Regulation of the Gac/Rsm pathway in "Pseudomonas fluorescens" CHA0

SUMMARY : Two-component systems are key mediators implicated in the response of numerous bacteria to a wide range of signals and stimuli. The two-component system comprised of the sensor kinase GacS and the response regulator GacA is broadly distributed among γ-proteobacteria bacteria and fulfils diverse functions such as regulation of carbon storage and expression of virulence. In Pseudomonas fluorescens, a soil bacterium which protects plants from root-pathogenic fungi and nematodes, the GacS/GacA two-component system has been shown to be essential for the production of secondary metabolites and exoenzymes required for the biocontrol activity of the bacterium. The regulatory cascade initiated by GacS/GacA consists of two translational repressor proteins, RsmA and RsmE, as well as three GacAcontrolled small regulatory RNAs RsmX, RsmY and RsmZ, which titrate RsmA and RsmE to allow the expression of biocontrol factors. Genetic analysis revealed that two additional sensor kinases termed RetS and Lads were involved as negative and positive control elements, respectively, in the Gac/Rsm pathway in P. fluoresens CHAO. Furthermore, it could be proposed that RetS and Lads interact with GacS, thereby modulating the expression of antibiotic compounds and hydrogen cyanide, as well as the rpoS gene encoding the stress and stationary phase sigma factor σ. Temperature was found to be an important environmental cue that influences the Gac/Rsm network. Indeed, the production of antibiotic compounds and hydrogen cyanide was reduced at 35°C, by comparison with the production at 30°C. RetS was identified to be involved in this temperature control. The small RNA RsmY was confirmed to be positively regulated by GacA and RsmA/RsmE. Two essential regions were identified in the rsmY promoter by mutational analysis, the upstream activating sequence (UAS) and the linker sequence. Although direct experimental evidence is still missing, several observations suggest that GacA may bind to the UAS, whereas the linker region would be recognized by intermediate RsmA/RsmEdependent repressors and/or activators. In conclusion, this work has revealed new elements contributing to the function of the signal transduction mechanisms in the Gac/Rsm pathway. RESUME : Les systèmes ä deux composants sont des mécanismes d'une importance notoire que beaucoup de bactéries utilisent pour faire face et répondre aux stimuli environnementaux. Le système à deux composants comprenant le senseur GacS et le régulateur de réponse GacA est très répandu chez les γ-protéobactéries et remplit des fonctions aussi diverses que la régulation du stockage de carbone ou l'expression de la virulence. Chez Pseudomonas fluorescens CHAO, une bactérie du sol qui protège les racines des plantes contre des attaques de champignons et nématodes pathogènes, le système à deux composants GacS/GacA est essentiel à la production de métabolites secondaires et d'exoenzymes requis pour l'activité de biocontrôle de la bactérie. La cascade régulatrice initiée pas GacS/GacA fait intervenir deux protéines répresseur de traduction, RsmA et RsmE, ainsi que trois petits ARNs RsmX, RsmY et RsmZ, dont la production est contrôlée par GacA. Ces petits ARNs ont pour rôle de contrecarrer l'action des protéines répressseur de la traduction, ce qui permet l'expression de facteurs de biocontrôle. Des analyses génétiques ont révélé la présence de deux senseurs supplémentaires, appelés Rets et Lads, qui interviennent dans la cascade Gac/Rsm de P. fluorescens. L'impact de ces senseurs est, respectivement, négatif et positif. Ces interactions ont apparenunent lieu au niveau de GacS et permettent une modulation de l'expression des antibiotiques et de l'acide cyanhydrique, ainsi que du gène rpoS codant pour le facteur sigma du stress. La température s'est révélée être un facteur environnemental important qui influence la cascade Gac/Rsm. Il s'avère en effet que la production d'antibiotiques ainsi que d'acide cyanhydrique est moins importante à 35°C qu'à 30°C. L'implication du senseur Rets dans ce contrôle par la température a pu être démontrée. La régulation positive du petit ARN RsmY par GacA et RsmA/RsmE a pu être confirmée; par le biais d'une analyse mutationelle, deux régions essentielles ont pu être mises en évidence dans la région promotrice de rsmY. Malgré le manque de preuves expérimentales directes, certains indices suggèrent que GacA puisse directement se fixer sur une des deux régions (appelée UAS), tandis que la deuxième région (appelée linker) serait plutôt reconnue par des facteurs intermédiaires (activateurs ou répresseurs) dépendant de RsmA/RsmE. En conclusion, ce travail a dévoilé de nouveaux éléments permettant d'éclairer les mécanismes de transduction des signaux dans la cascade Gac/Rsm.

