Analysis of the effects of hyperbaric gases on S. cerevisiae cell cycle through a morphological approach

The effects of hyperbaric gases on the cell cycle of Saccharomyces cerevisiae were studied in batch cultures under pressures between 0.1 and 0.6 MPa and different gas compositions (air, oxygen, nitrogen or carbon dioxide). Classification of S. cerevisiae cells based on their morphology stages was obtained using an automatic image analysis procedure. Information on the distribution of different sub-populations along the cell cycle is reported. A structured morphological model was developed and used to describe the measured data. The results herein reported demonstrate that the bud separation phase is the limiting step in cell duplication. Additionally, the influence of the environmental conditions, specially the oxygen partial pressure, on the START event is reported. Under anaerobic conditions, no significant influence of hyperbaric gases on the cell cycle was verified.CAPES/GRICES, CNPq (Brazil) Fundação para a Ciência e a Tecnologia (FCT

Saccharomyces cerevisiae morphology under hyperbaric gases

The effects of hyperbaric stress on the morphology of Saccharomyces cerevisiae were studied in batch cultures under pressures between 0.1 MPa and 0.6 MPa and different gas compositions (air, O2, N2, or CO2), covering aerobic and anaerobic conditions. A method using automatic image analysis for cell classification based on their morphology was applied to experimental data. Cell viability was assessed through the Methylene Blue staining method and the percentages of viable and non-viable cells were also estimated using digital image processing. The results show that the effect of pressure on cell activity strongly depends on the nature of the gas used for pressurization. While nitrogen and air to a maximum of 0.6 MPa of pressure were innocuous to yeast, oxygen and carbon dioxide pressure caused cell inactivation, which was confirmed by the reduction on the number of budding cells with time and also a decrease in the average cell size (0.6 MPa CO2). A model taking into account cell viability reveals the opposing effects between oxygen availability and the baric and oxidative stresses present on the system. It is shown that cell viability in general is not constant during the experiments but strongly depends on the environment

Classification of Saccharomyces cerevisiae morphology employing image analysis

Population dynamics of microbial systems can be described by several approaches and in various levels of complexity, each of them arising from specific goals and limitations. From the process-engineering viewpoint there is a need for a comprehensive mathematical model describing population dynamics in terms of measurable entities (microbes) and chemicals involved (limiting substrate, dissolved oxygen, etc.), as well as process configuration (number and type of reactors, interconnections, etc.) and process parameters (inlet flow rate and composition, reactor holdup, and more) [1]. The description of intricate population dynamics and the inference of cell states lead to complex models with a great number of parameters. Knowledge about whole cell cycle and morphology classification is imperative, since a considerable difference exists between the cell description employed in model formulation and the laboratory reality. As soon as in biological systems exists a relationship between cell morphology and productivity, some authors drive efforts towards the on-line measurement of biomass component to avoid process delays [2],[4] or to determine cellular characteristics related to its morphology and/or physiology through image processing analysis [5],[6],[7]. Saccharomyces cerevisiae size and shape distribution are affected by growth rate, mutation, and environmental conditions (composition, temperature, pressure, presence of oxidant agents, etc.). Although its shape usually assumes an ellipsoid contour it is modified along the cell cycle by bud formation and growing attached to the mother [5]. This work deals with S. cerevisiae classification based on morphology analysis. Image acquisition was conducted in an optical microscope (x 400 magnification) coupled with a black and white camera and linked to a microcomputer by a frame grabber. Traditional tools generally used for image enhancing were employed. Feature extraction and objects separation were necessary to classify "mothers" and "daughters" and to determine its frequency in the analyzed samples. Cells were automatically divided in five different classes with respect to bud size compared to the respective mother through image analysis employing Matlab (v.6.1, The Mathworks Inc.). This methodology was validated with distinct samples and employed along Sacharomyces cerevisiae growth in different operational conditions. The data herein obtained is being used for morphological structured model formulation.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); CAPES

Diffusive conductors as Andreev interferometers

We present a novel mechanism of phase-dependent electric transport in diffusive normal metal-superconductor structures. We provide a detailed theoretical and numerical analysis of recent unexplained experiments essentially explaining them.Comment: Self extracting file, 7 pages latex and 4 postscript figures. The paper is also available at http://www.tn.tudelft.nl/tn/thspap.html In this revision we resolved some printing problems concerning figures 2 and

On compatibility of string effective action with an accelerating universe

In this paper, we fully investigate the cosmological effects of the moduli dependent one-loop corrections to the gravitational couplings of the string effective action to explain the cosmic acceleration problem in early (and/or late) universe. These corrections comprise a Gauss-Bonnet (GB) invariant multiplied by universal non-trivial functions of the common modulus $\sigma$ and the dilaton $\phi$. The model exhibits several features of cosmological interest, including the transition between deceleration and acceleration phases. By considering some phenomenologically motivated ansatzs for one of the scalars and/or the scale factor (of the universe), we also construct a number of interesting inflationary potentials. In all examples under consideration, we find that the model leads only to a standard inflation ($w \geq -1$) when the numerical coefficient $\delta$ associated with modulus-GB coupling is positive, while the model can lead also to a non-standard inflation ($w<-1$), if $\delta$ is negative. In the absence of (or trivial) coupling between the GB term and the scalars, there is no crossing between the $w -1$ phases, while this is possible with non-trivial GB couplings, even for constant dilaton phase of the standard picture. Within our model, after a sufficient amount of e-folds of expansion, the rolling of both fields $\phi$ and $\sigma$ can be small. In turn, any possible violation of equivalence principle or deviations from the standard general relativity may be small enough to easily satisfy all astrophysical and cosmological constraints.Comment: 30 pages, 8 figures; v2 significant changes in notations, appendix and refs added; v3 significant revisions, refs added; v4 appendix extended, new refs, published versio

Comparative root transcriptome of wild Arachis reveals NBS-LRR genes related to nematode resistance.

Na publicação: Soraya C. M. Leal-Bertioli; Ana Claudia Guerra Araujo e Patricia Messenberg Guimaraes

Neutron-Proton Differential Flow as a Probe of Isospin-Dependence of Nuclear Equation of State

The neutron-proton differential flow is shown to be a very useful probe of the isospin-dependence of the nuclear equation of state (EOS). This novel approach utilizes constructively both the isospin fractionation and the nuclear collective flow as well as their sensitivities to the isospin-dependence of the nuclear EOS. It also avoids effectively uncertainties associated with other dynamical ingredients of heavy-ion reactions at intermediate energies.Comment: 10 pages + 3 figures. Phys. Rev. Lett. (2000) in pres

Chameleon field and the late time acceleration of the universe

In the present work, it is shown that a chameleon scalar field having a nonminimal coupling with dark matter can give rise to a smooth transition from a decelerated to an accelerated phase of expansion for the universe. It is surprising to note that the coupling with the chameleon scalar field hardly affects the evolution of the dark matter sector, which still redshifts as $a^{-3}$.Comment: 7 pages, 2 figure