VIII Encuentro de Docentes e Investigadores en Historia del Diseño, la Arquitectura y la Ciudad

Acta de congresoLa conmemoración de los cien años de la Reforma Universitaria de 1918 se presentó como una ocasión propicia para debatir el rol de la historia, la teoría y la crítica en la formación y en la práctica profesional de diseñadores, arquitectos y urbanistas. En ese marco el VIII Encuentro de Docentes e Investigadores en Historia del Diseño, la Arquitectura y la Ciudad constituyó un espacio de intercambio y reflexión cuya realización ha sido posible gracias a la colaboración entre Facultades de Arquitectura, Urbanismo y Diseño de la Universidad Nacional y la Facultad de Arquitectura de la Universidad Católica de Córdoba, contando además con la activa participación de mayoría de las Facultades, Centros e Institutos de Historia de la Arquitectura del país y la región. Orientado en su convocatoria tanto a docentes como a estudiantes de Arquitectura y Diseño Industrial de todos los niveles de la FAUD-UNC promovió el debate de ideas a partir de experiencias concretas en instancias tales como mesas temáticas de carácter interdisciplinario, que adoptaron la modalidad de presentación de ponencias, entre otras actividades. En el ámbito de VIII Encuentro, desarrollado en la sede Ciudad Universitaria de Córdoba, se desplegaron numerosas posiciones sobre la enseñanza, la investigación y la formación en historia, teoría y crítica del diseño, la arquitectura y la ciudad; sumándose el aporte realizado a través de sus respectivas conferencias de Ana Clarisa Agüero, Bibiana Cicutti, Fernando Aliata y Alberto Petrina. El conjunto de ponencias que se publican en este Repositorio de la UNC son el resultado de dos intensas jornadas de exposiciones, cuyos contenidos han posibilitado actualizar viejos dilemas y promover nuevos debates. El evento recibió el apoyo de las autoridades de la FAUD-UNC, en especial de la Secretaría de Investigación y de la Biblioteca de nuestra casa, como así también de la Facultad de Arquitectura de la UCC; va para todos ellos un especial agradecimiento

The alternative role of enterobactin as an oxidative stress protector allows Escherichia coli colony development.

Numerous bacteria have evolved different iron uptake systems with the ability to make use of their own and heterologous siderophores. However, there is growing evidence attributing alternative roles for siderophores that might explain the potential adaptive advantages of microorganisms having multiple siderophore systems. In this work, we show the requirement of the siderophore enterobactin for Escherichia coli colony development in minimal media. We observed that a strain impaired in enterobactin production (entE mutant) was unable to form colonies on M9 agar medium meanwhile its growth was normal on LB agar medium. Given that, neither iron nor citrate supplementation restored colony growth, the role of enterobactin as an iron uptake-facilitator would not explain its requirement for colony development. The absence of colony development was reverted either by addition of enterobactin, the reducing agent ascorbic acid or by incubating in anaerobic culture conditions with no additives. Then, we associated the enterobactin requirement for colony development with its ability to reduce oxidative stress, which we found to be higher in media where the colony development was impaired (M9) compared with media where the strain was able to form colonies (LB). Since oxyR and soxS mutants (two major stress response regulators) formed colonies in M9 agar medium, we hypothesize that enterobactin could be an important piece in the oxidative stress response repertoire, particularly required in the context of colony formation. In addition, we show that enterobactin has to be hydrolyzed after reaching the cell cytoplasm in order to enable colony development. By favoring iron release, hydrolysis of the enterobactin-iron complex, not only would assure covering iron needs, but would also provide the cell with a molecule with exposed hydroxyl groups (hydrolyzed enterobactin). This molecule would be able to scavenge radicals and therefore reduce oxidative stress

List of strains and plasmids used in this work.

<p>List of strains and plasmids used in this work.</p

Effect of oxidative stress on <i>entE</i> expression.

<p>Panel A shows the effect of 1mM hydrogen peroxide (H₂O₂) or 100 μM paraquat (PQ) on <i>entE</i> expression. Panel B and C display the effect of the same stressors in the presence of 5 mM ascorbic acid (ASC) and 100 μM FeCl₃, respectively. For A, B and C, a control without addition of H₂O₂ or PQ was included. <i>entE</i> expression was determined by means of a β-galactosidase assay as described in the Material and Methods section. Values are means ±SD for three independent experiments.</p

Effect of H₂O₂ and paraquat on iron availability.