A comparative study of the preventative effects exerted by two probiotics, Lactobacillus reuteri and Lactobacillus fermentum, in the trinitrobenzenesulfonic acid model of rat colitis

The intestinal anti-inflammatory effects of two probiotics isolated from breast milk, Lactobacillus reuteri and L. fermentum, were evaluated and compared in the trinitrobenzenesulfonic acid (TNBS) model of rat colitis. Colitis was induced in rats by intracolonic administration of 10 mg TNBS dissolved in 50% ethanol (0.25 ml). Either L. reuteri or L. fermentum was daily administered orally (5 x 10(8) colony-forming units suspended in 0.5 ml skimmed milk) to each group of rats (n 10) for 3 weeks, starting 2 weeks before colitis induction. Colonic damage was evaluated histologically and biochemically, and the colonic luminal contents were used for bacterial studies and for SCFA production. Both probiotics showed intestinal anti-inflammatory effects in this model of experimental colitis, as evidenced histologically and by a significant reduction of colonic myeloperoxidase activity (P<0.05). L. fermentum significantly counteracted the colonic glutathione depletion induced by the inflammatory process. In addition, both probiotics lowered colonic TNFalpha levels (P<0.01) and inducible NO synthase expression when compared with non-treated rats; however, the decrease in colonic cyclo-oxygenase-2 expression was only achieved with L.fermentum administration. Finally, the two probiotics induced the growth of Lactobacilli species in comparison with control colitic rats, but the production of SCFA in colonic contents was only increased when L. fermentum was given. In conclusion, L. fermentum can exert beneficial immunomodulatory properties in inflammatory bowel disease, being more effective than L. reuteri, a probiotic with reputed efficacy in promoting beneficial effects on human health.

Two approaches to discovering and developing new drugs for Chagas disease

This review will focus on two general approaches carried out at the Sandler Center, University of California, San Francisco, to address the challenge of developing new drugs for the treatment of Chagas disease. The first approach is target-based drug discovery, and two specific targets, cytochrome P450 CYP51 and cruzain (aka cruzipain), are discussed. A "proof of concept" molecule, the vinyl sulfone inhibitor K777, is now a clinical candidate. The preclinical assessment compliance for filing as an Investigational New Drug with the United States Food and Drug Administration (FDA) is presented, and an outline of potential clinical trials is given. The second approach to identifying new drug leads is parasite phenotypic screens in culture. The development of an assay allowing high throughput screening of Trypanosoma cruzi amastigotes in skeletal muscle cells is presented. This screen has the advantage of not requiring specific strains of parasites, so it could be used with field isolates, drug resistant strains or laboratory strains. It is optimized for robotic liquid handling and has been validated through a screen of a library of FDA-approved drugs identifying 65 hits.

Bat flies on phyllostomid hosts in the Cerrado region: component community, prevalence and intensity of parasitism

Streblidae flies are specialised parasites of bat hosts, mainly phyllostomids. There is a high richness of streblids in the savannah-like Cerrado region; however, there is little quantitative data available in parasitological indices. Here, we describe the component community, prevalence and intensity of a streblid infestation on a phyllostomid bat assemblage in Serra da Bodoquena, a Cerrado region in Southwest Brazil. We conducted surveys by capturing and inspecting bat hosts during the seven-month period between October 2004-December 2005. All the ectoparasites found on the bats were collected in the field and then counted and identified in the laboratory. We captured 327 bats belonging to 13 species, of which eight species were parasitized by 17 species of streblids. Carollia perspicillata and Glossophaga soricina were infested with seven streblid species, whereas the other bat species were infested with four or fewer streblid species. Megistopoda proxima and Aspidoptera falcata flies were found on Sturnira lilium, and Trichobius joblingi was the most prevalent fly on C. perspicillata. Megistopoda aranea and Aspidoptera phyllostomatis were highly prevalent and had a high intensity of infestation on Artibeus planirostris. Overall comparisons of the available data suggest that the component communities of streblids vary more between the Cerrado and Atlantic Forest phytogeographical regions than between localities within the same phytogeographical region.

