curve. For the film grown on GaN/Si template under identical growth conditions, the XRD measurements show the presence of metallic In, in addition to the (0002) orientation of InN layer. ( 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Strain and wafer curvature of 3C-SiC films on silicon: influence of the growth conditions

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 4 2007
    M. Zielinski
    Abstract We study the influence of the growth conditions on the residual strain and related optical and structural properties in the case of 3C-SiC films grown on (001) silicon substrates. We show that two possible mechanisms compete to manage the final sample bow: one is by controlling the composition of the gaseous phase (C/Si ratio) the other one by adjusting the growth temperature and duration (creep effect). In both cases, we compare the low temperature photoluminescence spectra of samples grown under tensile or compressive final stress. We show that better results can be obtained when using the creep effect. ( 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]