Prediction and overview of the RpoN-regulon in closely related species of the Rhizobiales

BACKGROUND: In the rhizobia, a group of symbiotic Gram-negative soil bacteria, RpoN (σ(54), σ(N), NtrA) is best known as the sigma factor enabling transcription of the nitrogen fixation genes. Recent reports, however, demonstrate the involvement of RpoN in other symbiotic functions, although no large-scale effort has yet been undertaken to unravel the RpoN-regulon in rhizobia. We screened two complete rhizobial genomes (Mesorhizobium loti, Sinorhizobium meliloti) and four symbiotic regions (Rhizobium etli, Rhizobium sp. NGR234, Bradyrhizobium japonicum, M. loti) for the presence of the highly conserved RpoN-binding sites. A comparison was also made with two closely related non-symbiotic members of the Rhizobiales (Agrobacterium tumefaciens, Brucella melitensis). RESULTS: A highly specific weight-matrix-based screening method was applied to predict members of the RpoN-regulon, which were stored in a highly annotated and manually curated dataset. Possible enhancer-binding proteins (EBPs) controlling the expression of RpoN-dependent genes were predicted with a profile hidden Markov model. CONCLUSIONS: The methodology used to predict RpoN-binding sites proved highly effective as nearly all known RpoN-controlled genes were identified. In addition, many new RpoN-dependent functions were found. The dependency of several of these diverse functions on RpoN seems species-specific. Around 30% of the identified genes are hypothetical. Rhizobia appear to have recruited RpoN for symbiotic processes, whereas the role of RpoN in A. tumefaciens and B. melitensis remains largely to be elucidated. All species screened possess at least one uncharacterized EBP as well as the usual ones. Lastly, RpoN could significantly broaden its working range by direct interfering with the binding of regulatory proteins to the promoter DNA

Monnikerede : the rise and decline of a medieval port community in the Zwin estuary

Historians have primarily considered the small harbour of Monnikerede along the Zwin as an outport in service of Bruges. In this short urban biography, Monnikerede is given the centre stage. We investigate its functional development and changing socio-economic character between the twelfth and fifteenth centuries. Originating before 1200 as a landing stage linked to the Cistercian abbey of Ter Doest, Monnikerede developed into a fairly autonomous fishing and trading port during the thirteenth century. Only after 1300 was the port integrated into a rigid and hierarchical harbour network centred on Bruges, prompting a functional shift towards a staple market and service centre. It was primarily the loss of its privileges during the Bruges revolt of 1436-38 that led to the depopulation and the eventual disappearance of the town

Regulatory Role of Rhizobium etli CNPAF512 fnrN during Symbiosis

The Rhizobium etli CNPAF512 fnrN gene was identified in the fixABCX rpoN(2) region. The corresponding protein contains the hallmark residues characteristic of proteins belonging to the class IB group of Fnr-related proteins. The expression of R. etli fnrN is highly induced under free-living microaerobic conditions and during symbiosis. This microaerobic and symbiotic induction of fnrN is not controlled by the sigma factor RpoN and the symbiotic regulator nifA or fixLJ, but it is due to positive autoregulation. Inoculation of Phaseolus vulgaris with an R. etli fnrN mutant strain resulted in a severe reduction in the bacteroid nitrogen fixation capacity compared to the wild-type capacity, confirming the importance of FnrN during symbiosis. The expression of the R. etli fixN, fixG, and arcA genes is strictly controlled by fnrN under free-living microaerobic conditions and in bacteroids during symbiosis with the host. However, there is an additional level of regulation of fixN and fixG under symbiotic conditions. A phylogenetic analysis of the available rhizobial FnrN and FixK proteins grouped the proteins in three different clusters

Differential Regulation of Rhizobium etli rpoN2 Gene Expression during Symbiosis and Free-Living Growth