Lien entre durée de séjour et réadmissions en chirurgie et en obstétrique: étude de deux procédures à partir des données du PMSI = Using administrative data to assess the impact of length of stay on readmissions: study of two procedures in surgery and obstetrics

Position du problème: La mise en place de la tarification à l'activité pour les hôpitaux de court séjour pourrait entraîner une diminution des durées de séjour pour raisons financières. L'impact potentiel de ce phénomène sur la qualité des soins n'est pas connu. Les réadmissions identifiées à l'aide des données administratives hospitalières sont, pour certaines situations cliniques, des indicateurs de qualité des soins valides. Méthode: Étude rétrospective du lien entre la durée de séjour et la survenue de réadmissions imprévues liées au séjour initial, pour les cholécystectomies simples et les accouchements par voie basse sans complication, à partir des données du programme de médicalisation des systèmes d'information de l'Assistance publique-Hôpitaux de Paris des années 2002 à 2005. Résultats: Pour les deux procédures, la probabilité de réadmission suit une courbe en " J ". Après ajustement sur l'âge, le sexe, les comorbidités associées, l'hôpital et l'année d'admission, la probabilité de réadmission est plus élevée pour les durées de séjour les plus courtes : pour les cholécystectomies, odds ratio : 6,03 [IC95 % : 2,67-13,59] pour les hospitalisations d'un jour versus trois jours ; pour les accouchements, odds ratio : 1,74 [IC95 % : 1,05-2,91] pour les hospitalisations de deux jours versus trois jours. Conclusion: Pour deux pathologies communes, les durées de séjour les plus courtes sont associées à des probabilités de réadmission plus élevées. L'utilisation routinière des données du programme de médicalisation des systèmes d'information peut permettre d'assurer le suivi de la relation entre la réduction de la durée de séjour et les réadmissions. The prospective payment system for the French short-stay hospitals creates a financial incentive to reduce length of stay. The potential impact of the resulting decrease in length of stay on the quality of healthcare is unknown. Readmission rates are valid outcome indicators for some clinical procedures. Methods: Retrospective study of the association between length of stay and unplanned readmissions related to the initial stay, for two procedures: cholecystectomy and vaginal delivery. Data: Administrative diagnosis-related groups database of "Assistance publique-Hopitaux de Paris", a large teaching hospital, for years 2002 to 2005. Results: The risk of readmission according to length of stay, taking age, sex, comorbidity, hospital and year of admission into account, followed a J-shaped curve for both procedures. The probability of readmission was higher for very short stays, with odds ratios and 95% confidence intervals of 6.03 [2.67-13.59] for cholecystectomies (1- versus 3-night stays), and of 1.74 [1.05-2.91] for vaginal deliveries (2- versus 3-night stays). Conclusion: For both procedures, the shortest lengths of stay are associated with a higher readmission probability. Suitable indicators derived from administrative databases would enable monitoring of the association between length of stay and readmissions.

Spotting Translationese in two Corpora of Original and Translated Catalan Texts: an Empirical Approach

This research investigates the phenomenon of translationese in two monolingual comparable corpora of original and translated Catalan texts. Translationese has been defined as the dialect, sub-language or code of translated language. This study aims at giving empirical evidence of translation universals regardless the source language.Traditionally, research conducted on translation strategies has been mainly intuition-based. Computational Linguistics and Natural Language Processing techniques provide reliable information of lexical frequencies, morphological and syntactical distribution in corpora. Therefore, they have been applied to observe which translation strategies occur in these corpora.Results seem to prove the simplification, interference and explicitation hypotheses, whereas no sign of normalization has been detected with the methodology used.The data collected and the resources created for identifying lexical, morphological and syntactic patterns of translations can be useful for Translation Studies teachers, scholars and students: teachers will have more tools to help students avoid the reproduction of translationese patterns. Resources developed will help in detecting non-genuine or inadequate structures in the target language. This fact may imply an improvement in stylistic quality in translations. Translation professionals can also take advantage of these resources to improve their translation quality.