<p>The activity of the Fur-regulated promoter <i>ryhB</i> was used as an indicator of intracellular iron levels. The expression of <i>ryhB</i> was estimated by β-galactosidase activity in an <i>entE</i> mutant transformed with the plasmid pALM23 that carries the <i>ryhB</i>-<i>lacZ</i> fusion. Panel A shows that addition of 1 mM H₂O₂ did not affect the activity of the promoter meanwhile 100 μM paraquat addition only slightly increased it. Panel B shows that the promoter activity is equally affected by iron addition (100 μM FeCl₃) even in the presence of 1 mM H₂O₂ or 100 μM paraquat. Values are means ±SD for three independent experiments.</p

Growth of <i>E. coli</i> wild-type (wt) and <i>entE</i> strains in liquid and solid media.

<p>A) Liquid aerated minimal M9 medium cultures of wild-type strain (blue squares), <i>entE</i> strain (green circles) and <i>entE</i> strain in the same media but supplemented with 100 µM FeCl₃ (red triangles). Growth (OD₆₀₀) was determined at the indicated times. B) Lawn growth of wt and <i>entE E. coli</i> strains on M9A. A stationary phase culture of <i>entE E. coli</i> strain was serially diluted (10⁻¹ to 10⁻⁴) and an aliquot of these dilutions was applied on M9A or M9A supplemented with 100 µM FeCl₃. As control, the same dilutions of a wt strain overnight culture were applied on M9A medium. Lawn growth was compared at 8 hours of incubation. C) Colony growth of wt and <i>entE E. coli</i> on LBA. A stationary phase culture of <i>entE E. coli</i> strain was serially diluted and an aliquot of dilutions 10⁻⁶ to 10⁻⁸ were applied on LBA or LBA supplemented with 100 µM FeCl₃. As control, the same dilutions of an overnight culture of the wt strain were applied on LBA medium. After overnight incubation, colonies sizes were compared. D) Activity of the <i>rhyB</i> promoter estimated by β-galactosidase activity as an indirect measure of the intracellular iron content (The higher the promoter expression, the lower the iron content <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0084734#pone.0084734-Ma2" target="_blank">[48]</a>). Both wild-type strain and <i>entE</i> mutant respond to iron addition. The plasmid pALM23 carries the <i>ryhB- lacZ</i> fusion.</p

Effect of H₂O₂ and iron supplementation on catechol production.

<p>Quantitation of catechol levels produced by wild-type <i>E</i>. <i>coli</i> was done using Arnow assay on enterobactin-enriched extracts. Extracts were obtained from cultures grown in M9 medium supplemented with 1 mM H₂O₂, 25 μM FeCl₃ or both. Results are expressed as μM equivalents by comparison to a standard curve prepared using DHBA. Values are means ±SD for three independent experiments.</p

Absence of <i>entE</i> expression induction by oxidative stress in a <i>soxS</i> mutant.

<p>The expression of <i>entE</i> was estimated by β-galactosidase activity in a <i>ΔentE</i>::<i>lacZ</i> Δ<i>soxS</i> mutant as described in the Material and Methods section. In the absence of the global transcriptional regulator SoxS, H₂O₂ and paraquat do not induce <i>entE</i> expression. The repressive effect of iron (100 μM FeCl₃) is preserved. Values are means ±SD for three independent experiments.</p

List of strains and plasmids used in this work.

a<p>CGSC, <i>Escherichia coli</i> Genetic Stock Center;</p

A) Type of growth of <i>E. coli fepD</i> and <i>fepG</i> mutants streaked in M9A and incubated overnight in aerobic conditions. B) Levels of reactive oxygen species in <i>E. coli</i> wild-type and <i>fepD</i>, <i>fepG, entS</i> and <i>entE</i> mutants grown in M9 medium. Quantitation of ROS levels was done using the DCFA-DA probe. Fluorescence intensities are relative to that of the control. Control: wt grown in M9 medium. Error bars = SD, n = 3.

<p>A) Type of growth of <i>E. coli fepD</i> and <i>fepG</i> mutants streaked in M9A and incubated overnight in aerobic conditions. B) Levels of reactive oxygen species in <i>E. coli</i> wild-type and <i>fepD</i>, <i>fepG, entS</i> and <i>entE</i> mutants grown in M9 medium. Quantitation of ROS levels was done using the DCFA-DA probe. Fluorescence intensities are relative to that of the control. Control: wt grown in M9 medium. Error bars = SD, n = 3.</p