Bioreactor mixing efficiency modulates the activity of a prpoS::GFP reporter gene in E. coli

<p>Abstract</p> <p>Background</p> <p>Extensive studies have shown that up-scaling of bioprocesses has a significant impact on the physiology of the microorganisms. Among the factors associated with the fluid dynamics of the bioreactor, concentration gradients induced by loss of the global mixing efficiency associated with the increasing scale is the main phenomena leading to strong physiological modifications at the level of the microbial population. These changes are not fully understood since they involve complex physiological mechanisms. In this work, we intend to investigate, at the single cell level, the expression of the rpoS gene associated with the stress response of <it>E. coli</it>. The cultures of the reporter strain have been performed in a small scale reactor as well as in a series of scaled-down bioreactors able to induce extracellular perturbations with increasing level of magnitude.</p> <p>Results</p> <p>The rpoS level has been monitored by the aim of a transcriptional reporter gene based on the synthesis of the green fluorescent protein (GFP). It has been observed that the level of GFP increases during the transition from batch to fed-batch phase. After this initial increase, the GFP content of the cell drops, primarily due to the dilution by cell division. However, a significant drop of the GFP content has been observed if using a partitioned bioreactor, for which the mixing conditions are very bad, leading to the exposure of the cells to cyclic and stochastic extracellular fluctuations. If considering the flow cytometric profile of the cell to cell GFP content, this drop has to be attributed to the appearance of segregation at the level of the GFP content among the microbial population.</p> <p>Conclusion</p> <p>The generation of extracellular perturbations (in the present case, at the level of the sugar concentration and the dissolved oxygen level) has led to a drop at the level of the rpoS expression level. This drop has to be attributed to a segregation phenomenon in microbial population, with a major sub-population exhibiting a low expression level and a minor sub-population keeping its initial elevated expression level. The intensity of the segregation, as well as its time of appearance during the culture can be related to the bioreactor mixing efficiency.</p

La Belgique en toutes lettres

QUAGHEBEUR, Marc. La Belgique en toutes lettres. Textes assemblés par Véronique Jago-Antoine et Hugues Robaye. Bruxelles: Luc Pire, coll. « Espace Nord », 2008. Vol. I: Le pays (288 p.) ISBN: 978-2-50700-156-8; Vol. II: L´Histoire et les hommes (464 p.) ISBN: 978- 2-50700-157-5; Vol. III : Tranches de vie (304 p.) ISBN : 978-2-50700-158-2

Les littératures contemporaines sous l´angle du concept de nation - DOI: 10.4025/actascilangcult.v31i1.998

Devant l´actuelle déstabilisation du concept de nation en contexte de mondialisation, quelles sont la pertinence et l´actualité d´une étude des littératures contemporaines sous l´angle de la nation ? Faut-il constater l´obsolescence du concept de littérature nationale ? Pour sortir d´une impasse théorique, la perspective historique s´avère indispensable et une étude des avatars de la nation, concept et réalité, met sur la voie d´une vision élargie où la nation est révélée comme représentation: fiction symbolique ou mythe. À côté d´un modèle mythique hégémonique privilégiant l´homogène, un autre modèle national est identifié, caractérisé par l´hétérogène et servant d´auxiliaire aux collectivités ex-centriques en quête d´une identification. Comme expression privilégiée du mythe de la nation, la littérature joue un rôle fondamental dans l´invention de représentations nationales inédites, ce qui justifie la pérennité d´une recherche (sociologique et/ou thématique) centrée sur le littéraire contemporain (ou passé, pourvu qu´elle opère à partir d´un point de vue actualisé) envisagé sous l´angle de la nation.Diante da atual desestabilização do conceito de nação em contexto de globalização, quais são a pertinência e a atualidade de um estudo das literaturas contemporâneas sob o ângulo da nação? Haverá de se constatar a obsolescência do conceito de literatura nacional? Para sair de um impasse teórico, apresenta-se uma história do conceito de nação, desde suas origens no século XVIII até os dias de hoje. Abre-se caminho para uma visão ampliada da nação, ou seja, para uma definição que a revela como representação: ficção simbólica ou mito. Ao lado de um modelo mítico hegemônico que privilegia o homogêneo, um outro modelo nacional é identificado, caracterizado pelo heterogêneo e auxiliando coletividades ex-cêntricas no seu esforço de identificação. Sendo uma expressão privilegiada do mito da nação, a literatura tem um papel na invenção de representações nacionais inéditas, o que justifica a perenidade de uma pesquisa (sociológica e/ou temática) do literário contemporâneo – ou passado, por tanto que seja a partir de uma visão atualizada - no âmbito da nação