The INTERNORM project : bridging two worlds of expert- and layknowledge in standardization

This paper presents a pilot project to reinforce participatory practices in standardization. The INTERNORM project is funded by the University of Lausanne, Switzerland. It aims to create an interactive knowledge center based on the sharing of academic skills and the experiences accumulated by the civil society, especially consumer associations, environmental associations and trade unions to strengthen the participatory process of standardization. The first objective of the project is action-oriented: INTERNORM provides a common knowledge pool supporting the participation of civil society actors to international standard-setting activities by bringing them together with academic experts in working groups and by providing logistic and financial support to their participation to meetings of national and international technical committees. The second objective of the project is analytical: the standardization action initiated through INTERNORM provides a research field for a better understanding of the participatory dynamics underpinning international standardization. The paper presents three incentives that explain civil society (non-)involvement in standardization that try to overcome conventional resource-based hypotheses: an operational incentive, related to the use of standards in the selective goods provided by associations to their membership; a thematic incentive, provided by the setting of priorities by strategic committees created in some standardization organization; a rhetorical incentive, related to the discursive resource that civil society concerns offers to the different stakeholders.

One, two, (three), infinity: Newspaper and lab beauty-contest experiments

"Beauty-contest" is a game in which participants have to choose, typically, a number in [0,100], the winner being the person whose number is closest to a proportion of the average of all chosen numbers. We describe and analyze Beauty-contest experiments run in newspapers in UK, Spain, and Germany and find stable patterns of behavior across them, despite the uncontrollability of these experiments. These results are then compared with lab experiments involving undergraduates and game theorists as subjects, in what must be one of the largest empirical corroborations of interactive behavior ever tried. We claim that all observed behavior, across a wide variety of treatments and subject pools, can be interpretedas iterative reasoning. Level-1 reasoning, Level-2 reasoning and Level-3 reasoning are commonly observed in all the samples, while the equilibrium choice (Level-Maximum reasoning) is only prominently chosen by newspaper readers and theorists. The results show the empirical power of experiments run with large subject-pools, and open the door for more experimental work performed on the rich platform offered by newspapers and magazines.

Bionomy of two flies of sanitary and forensic importance: Peckia (Sarcodexia) lambens (Wiedemann) and Oxysarcodexia amorosa (Schiner) (Diptera, Sarcophagidae)

ABSTRACTThis study aims to elucidate the bionomy of Peckia(Sarcodexia) lambens and Oxysarcodexia amorosa to provide data for medical, veterinary and forensic entomology analyses. We analyzed larval stage duration (L1–L3), weight of the mature larvae (L3), pupal stage duration, L1–adult duration, adult emergence and viability of larvae and adults of both species. Larval viability of P. (S.) lambens was 82% and the mean duration of the larval stage was 3.51 ± 0.99 days. The mature larvae had a mean weight of 33.67 ± 7.13 mg. The mean duration of the pupal stage was 8.26 ± 0.93 days and the mean duration of the L1–adult was 11.53 ± 1.22 days. Mean lifespan for females and males was 39.33 ± 1.52 and 57.33 ± 4.72 days, respectively. Larval viability of O. amorosa was 76% and mean duration of larval stage was 3.51 ± 0.64 days. Mature larvae had a mean weight of 28.28 ± 3.38 mg. Mean duration of the pupal stage was 10.14 ± 0.63 days and mean duration of the L1–adult was 13.60 ± 0.69 days. Mean lifespan for females and males was 83.66 ± 15.94 and 84.00 ± 19.97 days, respectively. Oxysarcodexia amorosa showed a L1–adult stage longer than P. (S.) lambens; however both species showed low viability. O. amorosa laid more larvae than P. (S.) lambens, this fact may occur because O. amorosa had longer life duration.

Design of new promoters and of a dual-bioreporter based on cross-activation by the two regulatory proteins XylR and HbpR.

The HbpR protein is the sigma54-dependent transcription activator for 2-hydroxybiphenyl degradation in Pseudomonas azelaica. The ability of HbpR and XylR, which share 35% amino acid sequence identity, to cross-activate the PhbpC and Pu promoters was investigated by determining HbpR- or XylR-mediated luciferase expression and by DNA binding assays. XylR measurably activated the PhbpC promoter in the presence of the effector m-xylene, both in Escherichia coli and Pseudomonas putida. HbpR weakly stimulated the Pu promoter in E. coli but not in P. azelaica. Poor HbpR-dependent activation from Pu was caused by a weak binding to the operator region. To create promoters efficiently activated by both regulators, the HbpR binding sites on PhbpC were gradually changed into the XylR binding sites of Pu by site-directed mutagenesis. Inducible luciferase expression from mutated promoters was tested in E. coli on a two plasmid system, and from mono copy gene fusions in P. azelaica and P. putida. Some mutants were efficiently activated by both HbpR and XylR, showing that promoters can be created which are permissive for both regulators. Others achieved a higher XylR-dependent transcription than from Pu itself. Mutants were also obtained which displayed a tenfold lower uninduced expression level by HbpR than the wild-type PhbpC, while keeping the same maximal induction level. On the basis of these results, a dual-responsive bioreporter strain of P. azelaica was created, containing both XylR and HbpR, and activating luciferase expression from the same single promoter independently with m-xylene and 2-hydroxybiphenyl.

