Effects of air pressure oscillation amplitude on oxygen transfer rate and biomass productivity in a solid-state fermenter

The modified sulfite oxidation method was adapted for estimation of the overall oxygen transfer rate in a pressure oscillating, solid-state fermenter. At 4.5 atm and 30 °C, the oxygen transfer rate reached 717 mmol kg^–1 initial dry matter h^–1 in this system against 37 mmol kg^–1 initial dry matter h^–1 in a static tray fermenter. At 30 °C and 3 atm, Azotobacter vinelandii grew on wheat straw and reached 4.7×10¹⁰ c.f.u. g^–1 substrate dry matter after 36 h, while only 8.2×10⁹ c.f.u. g^–1 substrate dry matter was obtained in a static tray system.     

Simple binary vectors for DNA transfer to plant cells

Summary Cosmid binary vectors for the introduction of DNA into plant cells have been constructed. These vectors are derived from the replicon of the broad host range plasmid pRK2 and contain the T-DNA border regions between which have been placed a chimaeric gene conferring resistance to kanamycin in plant cells. Appropriate restriction endonuclease targets have also been placed between the border regions. These binary vectors, in conjunction with appropriate Agrobacterium strains, are capable of delivering DNA to plant cells in cocultivation experiments with very high efficiency. The transformation frequency is shown to be somewhat dependent on the replicon used. re]19850121 rv]19850506 ac]19850513     

Retrofitting YACs for direct DNA transfer into plant cells

The utility of plant YAC libraries prepared in conventional YAC vectors would be dramatically increased if these YACs could be used directly for plant transformation. A pair of vectors that allow clones from YAC libraries to be modified (retrofitted) for plant transformation by direct DNA transfer methods, such as particle bombardment or electroporation, has been developed. Modification of the YAC is achieved in two sequential yeast transformation steps by taking advantage of the homologous recombination system in yeast. Using this approach, two plant-selectable marker genes and DNA sequence elements required for copy number amplification in yeast can be introduced into YACs present in yeast strain AB1380. The utility of these vectors is demonstrated by retrofitting YACs that contain inserts ranging in size from 80 to 700 kb. The 6- to 12-fold increase in copy number of these modified YACs facilitates the isolation of YAC DNA for direct DNA transformation methods. Retrofitted YACs were used for particle bombardment to examine the efficiency with which their large DNA inserts are transferred into plant cells. The availability of these retrofitting vectors should facilitate the transfer of YAC DNA inserts into plant cells and thus help bridge the gap between existing mapping techniques and plant transformation procedures.     

Direct DNA transfer to plant cells

A range of somatic cell and molecular techniques are now available to supplement conventional plant breeding. The introduction and expression of foreign DNA has been used to modify basic aspects of physiology and development, to introduce commercially important characteristics such as herbicide and insect resistance into plants and to insert genes suitable as dominant selectable markers for somatic hybridisation. Several techniques for direct DNA delivery are available, ranging from uptake of DNA into isolated protoplasts mediated by chemical procedures or electroporation, to injection and the use of high-velocity particles to introduce DNA into intact tissues. Direct DNA uptake is applicable to both stable and transient gene expression studies and utilises a range of vectors, including those employed for gene cloning. Although the frequency of stable transformation is low, direct DNA uptake is applicable to those plants not amenable to Agrobacterium transformation, particularly monocotyledons.     

Glycerolipid transfer for the building of membranes in plant cells

Membranes of plant organelles have specific glycerolipid compositions. Selective distribution of lipids at the levels of subcellular organelles, membrane leaflets and membrane domains reflects a complex and finely tuned lipid homeostasis. Glycerolipid neosynthesis occurs mainly in plastid envelope and endoplasmic reticulum membranes. Since most lipids are not only present in the membranes where they are synthesized, one cannot explain membrane specific lipid distribution by metabolic processes confined in each membrane compartment. In this review, we present our current understanding of glycerolipid trafficking in plant cells. We examine the potential mechanisms involved in lipid transport inside bilayers and from one membrane to another. We survey lipid transfers going through vesicular membrane flow and those dependent on lipid transfer proteins at membrane contact sites. By introducing recently described membrane lipid reorganization during phosphate deprivation and recent developments issued from mutant analyses, we detail the specific lipid transfers towards or outwards the chloroplast envelope.     

