Control of electroporation efficiency by measuring the conductivity of the tissues

The method for measuring the efficiency of the electroporation process for living tissue is offered. The method consists in measuring the conductivity of tissue before and after the electroporation process. The measurements confirmed the efficiency of the method

Expression of the Sinorhizobium meliloti C4-dicarboxylate transport gene during symbiosis with the Medicago host plant

During symbiosis between Sinorhizobium meliloti and the Medicago host plant, the energy required to fix atmospheric nitrogen, is derived from the plant photosynthate. Current evidence indicates that C 4 -dicarboxylates (dCA) are the major and probably only source of carbon provided to the bacteroids in sufficiently high amounts to support symbiotic N 2 -fixation. The ability of the microsymbiont to take up dCA is essential for the establishment of an effective symbiosis. The dct A gene codes for a high affinity dCA permease (DctA). The regulatory dct BD genes code for a two-component regulatory system. Under free-living conditions, the regulatory dct BD genes are essential for activation of the dct A promoter. Bacteroids isolated from nodules induced by regulatory dct BD mutants take up dCA efficiently. This demonstrated that in the specific environment of the nodule, regulatory molecules other than DctBD, are involved in the expression of the dct A promoter.The aim of this work was to study the regulation of the dct A gene during symbiosis of S.meliloti with the Medicago host plants and in particular to characterise this alternative mechanism of symbiotic activation (ASA). Using gene fusions of the dct A expression signals to the lac Z reporter gene, in combination with histochemical staining of plant tissue, the regulation of the S.melilotidct A gene was studied in situ during the symbiosis with the Medicago host plants. The major findings of this work are the following.1) The ASA mechanism is only active at the late stages of the symbiosis.First, it is established that in a wild-type background, the dct A gene is expressed during the early and late stages of symbiosis (A). In contrast in nodules induced by a regulatory dct B or dct D mutant, a distinct late symbiotic pattern of dct A expression was observed (B). This meant that the ASA is an exclusive late symbiotic mechanism. The temporal and spatial pattern of DctBD-independent dct A expression in nodules induced on the alfalfa host plant was always very similar to that of the nif H gene fusion. This late symbiotic manifestation of the ASA means that the early expression of dct A observed in wild-type nodules is necessarily DctBD dependent.2) The ASA requires sequences downstream of the dct A promoter for activity.We also found that certain gene fusions lacking the extreme N-terminal domain of the dct A coding region did not respond to the ASA. This was remarkable since these gene fusions appeared to be correctly regulated by the DctBD system under free-living conditions. In contrast, gene fusions containing the first 8 amino-acids of the dct A coding region were efficiently activated by the ASA (B). We concluded that some cis-acting nucleotide sequences, located immediately downstream of the dct A promoter in the beginning of the coding region, are required for ASA activity3) The UAS sites of the dct A promoter are not essential for ASA activity.During symbiosis dct A:: lac Z gene fusions lacking the upstream activator sites (UAS) were expressed in wild-type nodules (D) and at a similar level in a dct D mutant background (E). The pattern of temporal and spatial expression in a wild-type nodule (D) was similar to that observed for DctBD independent activation of other gene fusions containing the UAS (B). We concluded that the UAS, which are indispensable for the activation by the DctBD system, are not essential for the activation of the dct A promoter by the ASA.4) The alternative symbiotic activator requires NifA.We observed gene fusions lacking the UAS sequences are efficiently expressed in the wild-type and dct D mutant backgrounds (D;E), but were not activated in nodules formed by a nif A mutant strain (F).Working with the Medicago truncatula host plant, we found that in nodules induced by a dct D mutant strain, the dct A gene was not expressed efficiently. We also observed that the nif A gene is expressed in these nodules at a level, which is strongly reduced in comparison to the level of nif A expression in nodules induced on M.sativa . We concluded that an efficient expression of the nif A gene is required for ASA activity.5) The ASA is not essential for symbiotic N 2 -fixation.Monitoring dct A activity with the dct A:: lac Z gene fusions which are not activated by the ASA, demonstrated that the DctBD system alone is sufficient to express the dct A promoter during symbiosis. Additionally we observed that although the ASA does not function in nodules induced on the Medicago truncatula host plant, these nodules were efficient for symbiotic N 2 -fixation. This indicates that activation of the dct A promoter by the ASA is not required for symbiotic N 2 -fixation.</p