Iowa Leading Indicators Index after Two Years: An Assessment and Update

The Iowa Leading Indicators Index (ILII) Annual Assessment and Update assesses how well the ILII has met the goals behind its development, gauges the validity of the existing components, considers additional components that have been suggested along the way, and carries out the annual updates necessary for such an index.

Nutrient supply by mass flow and diffusion to maize plants in response to soil aggregate size and water potential

Nutrients are basically transported to the roots by mass flow and diffusion. The aim of this study was to quantify the contribution of these two mechanisms to the acquisition of macronutrients (N, P, K, Ca, Mg, and S) and cationic micronutrients (Fe, Mn, Zn, and Cu) by maize plants as well as xylem exudate volume and composition in response to soil aggregate size and water availability. The experiment was conducted in a greenhouse with samples of an Oxisol, from under two management systems: a region of natural savanna-like vegetation (Cerradão, CER) and continuous maize under conventional management for over 30 years (CCM). The treatments were arranged in a factorial [2 x (1 + 2) x 2] design, with two management systems (CER and CCM), (1 + 2) soil sifted through a 4 mm sieve and two aggregate classes (< 0.5 mm and 0.5 - 4.0 mm) and two soil matric potentials (-40 and -10 kPa). These were evaluated in a randomized block design with four replications. The experiment was conducted for 70 days after sowing. The influence of soil aggregate size and water potential on the nutrient transport mechanisms was highest in soil samples with higher nutrient concentrations in solution, in the CER system; diffusion became more relevant when water availability was higher and in aggregates < 0.5 mm. The volume of xylem exudate collected from maize plants increased with the decrease in aggregate size and the increased availability of soil water in the CER system. The highest Ca and Mg concentrations in the xylem exudate of plants grown on samples from the CER system were related to the high concentrations of these nutrients in the soil solution of this management system.

CHARACTERIZATION OF NrsZ, A NOVEL SMALL REGULATORY NON-CODING RNA INVOLVED IN THE ADAPTATION OF PSEUDOMONAS AERUGINOSA PAO1

