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81.
Summary The effect of glucose and ammonium sulfate concentration on the kinetics of lactic acid formation by a heterogeneous mixed culture was evaluated by the sole product formation using the Gompertz model, which can be used to define culture media composition taking into account product accumulation and acidification rate constant. A compromise between ionic inhibition and nitrogen limitation was found by using ammonium sulfate as nitrogen source. The sugar tolerance was similar to that in exenic cultures. 相似文献
82.
Preparation of megabase-sized tomato DNA and separation of large restriction fragments by field inversion gel electrophoresis (FIGE) 总被引:4,自引:0,他引:4
The Schwartz and Cantor technique for releasing and fractionating megabase-sized DNA from agarose-embedded cells is beginning to bridge the gap in resoluation between classical genetics and current molecular DNA techniques, particularly in mammalian systems. As yet no conditions have been described for preparing plant DNA that is of sufficient length to allow similar long-range restriction mapping experiments in plant systems. In this report, we describe the application of the Schwartz and Cantor technique for preparing high molecular weight DNA from embedded tomato leaf protoplasts, as well as conditions for generating and fractionating large restriction fragments, by field inversion gel electrophoresis (FIGE). The bulk of DNA released from lysed protoplasts was at least 2 Mb in size and amenable to restriction digestion as shown by hybridizing Southern blots with, among others, a probe for the Adh-2 gene of tomato. Restriction fragments as large as 700 kb were detected. Chloroplast DNA is isolated intact, amenable to restriction analysis and, in its native form, not mobile in FIGE. 相似文献
83.
84.
José Edmundo Nava Saucedo Jean-Noël Barbotin Daniel Thomas 《Applied microbiology and biotechnology》1989,30(3):226-233
Summary The continuous production of gibberellic acid with immobilized mycelia of Gibberella fujikuroi was maintained over a hundred days in a tubular fixed-bed reactor. Free mycelium at the beginning of the storage phase was harvested from G. fujikuroi shake-flask culture and was immobilized by ionotropic gelation in calcium alginate beads.The continuous recycle production system consisted of a fixed-bed reactor, a container in which the culture medium was heated, stirred and aerated, and valves for sample withdrawal or reactant addition during the first 1320 h (55 days). A two-phase continuous extractor was then added for the last 960 hours (40 days). Free and immobilized mycelium shake-flask cultures with the same strain used in the continuous culture system were also realized to compare growth, maintenance and production parameters. The results show about the same gibberellic acid productivity in both free and immobilized mycelium shakeflask cultures: 0.384 and 0.408 mgGA3·gBiomass-1 ·day-1, respectively, whereas in the continuous system the gibberellic acid production is about twice as large for a similar biomass: 0.768 mgGA3·gBiomass-1·day-1. Several factors affecting the overall productivity of the immobilized systems were found to be: the quality and the quantity of mycelia in the biocatalyst beads and the immobilization conditions. 相似文献
85.
86.
It is generally accepted that during fast growth of Escherichia coli, the time (D) between the end of a round of DNA replication and cell division is constant. This concept is not consistent with the fact that average cell mass of a culture is an exponential function of the growth rate, if it is also accepted that average cell mass per origin of DNA replication (Mi) changes with growth rate and negative exponential cell age distribution is taken into account. Data obtained from cell composition analysis of E. coli OV-2 have shown that not only (Mi) but also D varied with growth rate at generation times () between 54 and 30 min. E. coli OV-2 is a thymine auxotroph in which the replication time (C) can be lengthened, without inducing changes in , by growth with limiting amounts of thymine. This property has been used to study the relationship between cell size and division from cell composition measurements during growth with different amounts of thymine. When C increased, average cell mass at the end of a round of DNA replication also increased while D decreased, but only the time lapse (d) between the end of a replication round and cell constriction initiation appeared to be affected because the constriction period remained fairly constant. We propose that the rate at which cells proceed to constriction initiation from the end of replication is regulated by cell mass at this event, big cells having shorter d times than small cells.Abbreviations OD450 and OD630
Optical density at a given wavelength in nm
Dedicated to Dr. John Ingraham to honor him for his many contributions to Science 相似文献
87.
