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

Reduced levels of reactive oxygen species correlate with inhibition of apoptosis, rise in thioredoxin expression and increased bovine leukemia virus proviral loads

BACKGROUND: Bovine Leukemia virus (BLV) is a deltaretrovirus that induces lymphoproliferation and leukemia in ruminants. In ex vivo cultures of B lymphocytes isolated from BLV-infected sheep show that spontaneous apoptosis is reduced. Here, we investigated the involvement of reactive oxygen species (ROS) in this process. RESULTS: We demonstrate that (i) the levels of ROS and a major product of oxidative stress (8-OHdG) are reduced, while the thioredoxin antioxidant protein is highly expressed in BLV-infected B lymphocytes, (ii) induction of ROS by valproate (VPA) is pro-apoptotic, (iii) inversely, the scavenging of ROS with N-acetylcysteine inhibits apoptosis, and finally (iv) the levels of ROS inversely correlate with the proviral loads. CONCLUSION: Together, these observations underline the importance of ROS in the mechanisms of inhibition of apoptosis linked to BLV infection

The HTLV-1 Tax interactome

The Tax1 oncoprotein encoded by Human T-lymphotropic virus type I is a major determinant of viral persistence and pathogenesis. Tax1 affects a wide variety of cellular signalling pathways leading to transcriptional activation, proliferation and ultimately transformation. To carry out these functions, Tax1 interacts with and modulates activity of a number of cellular proteins. In this review, we summarize the present knowledge of the Tax1 interactome and propose a rationale for the broad range of cellular proteins identified so far

Interaction of HTLV-1 Tax with minichromosome maintenance proteins accelerates the replication timing program

The Tax oncoprotein encoded by the Human T-cell leukemia virus type 1 (HTLV-1) plays a pivotal role in viral persistence and pathogenesis. HTLV-1 infected cells proliferate faster than normal lymphocytes, expand through mitotic division and accumulate genomic lesions. Here, we show that Tax associates with the minichromosome maintenance MCM2-7 helicase complex and localizes to origins of replication. Tax modulates the spatiotemporal program of origin activation and fires supplementary origins at the onset of S phase. Thereby, Tax increases the DNA replication rate, accelerates S phase progression but also generates a replicative stress characterized by the presence of genomic lesions. Mechanistically, Tax favors p300 recruitment and histone hyperacetylation at late replication domains advancing their replication timing in early S phase

Double check - Un concept d'évaluation interactive permettant de distinguer les capacités de compréhension et d'analyse

Comment mesurer aussi systématiquement les trois autres niveaux de la taxonomie de BLOOM que sont (2) la compréhension, (4) l’analyse et (6) l’évaluation ? Ce défi a été affronté à la FAPSE-ULG à l’aide de plusieurs procédures combinées : - les Questions à Choix Multiple (QCM) avec Solutions Générales Implicites (SGI) qui autorisent, en plus des solutions habituellement proposées, les quatre possibilités suivantes : Rejet (aucune solution proposée n’est correcte), Toutes (toutes sont correctes), Manque (il manque des données dans l’énoncé pour que l’on puisse choisir UNE solution comme correcte), Absurdité (il y a une contre-vérité dans l’énoncé à dénoncer en priorité !); - les évaluations à livre ouvert; - les questions en deux volets (double check); - les degrés de certitude. « Double check » (LECLERCQ, 1993), est une procédure d’évaluation interactive, qui consiste à poser une question en deux volets prim et bis. L’étudiant reçoit une première (prim) question (QCM-SGI) où la réponse correcte attendue peut, par exemple, être « 8. Manque de données dans l’énoncé ». Après avoir répondu, l’étudiant reçoit la réponse puis la deuxième partie de la question (bis), par exemple : « quelle donnée manque ?». Suivent à nouveau une série de propositions. Les performances des étudiants se présentent alors selon différents cas de figure qui peuvent ensuite donner lieu à des procédures de remédiation adaptées selon le diagnostic