The opportunistic ubiquitous pathogen Pseudomonas aeruginosa strain PAOl is a versatile Gram-negative bacterium that has the extraordinary capacity to colonize a wide diversity of ecological niches and to cause severe and persistent infections in humans. To ensure an optimal coordination of the genes involved in nutrient utilization, this bacterium uses the NtrB/C and/or the CbrA/B two-component systems, to sense nutrients availability and to regulate in consequence the expression of genes involved in their uptake and catabolism. NtrB/C is specialized in nitrogen utilization, while the CbrA/B system is involved in both carbon and nitrogen utilization and both systems activate their target genes expression in concert with the alternative sigma factor RpoN. Moreover, the NtrB/C and CbrA/B two- component systems regulate the secondary metabolism of the bacterium, such as the production of virulence factors. In addition to the fine-tuning transcriptional regulation, P. aeruginosa can rapidly modulate its metabolism using small non-coding regulatory RNAs (sRNAs), which regulate gene expression at the post-transcriptional level by diverse and sophisticated mechanisms and contribute to the fast physiological adaptability of this bacterium. In our search for novel RpoN-dependent sRNAs modulating the nutritional adaptation of P. aeruginosa PAOl, we discovered NrsZ (Nitrogen regulated sRNA), a novel RpoN-dependent sRNA that is induced under nitrogen starvation by the NtrB/C two-component system. NrsZ has a unique architecture, formed of three similar stem-loop structures (SL I, II and II) separated by variant spacer sequences. Moreover, this sRNA is processed in short individual stem-loop molecules, by internal cleavage involving the endoribonuclease RNAse E. Concerning NrsZ functions in P. aeruginosa PAOl, this sRNA was shown to trigger the swarming motility and the rhamnolipid biosurfactants production. This regulation is due to the NrsZ-mediated activation of rhlA expression, a gene encoding for an enzyme essential for swarming motility and rhamnolipids production. Interestingly, the SL I structure of NrsZ ensures its regulatory function on rhlA expression, suggesting that the similar SLs are the functional units of this modular sRNA. However, the regulatory mechanism of action of NrsZ on rhlA expression activation remains unclear and is currently being investigated. Additionally, the NrsZ regulatory network was investigated by a transcriptome analysis, suggesting that numerous genes involved in both primary and secondary metabolism are regulated by this sRNA. To emphasize the importance of NrsZ, we investigated its conservation in other Pseudomonas species and demonstrated that NrsZ is conserved and expressed under nitrogen limitation in Pseudomonas protegens Pf-5, Pseudomonas putida KT2442, Pseudomonas entomophila L48 and Pseudomonas syringae pv. tomato DC3000, strains having different ecological features, suggesting an important role of NrsZ in the adaptation of Pseudomonads to nitrogen starvation. Interestingly the architecture of the different NrsZ homologs is similarly composed by SL structures and variant spacer sequences. However, the number of SL repetitions is not identical, and one to six SLs were predicted on the different NrsZ homologs. Moreover, NrsZ is processed in short molecules in all the strains, similarly to what was previously observed in P. aeruginosa PAOl, and the heterologous expression of the NrsZ homologs restored rhlA expression, swarming motility and rhamnolipids production in the P. aeruginosa NrsZ mutant. In many aspects, NrsZ is an atypical sRNA in the bacterial panorama. To our knowledge, NrsZ is the first described sRNA induced by the NtrB/C. Moreover, its unique modular architecture and its processing in similar short SL molecules suggest that NrsZ belongs to a novel family of bacterial sRNAs. -- L'agent pathogène opportuniste et ubiquitaire Pseudomonas aeruginosa souche PAOl est une bactérie Gram négative versatile ayant l'extraordinaire capacité de coloniser différentes niches écologiques et de causer des infections sévères et persistantes chez l'être humain. Afin d'assurer une coordination optimale des gènes impliqués dans l'utilisation de différents nutriments, cette bactérie se sert de systèmes à deux composants tel que NtrB/C et CbrA/B afin de détecter la disponibilité des ressources nutritives, puis de réguler en conséquence l'expression des gènes impliqués dans leur importation et leur catabolisme. Le système NtrB/C régule l'utilisation des sources d'azote alors que le système CbrA/B est impliqué à la fois dans l'utilisation des sources de carbone et d'azote. Ces deux systèmes activent l'expression de leurs gènes-cibles de concert avec le facteur sigma alternatif RpoN. En outre, NtrB/C et CbrA/B régulent aussi le métabolisme secondaire, contrôlant notamment la production d'importants facteurs de virulence. En plus de toutes ces régulations génétiques fines ayant lieu au niveau transcriptionnel, P. aeruginosa est aussi capable de moduler son métabolisme en se servant de petits ARNs régulateurs non-codants (ARNncs), qui régulent l'expression génétique à un niveau post- transcriptionnel par divers mécanismes sophistiqués et contribuent à rendre particulièrement rapide l'adaptation physiologique de cette bactérie. Au cours de nos recherches sur de nouveaux ARNncs dépendant du facteur sigma RpoN et impliqués dans l'adaptation nutritionnelle de P. aeruginosa PAOl, nous avons découvert NrsZ (Nitrogen regulated sRNA), un ARNnc induit par la cascade NtrB/C-RpoN en condition de carence en azote. NrsZ a une architecture unique, composée de trois structures en tige- boucle (TB I, II et III) hautement similaires et séparées par des « espaceurs » ayant des séquences variables. De plus, cet ARNnc est clivé en petits fragments correspondant au trois molécules en tige-boucle, par un processus de clivage interne impliquant l'endoribonucléase RNase E. Concernant les fonctions de NrsZ chez P. aeruginosa PAOl, cet ARNnc est capable d'induire la motilité de type « swarming » et la production de biosurfactants, nommés rhamnolipides. Cette régulation est due à l'activation par NrsZ de l'expression de rhlA, un gène essentiel pour la motilité de type swarming et pour la production de rhamnolipides. Étonnamment, la structure TB I est capable d'assurer à elle seule la fonction régulatrice de NrsZ sur l'expression de rhlA, suggérant que ces molécules TBs sont les unités fonctionnelles de cet ARNnc modulaire. Cependant, le mécanisme moléculaire par lequel NrsZ active l'expression de rhlA demeure à ce jour incertain et est actuellement à l'étude. En plus, le réseau de régulations médiées par NrsZ a été étudié par une analyse de transcriptome qui a indiqué que de nombreux gènes impliqués dans le métabolisme primaire ou secondaire seraient régulés par NrsZ. Pour accentuer l'importance de NrsZ, nous avons étudié sa conservation dans d'autres espèces de Pseudomonas. Ainsi, nous avons démontré que NrsZ est conservé et exprimé en situation de carence d'azote par les souches Pseudomonas protegens Pf-5, Pseudomonas putida KT2442, Pseudomonas entomophila L48, Pseudomonas syringae pv. tomato DC3000, quatre espèces ayant des caractéristiques écologiques très différentes, suggérant que NrsZ joue un rôle important dans l'adaptation du genre Pseudomonas envers la carence en azote. Chez toutes les souches étudiées, les différents homologues de NrsZ présentent une architecture similaire faite de TBs conservées et d'espaceurs. Cependant, le nombre de TBs n'est pas identique et peut varier de une à six copies selon la souche. Les différentes versions de NrsZ sont clivées en petites molécules dans ces quatre souches, comme il a été observé chez P. aeruginosa PAOl. De plus, l'expression hétérologue des différentes variantes de NrsZ est capable de restaurer l'expression de rhlA, la motilité swarming et la production de rhamnolipides dans une souche de P. aeruginosa dont nrsZ a été inactivé. Par bien des aspects, NrsZ est un ARNnc atypique dans le monde bactérien. À notre connaissance, NrsZ est le premier ARNnc décrit comme étant régulé par le système NtrB/C. De plus, son unique architecture modulaire et son clivage en petites molécules similaires suggèrent que NrsZ appartient à une nouvelle famille d'ARNncs bactériens.

