Smaller Gene Networks Permit Longer Persistence in Fast-Changing Environments

The environments in which organisms live and reproduce are rarely static, and as the environment changes, populations must evolve so that phenotypes match the challenges presented. The quantitative traits that map to environmental variables are underlain by hundreds or thousands of interacting genes whose allele frequencies and epistatic relationships must change appropriately for adaptation to occur. Extending an earlier model in which individuals possess an ecologically-critical trait encoded by gene networks of 16 to 256 genes and random or scale-free topology, I test the hypothesis that smaller, scale-free networks permit longer persistence times in a constantly-changing environment. Genetic architecture interacting with the rate of environmental change accounts for 78% of the variance in trait heritability and 66% of the variance in population persistence times. When the rate of environmental change is high, the relationship between network size and heritability is apparent, with smaller and scale-free networks conferring a distinct advantage for persistence time. However, when the rate of environmental change is very slow, the relationship between network size and heritability disappears and populations persist the duration of the simulations, without regard to genetic architecture. These results provide a link between genes and population dynamics that may be tested as the -omics and bioinformatics fields mature, and as we are able to determine the genetic basis of ecologically-relevant quantitative traits

Development of Scientific Competences in Chemistry Courses

Enseñar química en los primeros años de educación universitaria es clave en la formación de futuros profesionales, puesto que, además de proveer los conocimientos que aportan las ciencias básicas, contribuye al desarrollo de competencias científicas para que el estudiante resuelva problemas reales, a partir de la búsqueda adecuada de información en fuentes confiables y su lectura, con el propósito de desarrollar habilidades analíticas, críticas y creativas. Es por esto que, como estrategia de innovación pedagógica, el Departamento de Ciencias Básicas de la Universidad de La Salle ha venido implementando desde el año 2016 la formulación de un proyecto de investigación en los cursos de química. En el marco de esta estrategia, desde el II-2018 las autoras se abocaron a la reflexión e implementación de la estrategia didáctica que propende por el desarrollo de competencias científicas en los cursos de Química General, Química Orgánica y Bioquímica desde tareas, investigación y aprendizaje de problemáticas vigentes en Colombia y en el mundo.Abstract: Teaching chemistry in the first years of university education is key in the training of future professionals since, in addition to providing the knowledge of the basic sciences, it contributes to the development of scientific skills that lead to the student to solve real problems, starting from the appropriate search of information in reliable sources and its reading with the purpose of developing analytical, critical and creative skills. Therefore, as a pedagogical innovation strategy, the formulation of a research project in chemistry courses has been implemented since 2016 by the Department of Basic Sciences of the Universidad de La Salle. Within the framework of this strategy, from II-2018 the authors focused on the reflection and implementation of the didactic strategy that depends on the development of scientific competences in the courses of General Chemistry, Organic Chemistry and Biochemistry from tasks, research and learning of current problems in Colombia or in the world

Determination of the intracellular pH (pHi) of growing cells of Saccharomyces cerevisiae : the effect of reduced-expression of the membrane H+-ATPase

This report describes the use of the fluorescent probe, 5(6)-carboxyfluorescein diacetate succinimidyl ester (CFDA-SE), to determine pH(i) in growing cells of the spoilage yeast Saccharomyces cerevisiae. The technique is based on the pH-dependent intracellular fluorescence of the probe in the cytosol of the cell. The major advantage of this probe over other derivatives is the presence of a succinimidyl group which binds to aliphatic amines in cellular proteins. This allows for the determination of pH, under conditions that either permeabilise the cell membrane, or increase active extrusion, and would otherwise result in loss of the intracellular probe to the external medium. Optimal loading of the probe into cells only occurred after exposure to a mild stress regime of 37 degrees C for 24 h in 100 mM citric/phosphate buffer, pH 4.0. This loading regime was selected because there was no appreciable effect on cell viability or subsequent growth rate in batch culture under optimal conditions. The pH(i) of yeast cells was measured after incubation in citric/phosphate buffer and gave values comparable to those measured by other techniques in the literature. Also, we were able to detect rapid changes in pH(i) induced by the addition of a known disrupter of pH(i) homeostasis in yeast, the weak-acid food preservative, sorbic acid. Finally, successful determination of pH(i) was made in growing cells of an isogenic parent (PMA I) and a mutant with reduced-expression of the membrane H+-ATPase, pma1-205. As might be expected, the pH(i) in the mutant strain was reduced compared to the parent. Comparison of growth and pH, in growing cells of either strain revealed no correlation between pH, and exit from lag phase. These results are discussed in relation to previous findings. (C) 1998 Elsevier Science B.V.</p

Inhibitory action of a truncated derivative of the amphibian skin peptide Dermaseptin s3 on Saccharomyces cerevisae

The inhibitory activity of a truncated derivative of the natural amphibian skin peptide dermaseptin s3-(1-16)-NH2 [DS s3 (1-16)] against Saccharomyces cerevisiae was studied. Significant growth inhibition was observed after exposure to 3.45 mu g of the peptide per mi at pH 6.0 and 7.0, with complete growth inhibition occurring at 8.63 mu g of peptide per mi for all pH values tested. Using confocal scanning laser microscopy, we have shown that DS s3 (1-16) disrupted the yeast cell membrane resulting in the gross permeabilization of the cell to the nuclear stain ethidium bromide, However, the principal inhibitory action of the peptide was not due to disruption of intracellular pH homeostasis. Instead, growth inhibition by the peptide correlated with the efflux of important cellular constituents such as ADP, ATP, RNA, and DNA into the surrounding medium. The combination of DS s3 (1-16) with mild heating temperatures as low: as 35 degrees C significantly enhanced the inhibitory effect of the peptide (8.63 mu g/ml), and at 45 degrees C greater than 99% of the population was killed in 10 min. In summary, a derivative of a natural antimicrobial peptide has potential, either alone or in combination with mild heating, to prevent the growth of or kill spoilage yeast.</p