The Rhizobium etli rpoN1 gene, encoding the alternative sigma factor ς(54) (RpoN), was recently characterized and shown to be involved in the assimilation of several nitrogen and carbon sources during free-living aerobic growth (J. Michiels, T. Van Soom, I. D’hooghe, B. Dombrecht, T. Benhassine, P. de Wilde, and J. Vanderleyden, J. Bacteriol. 180:1729–1740, 1998). We identified a second rpoN gene copy in R. etli, rpoN2, encoding a 54.0-kDa protein which displays 59% amino acid identity with the R. etli RpoN1 protein. The rpoN2 gene is cotranscribed with a short open reading frame, orf180, which codes for a protein with a size of 20.1 kDa that is homologous to several prokaryotic and eukaryotic proteins of similar size. In contrast to the R. etli rpoN1 mutant strain, inactivation of the rpoN2 gene did not produce any phenotypic defects during free-living growth. However, symbiotic nitrogen fixation was reduced by approximately 90% in the rpoN2 mutant, whereas wild-type levels of nitrogen fixation were observed in the rpoN1 mutant strain. Nitrogen fixation was completely abolished in the rpoN1 rpoN2 double mutant. Expression of rpoN1 was negatively autoregulated during aerobic growth and was reduced during microaerobiosis and symbiosis. In contrast, rpoN2-gusA and orf180-gusA fusions were not expressed aerobically but were strongly induced at low oxygen tensions or in bacteroids. Expression of rpoN2 and orf180 was abolished in R. etli rpoN1 rpoN2 and nifA mutants under all conditions tested. Under free-living microaerobic conditions, transcription of rpoN2 and orf180 required the RpoN1 protein. In symbiosis, expression of rpoN2 and orf180 occurred independently of the rpoN1 gene, suggesting the existence of an alternative symbiosis-specific mechanism of transcription activation

Liens entre variables sociopsychologiques et localisations des TMS

info:eu-repo/semantics/publishe

Liens entre variables sociopsychologiques et localisations des TMS

Les associations entre les troubles musculosquelettiques des membres supérieurs (TMSms) et des variables sociopsychologiques telles que des facteurs de personnalité, les styles professionnels, des astreintes somatiques et les dimensions contrôle-demandes de Karasek sont étudiées. Les résultats montrent que des liens significatifs sont présents, mais que ces liens sont différents suivant la localisation de la pathologie :il semble que le niveau de névrosisme ait une influence sur la présence des TMS de la nuque et du bas du dos, et que le comportement de type A ait une influence sur la présence de TMS du poignet dominant.info:eu-repo/semantics/publishe

Musculo-skeletal disorders, physical fatigue, mental fatigue and perceived work constraints.

info:eu-repo/semantics/publishe

Turning back the tide: the Zwin debate in perspective : a historiographical review of the medieval port system northeast of Bruges

A long with the rise and fall of medieval Bruges, a linear gateway to the North Sea was linked, embanked and flanked with channels, dikes and harbours, creating a historical landscape that is marked by the dynamic interaction between men and nature. The aim of this paper is to provide a critical review of previous and current approaches to the evolution of the medieval port. Nearly 150 years of research has been divided into four characteristic phases in order to construct a general overview. Two significant landscape elements have been studied in detail in order to expose the specific shortcomings of the research thus far. This study demonstrates that the Zwin debate is outdated and has not kept up with state-of-the-art research trends and techniques. Moreover, it shows that the historical geography of the region has been inadequately interpreted in accordance with the latest geomorphological and archaeological findings

Defence of Rhizobium etli bacteroids against oxidative stress involves a complexly regulated atypical 2-Cys peroxiredoxin

In general, oxidative stress, the consequence of an aerobic lifestyle, induces bacterial antioxidant defence enzymes. Here we report on a peroxiredoxin of Rhizobium etli, prxS, strongly expressed under microaerobic conditions and during the symbiotic interaction with Phaseolus vulgaris. The microaerobic induction of the prxS-rpoN2 operon is mediated by the alternative sigma factor RpoN and the enhancer-binding protein NifA. The RpoN-dependent promoter is also active under low-nitrogen conditions through the enhancer-binding protein NtrC. An additional symbiosis-specific weak promoter is located between prxS and rpoN2. Constitutive expression of prxS confers enhanced survival and growth to R. etli in the presence of H2O2. Single prxS mutants are not affected in their symbiotic abilities or defence response against oxidative stress under free-living conditions. In contrast, a prxS katG double mutant has a significantly reduced (>40%) nitrogen fixation capacity, suggesting a functional redundancy between PrxS and KatG, a bifunctional catalase-peroxidase. In vitro assays demonstrate the reduction of PrxS protein by DTT and thioredoxin. PrxS displays substrate specificity towards H2O2 (Km = 62 microM) over alkyl hydroperoxides (Km > 1 mM). Peroxidase activity is abolished in both the peroxidatic (C56) and resolving (C156) cysteine PrxS mutants, while the conserved C81 residue is required for proper folding of the protein. Resolving of the R. etli PrxS peroxidatic cysteine is probably an intramolecular process and intra- and intersubunit associations were observed. Taken together, our data support, for the first time, a role for an atypical 2-Cys peroxiredoxin against oxidative stress in R. etli bacteroids.status: publishe