Static Properties of Trapped Bose-Fermi Mixed Condensate of Alkali Atoms

Static properties of a bose-fermi mixture of trapped potassium atoms are studied in terms of coupled Gross-Pitaevskii and Thomas-Fermi equations for both repulsive and attractive bose-fermi interatomic potentials. Qualitative estimates are given for solutions of the coupled equations, and the parameter regions are obtained analytically for the boson-density profile change and for the boson/fermion phase separation. Especially, the parameter ratio $R_{int}$ is found that discriminates the region of the large boson-profile change. These estimates are applied for numerical results for the potassium atoms and checked their consistency. It is suggested that a small fraction of fermions could be trapped without an external potential for the system with an attractive boson-fermion interaction.Comment: 8 pages,5 figure

Quantum degeneracy and interaction effects in spin-polarized Fermi-Bose mixtures

Various features of spin-polarized Fermi gases confined in harmonic traps are discussed, taking into account possible perspectives of experimental measurements. The mechanism of the expansion of the gas is explicitly investigated and compared with the one of an interacting Bose gas. The role of interactions on the equilibrium and non equilibrium behaviour of the fermionic component in Fermi-Bose mixtures is discussed. Special emphasis is given to the case of potassium isotopes mixtures.Comment: 5 pages, 3 figures, revtex, to be published in J. Phys.

A white-light trap for Bose-Einstein condensates

We propose a novel method for trapping Bose-condensed atoms using a white-light interference fringe. Confinement frequencies of tens of kHz can be achieved in conjunction with trap depths of only a few micro-K. We estimate that lifetimes on the order of 10 s can be achieved for small numbers of atoms. The tight confinement and shallow depth permit tunneling processes to be used for studying interaction effects and for applications in quantum information.Comment: 10 pages with 3 figure

Creating massive entanglement of Bose condensed atoms

We propose a direct, coherent coupling scheme that can create massively entangled states of Bose-Einstein condensed atoms. Our idea is based on an effective interaction between two atoms from coherent Raman processes through a (two atom) molecular intermediate state. We compare our scheme with other recent proposals for generation of massive entanglement of Bose condensed atoms.Comment: 5 pages, 3 figures; Updated figure 3(a), original was "noisy

Quantum and Semiclassical Calculations of Cold Atom Collisions in Light Fields

We derive and apply an optical Bloch equation (OBE) model for describing collisions of ground and excited laser cooled alkali atoms in the presence of near-resonant light. Typically these collisions lead to loss of atoms from traps. We compare the results obtained with a quantum mechanical complex potential treatment, semiclassical Landau-Zener models with decay, and a quantum time-dependent Monte-Carlo wave packet (MCWP) calculation. We formulate the OBE method in both adiabatic and diabatic representations. We calculate the laser intensity dependence of collision probabilities and find that the adiabatic OBE results agree quantitatively with those of the MCWP calculation, and qualitatively with the semiclassical Landau-Zener model with delayed decay, but that the complex potential method or the traditional Landau-Zener model fail in the saturation limit.Comment: 21 pages, RevTex, 7 eps figures embedded using psfig, see also http://www.physics.helsinki.fi/~kasuomin

The density dependence of the transition temperature in a homogenous Bose flui

Transition temperature data obtained as a function of particle density in the $^4$He-Vycor system are compared with recent theoretical calculations for 3D Bose condensed systems. In the low density dilute Bose gas regime we find, in agreement with theory, a positive shift in the transition temperature of the form $\Delta T/T_0 = \gamma(na^{3})^{1/3}$. At higher densities a maximum is found in the ratio of $T_c /T_0$ for a value of the interaction parameter, na$^3$, that is in agreement with path-integral Monte Carlo calculations.Comment: 4 pages, 3 figure

Formation of Giant Quasibound Cold Diatoms by Strong Atom-Cavity Coupling

We show that giant quasi-bound diatomic complexes, whose size is typically hundreds of nm, can be formed by intra-cavity cold diatom photoassociation or photodissociation in the strong atom-cavity coupling regime.Comment: 4 pages, 3 figure

Application of Enzymes in Industrial Organic Synthesis

Aminopeptidase- and amidase-based methods for the production of enantiomerically pure amino acids, intermediates for pharmaceuticals and agrochemicals, are discussed. Furthermore, enzymatic syntheses of the dipeptide sweetener aspartame and semisynthetic antibiotics (such as ampicillin, amoxicillin, cephalexin, and cefadroxil) are highlighted