The effect of recycling on plant competitive hierarchies

Evidence from field studies suggests that some plant species enhance their persistence by reinforcing patterns of N availability through differences in litter quality. Using mathematical models of nutrient flow, we explore whether and how recycling affects plant growth, competition, and coexistence and whether it leads to positive feedbacks. Two mechanisms are considered: the ability of plants to access two forms of soil N, complex (e.g., organic) and simple (e.g., nitrate), and the effect of density-dependent limitation of growth. Except in the trivial case of limitation by N in one form without density dependence, differences in litter quality can prevent the establishment of competitors. Feedback can, conversely, facilitate the invasion of competitors. At equilibrium, the rate of decomposition does not affect the outcome of competition. Species affect their long-term persistence if they alter the fraction of nitrogen that is returned to the soil and becomes available for plant uptake. Increasing the fraction of N that is recycled favors specialists in complex nitrogen and species that suppress the growth of others at high nitrogen availability. Increasing the rate of microbial decomposition of complex nitrogen favors specialists in simple nitrogen.     

植物根水倒流的证据及意义

对根水倒流的研究进展进行了综述,分析和介绍了其存在的类型、普遍性、发生量、发生位置、生理学基础等,讨论了其在植物生理学、生态学、营养学和作物载培学等学科中的重要意义,并是其存在的问题和进一步研究的方向。     

Studies on mass transfer characteristics of a modified airlift fermenter

An approach to modify external loop airlift bioreactor is presented that examines its performance with respect to mass transfer. There are various designs of airlift fermenter [1]. In the proposed system [2] the riser has been replaced by a tube of irregular geometry, in the form of converging-diverging sections (CDT-ALF), so that better mass transfer may be obtained due to better liquid mixing caused by the bubble flow, pulsation effect and early transition to turbulence. Mass transfer characteristics of the modified airlift fermenter CDT-ALF were studied and compared with those of a conventional one, UT-ALF. Overall volumetric mass transfer coefficient,K _L a, was determined by sulfite oxidation method.K _L a was determined with respect toU _G for differenth _i. HigherK _L a was always observed in CDT-ALF compared to that in UT-ALF under any operating condition ofh _i andU _G. If theK _L a values are compared in both the systems under their optimum conditions ofh _i andU _G, CDT-ALF showed 122.5% higher values ofK _L a compared to UT-ALF. However, when both the systems were operated at the lowest experimental conditions ofU _G, thek _L a in CDT-ALF was found to be 170% higher. In UT-ALF while with the decrease ofU _G,k _L a decreased, in CDT-ALF the reverse was observed i.e. at lowU _G,K _L a was higher. However with the increase ofh _i,K _L a decreased in both the systems. To predict volumetric mass transfer coefficientK _L a, empirical correlations were developed by dimensional analysis for both the reactors. The correlations were experimentally verified to determine their reliability to predict mass transfer coefficient and the deviation was found within reasonable limit.List of abbreviations ALF Airlift Fermenter - UT-ALF Uniform Tube Airlift Fermenter - CDT-ALF Converging-diverging Tube Airlift Fermenter     

Oxygen transfer measurements during yeast fermentations in a pilot scale airlift fermenter

Measurements of oxygen transfer were made during cultivation of the yeast Saccharomyces cerevisiae in a 90–250 litre working volume concentric tube airlift fermenter. Results demonstrated that the rate of oxygen transfer varies with position in the fermenter, being higher in the riser and top-section than in the downcomer and lowest near the base of the fermenter. The time for liquid circulation was generally smaller than the time constant for oxygen transfer (1/k_La) indicating that the rate of oxygen transfer was slow compared to the rate of liquid movement. Measured dissolved oxygen concentrations therefore did not represent the equilibrium arising from the balance between the rates of oxygen transfer and oxygen depletion. Hence measuredk _L a values were not representative of local oxygen transfer conditions but instead were indicators of the rate of mass transfer the liquid flow had encountered prior to reaching the point of measurement. Generally the individual rates of oxygen transfer in the vessel were found to increase with increasing vessel height.     

Low-pressure airlift fermenter for single cell protein production: I. Design and oxygen transfer studies

The energy consumption of a fermenter constitutes a major part of the operating expense of a single cell protein process. A low-pressure airlift fermenter was designed to reduce this cost. In this new design, the fermenter broth is kept below 120 cm in depth, and air alone is employed to fulfill the need of supplying oxygen, and cooling and agitating the broth. The use of low-pressure air from air blowers instead of air compressors lowers the capital cost of air delivery and reduces the energy consumption in the fermenter section to below 1 kWh/kg protein, a saving of over 70% as compared to a conventional stirred tank fermenter. It also eliminates the investment of mechanical agitators, heat exchangers, and air compressors. Sulfite oxidation studies confirmed the design concepts.     