Francisco Javier Caballero Isabel Igeño Jacobo Cárdenas Francisco Castillo 《Archives of microbiology》1989,152(5):508-511
The phototrophic bacterium Rhodobacter capsulatus E1F1 assimilates ammonia and other forms of reduced nitrogen either through the GS/GOGAT pathway or by the concerted action of l-alanine dehydrogenase and aminotransferases. These routes are light-independent and very responsive to the carbon and nitrogen sources used for cell growth. GS was most active in cells grown on nitrate or l-glutamate as nitrogen sources, whereas it was heavily adenylylated and siginificantly repressed by ammonium, glycine, l-alanine, l-aspartate, l-asparagine and l-glutamine, under which conditions specific aminotransferases were induced. GOGAT activity was kept at constitutive levels in cells grown on l-amino acids as nitrogen sources except on l-glutamine where it was significantly induced during the early phase of growth. In vitro, GOGAT activity was strongly inhibited by l-tyrosine and NADPH. In cells using l-asparagine or l-aspartate as nitrogen source, a concerted induction of l-aspartate aminotransferase and l-asparaginase was observed. Enzyme level enhancements in response to nitrogen source variation involved de novo protein synthesis and strongly correlated with the cell growth phase.Abbreviations ADH
l-alanine dehydrogenase
- AOAT
l-alanine:2-oxoglutarate aminotransferase
- Asnase
l-asparaginase
- GOAT
Glycine: oxaloacetate aminotransferase
- GOGAT
Glutamate synthase
- GOT
l-aspartate: 2-oxoglutarate aminotransferase
- GS
Glutamine synthetase
- HPLC
High-Pressure Liquid Chromatography
- MOPS
2-(N-morpholino)propanesulfonic acid
- MSX
l-methionine-d,l-sulfoximine 相似文献
88.
The in situ localization of Ca2+ in stage I sporangiophores of the fungus Phycomyces blakesleeanus was achieved with the potassium pyroantimonate technique. Precipitates of calcium-antimonate were present in mitochondria, vacuoles, endoplasmic reticulum and adjacent cytoplasm, Golgi-like bodies, and nuclei but not cell walls. Material treated with the calcium chelator EGTA lacked these precipitates. The preferential localization of Ca2+ in mitochondria, endoplasmic reticulum and vacuoles suggests that these organelles modulate the level of this cation in sporangiophores of P. blakesleeanus.Abbreviations EGTA
ethyleneglycol-bis-(-aminoethyl ether) N,N, tetraacetic acid 相似文献
89.
On the solution of mathematical models of herd immunity in human helminth infections 总被引:1,自引:0,他引:1
Marco V. José 《Journal of mathematical biology》1989,27(6):707-715
The general solution of the mathematical model of herd immunity to human helminth infections recently proposed by Anderson and May [3] is obtained. The numerical solution of a more accurate biological model is indistinguishable from the corresponding exact solution of a more tractable mathematical model. Computer simulations of some particular cases of this model support the notion that both ecological and immunological factors determine the observed convex patterns of age-prevalence and age-intensity curves of human helminth infections.This work was made thanks to the advise and support of Dr. Robert M. May while the author was Postdoctoral Fellow at Princeton University 相似文献
90.
Nora Goosen Harold P. A. Horsman René G. M. Huinen Arjan de Groot Pieter van de Putte 《Antonie van Leeuwenhoek》1989,56(1):85-91
From a gene bank of theAcinetobacter calcoaceticus genome a plasmid was isolated that complements four different classes of PQQ- mutants. Subclones of this plasmid revealed that the four corresponding PQQ genes are located on a fragment of 5 kilobases. The nucleotide sequence of this 5 kb fragment was determined and by means of Tn5 insertion mutants the reading frames of the PQQ genes could be identified. Three of the PQQ genes code for proteins of Mr 29700 (gene I), Mr 10800 (gene II) and Mr 43600 (gene III) respectively. In the DNA region where gene IV was mapped however the largest possible reading frame encodes for a polypeptide of only 24 amino acids. A possible role for this small polypeptide will be discussed. Finally we show that expression of the four PQQ genes inAcinetobacter lwoffi andEscherichia coli lead to the synthesis of the coenzyme in these organisms. 相似文献