The effect of two pesticides (Vitavax-300 and Gaucho) on rhizobia and on the nodulation of four legumes

Selostus: Kasvinsuojeluaineiden Vitavax-300 ja Gaucho vaikutus juurinystyräbakteerin kasvuun ja neljän palkokasvin nystyröitymiseen

Nitrogen fertilization (15NH4NO3) of palisadegrass and residual effect on subsequent no-tillage corn

Nitrogen is required in large amounts by plants and their dinamics in corn and perennial forages intercropped is little known. This study analyzed the efficiency of nitrogen fertilization (15NH4NO3) applied after corn grain harvest to palisadegrass (Brachiaria brizantha cv. Marandu) in intercrops sown at two times, as well as the N residual effect on the subsequent corn crop. The field experiment was performed in Botucatu, São Paulo State, in southeastern Brazil, on a structured Alfisol under no-tillage. The experiment was arranged in a randomized block design in a split plot scheme with four replications. The main plots consisted of two intercropping systems (corn and palisadegrass sown together and palisadegrass sown later, at corn top-dressing fertilization). The subplots consisted of four N rates (0, 30, 60, and 120 kg ha-1 N). The subplots contained microplots, in which enriched ammonium nitrate (15NH4NO3) was applied at the same rates. The time of intercrop sowing affected forage dry matter production, the amount of fertilizer-derived N in and the N use efficiency by the forage plants. Nitrogen applied in autumn to palisadegrass intercropped with corn, planted either at corn sowing or at N top-dressing fertilization, increased the forage yield up to a rate of 60 kg ha-1. The amount of fertilizer-derived N by the forage plants and the fertilizer use efficiency by palisadegrass were highest 160 days after fertilization for both intercrop sowing times, regardless of N rates. Residual N did not affect the N nutrition of corn plants grown in succession to palisadegrass, but increased grain yield at rates of 60 and 120 kg ha-1 N, when corn was grown on palisadegrass straw from the intercrop installed at corn fertilization (top-dressing). Our results indicated that the earlier intercropping allowed higher forage dry matter production. On the other hand, the later intercrop allowed a higher corn grain yield in succession to N-fertilized palisadegrass.