Xylem transfer cells in the rosette plant Hieracium floribundum

Summary Xylem transfer cells in the rhizome of Hieracium floribundum are described for the first time and several methods used in visualizing these cells are discussed. The most marked wall ingrowths occur in transfer cells associated with the xylem of foliar traces.This research was supported by an NRC of Canada grant to Dr. R. L. Peterson.Undergraduate student and Associate Professor, resp.     

Development and application of the thin channel rectangular air lift mass transfer reactor to fermentation and waste-water treatment systems

The consideration of fermentation principles in the treatment of industrial and sanitary waste waters leads to substantial process improvements. In particular, the rate of reaction can be improved by several fold by establishing the proper environmental conditions for microbial growth in a fermentation system. Recent work on the concentric cylinder air lift has shown it to be an economical fermentor with many advantages over conventional fermentors. An attempt to improve the economical performance of this system led to the development of the thin channel rectangular air lift fermentor. This was based upon a theoretical analysis of performance parameters. The analysis indicates decreased bubble coalescence, increased bubble entrainment, decreased power costs, increased mass transfer coefficients, and decrease capital costs. Experience using a prototype thin channel rectangular air lift system with sanitary and industrial waste-water treatment systems has demonstrated exceptionally high rates of BOD removal at low operating and capital costs.     

Development of a simple particle bombardment device for gene transfer into plant cells

A simple particle bombardment device was designed, constructed and shown to be efficient for the delivery of DNA into plant cells. High levels of transient -glucuronidase expression were observed in alfalfa suspension-cultured cells and embryogenic soybean suspension-cultured cells. Expression of -glucuronidase in alfalfa suspension-cultured cells was used to optimize the bombardment conditions for the device. Transient gene expression in alfalfa was found to be dependent on the state of the target tissue, the size of particles employed, the helium pressure used to accelerate the particles and the distance travel led by the tungsten particles carrying DNA.Abbreviations 2,4-d 2,4-dichlorophenoxyacetic acid - GUS -glucuronidase - MS Murashige & Skoog (1962) medium     

Ultrasound: mechanical gene transfer into plant cells by sonoporation

Development of nonviral gene transfer methods would be a valuable alternative of gene therapy or transformation. Ultrasound can produce a variety of nonthermal bioeffects via acoustic cavitation. Cavitation bubbles can induce cell death or transient membrane permeabilization (sonoporation) on cells. Application of sonoporation for gene transfer into cells or tissues develops quickly in recent years. Many studies have been performed in vitro exposure systems to a variety of cell lines transfected successfully. In vivo, cavitation initiation and control are more difficult, but can be enhanced by ultrasound contrast agents (microbubbles). The use of ultrasound for nonviral gene delivery has been applied for mammalian systems, which provides a fundamental basis and strong promise for development of new gene therapy methods for clinical medicine. In this paper, ultrasound applied to plant cell transformation or gene transfer is reviewed. Recently, most researches are focused on sonication-assisted Agrobacterium-mediated transformation (SAAT) in plant cells or tissues. Microbubbles are also proposed to apply to gene transfer in plant cells and tissues.     

Oxygen transfer in broths of plant cells at high density

The rheological properties of the culture broths of some plant cells (Cudrania tricuspidata, Vinca rosea, and Agrostemma githago) at high density (10-18 g dry wt/L) were measured, and oxygen transfer in the broths in various bioreactors was investigated. The rheological properties of the broths were dependent on the size, specific gravity, and concentration of the cell aggregates contained in the broths. The broths were non-Newtonian and pseudoplastic fluids. The flow behavior index n was fairly constant (0.53) and the consistency index K varied in proportion to the sixth-to-seventh power of the cell mass concentration M. The apparent viscosity mu(a) of the broths was in proportion to the 6.5th power of M. The oxygen transfer in the broths was discussed on the basis of the results obtained for suspensions of granulated agars (agar concentration, 5.8%) in water, which were similar to the broths in rheological properties. The volumetric oxygen transfer coefficient k(L)a in the broths was dependent on mu(a)(k(L)a proportional, variant mu(a) (-m)) and decreased greatly at a certain apparent viscosity, mu(ac). The values of m and mu(ac) were closely related to the aeration-agitation mechanisms of the bioreactors. The values of mu(ac) in aeration-agitation type bioreactors was larger than that in aeration-type bioreactors, whereas for m, the reverse was true.     

The lip lift

Attention is brought to a seldom-considered sign of aging--the lengthening of the upper lip. It is easily corrected by excising a wavy ellipse of lip skin and hiding the scar up under the nose. A vertical midline component may be added. The scars are minimal, and the results have been excellent in 83 patients.