1,721,045 research outputs found
SMALL RNAS AND REGULATION OF VIRULENCE TRAITS IN PSEUDOMONAS AERUGINOSA
Full text linkThis PhD project aimed at the functional characterization of novel Pseudomonas aeruginosa
small RNAs (sRNAs) involved in virulence-associated regulatory networks. Following an
initial phase of screenings for sRNA candidates involved in the regulation of virulence traits,
the work focused on the sRNAs SPA0122 and SPA0084.
SPA0122, renamed ErsA, is transcribed from the same genomic context of the well-known
Escherichia coli Spot 42. We show that, different from Spot 42, ErsA is under the
transcriptional control of the envelope stress response, which is known to impact the
pathogenesis of P. aeruginosa through the activity of the alternative sigma factor σ22. The
transcriptional responsiveness of ErsA RNA also spans infection-relevant cues that P.
aeruginosa can experience in mammalian hosts, such as limited iron availability, temperature
shifts from environmental to body temperature and reduced oxygen conditions. Another
difference between Spot 42 and ErsA is that ErsA does not seem to be involved in the
regulation of carbon source catabolism. Instead, our results suggest that ErsA is linked to
anabolic functions for the synthesis of exoproducts from sugar precursors. We show that ErsA
directly operates in the negative post-transcriptional regulation of the algC gene that encodes
the virulence-associated enzyme AlgC, which provides sugar precursors for the synthesis of
several P. aeruginosa polysaccharides. Like ErsA, the activation of algC expression is also
dependent on σ22. Altogether, our results suggest that ErsA and σ22 combine in an incoherent
feed-forward loop to fine-tune AlgC enzyme expression.
As regards SPA0084, our results indicate that is embedded in the P. aeruginosa quorum
sensing (QS) with the role of wiring las to pqs systems. In fact, we show that SPA0084
responds to the las regulator LasR and impacts positively the synthesis of the pqs quinolone
signal PQS. Our results suggest that the stimulation of PQS synthesis is mediated by a positive
post-transcriptional effect of SPA0084 on the pqsC gene belonging to the pqsABCD cluster
involved in the biosynthesis of the PQS-precursor HHQ. We suggest that a fine balancing
between the different already known regulatory effects of LasR on PQS synthesis and this one
mediated by SPA0084 can influence timing and magnitude of expression of QS-regulated
virulence factors. This view is consistent with the evidence that perturbations of SPA0084
levels affect pyocyanin synthesis, biofilm formation and swarming motility, processes that are
known to be influenced by PQS synthesis. Besides being regulated by LasR, SPA0084 responds
to infection relevant cues that P. aeruginosa can experience in mammalian hosts such as temperature and oxygen availability. Furthermore, SPA0084 shows a growth phasedependent
pattern of expression, being up-regulated in stationary phase. Sequence analysis of
the spa0084 promoter region strongly suggests that the growth phase-dependent pattern of
SPA0084 expression is due to the activity of the alternative σ factor RpoS whose significance
as global factor controlling quorum sensing gene expression was shown previously. Together,
these SPA0084 regulations are expected to contribute to the fine co-modulation of PQS
synthesis
Involvement of the conserved small RNA SPA0122 in the regulation of virulence traits of Pseudomonas aeruginosa
No full textCrucial traits contributing to pathogenicity of Pseudomonas aeruginosa are the production of a large assortment of virulence factors, biofilm formation and the ability to rapidly develop resistance to multiple classes of antibiotics. Expression of these traits is fine-tuned by a dynamic and intricate regulatory network [1], in which more than 50 regulatory proteins play key roles as transcription regulators. The involvement of small RNAs (sRNAs) in the P. aeruginosa virulence regulatory network has been underestimated, being so far less than ten the sRNAs shown to be implicated. We have recently performed a comparative sRNA profiling via deep-sequencing of P. aeruginosa PAO1 and PA14 strains [2] which share the same host range but differ in pathogenicity. We now aim to unravel virulence-relevant sRNA-based regulatory systems throughout the panel of novel sRNAs that we have identified. In this study, we have collected evidences for the involvement of the conserved sRNA SPA0122 in the regulation of two typical P. aeruginosa virulence traits: swimming motility and production of pyocyanin. In addition, we suggest that SPA0122 negatively regulates the expression of i) a key enzyme providing sugar precursors for the synthesis of exopolysaccarides, one of the biofilm matrix components, and ii) a protein involved in antibiotic susceptibility. Finally, we have evidences that SPA0122 is responsive to infection-relevant host stimuli such as oxygen availability and shift from room to body temperature.
In conclusion, our results indicate that SPA0122, once receiving inputs from host sensing/signaling pathways, plays a role as global co-mediator of complex virulence regulatory sub-networks.
1. Balasubramanian D, Schneper L, Kumari H & Mathee K (2013) A dynamic and intricate regulatory network determines Pseudomonas aeruginosa virulence. Nucleic Acids Res, 41:1-20.
2. Ferrara S, Brugnoli M, De Bonis A, Righetti F, Delvillani F, Dehò G, Horner D, Briani F & Bertoni G (2012) Comparative Profiling of Pseudomonas aeruginosa Strains Reveals Differential Expression of Novel Unique and Conserved Small RNAs. PLoS One, 7:e36553
Involvement of the conserved small RNA SPA0122 in the regulation of virulence traits of the opportunistic pathogen Pseudomonas aeruginosa
No full textPseudomonas aeruginosa is an important opportunistic pathogen in immune-compromised and cystic fibrosis patients, responsible for numerous acute and chronic infections. Crucial traits contributing to pathogenicity of P. aeruginosa are the production of a large assortment of virulence factors, biofilm formation and the ability to rapidly develop resistance to multiple classes of antibiotics. Expression of these traits is fine-tuned by a dynamic and intricate regulatory network [1], in which more than 50 regulatory proteins play key roles as transcription regulators. The involvement of small RNAs (sRNAs) in the P. aeruginosa virulence regulatory network has been underestimated, being so far less than ten the sRNAs shown to be implicated. We have recently performed a comparative sRNA profiling via deep-sequencing of P. aeruginosa PAO1 and PA14 strains [2] which share the same host range but differ in pathogenicity.
We now aim to unravel virulence-relevant sRNA-based regulatory systems throughout the panel of novel sRNAs that we have identified. In this study, we have collected evidences for the involvement of the conserved sRNA SPA0122 in the regulation of two typical P. aeruginosa virulence traits: swimming motility and production of pyocyanin, a secreted toxic secondary metabolite. In addition, we suggest that SPA0122 positively regulates the expression of i) a key enzyme providing sugar precursors for the synthesis of exopolysaccarides, one of the biofilm matrix components, and ii) a protein involved in antibiotic susceptibility. Finally, we have evidences that SPA0122 is responsive to infection-relevant host stimuli such as oxygen availability and shift from room to body temperature.
In conclusion, our results indicate that SPA0122, once receiving inputs from host sensing/signaling pathways, plays a role as global co-mediator of complex virulence regulatory sub-networks.
1. Balasubramanian D, Schneper L, Kumari H & Mathee K (2013) A dynamic and intricate regulatory network determines Pseudomonas aeruginosa virulence. Nucleic Acids Res, 41:1-20.
2. Ferrara S, Brugnoli M, De Bonis A, Righetti F, Delvillani F, Dehò G, Horner D, Briani F & Bertoni G (2012) Comparative Profiling of Pseudomonas aeruginosa Strains Reveals Differential Expression of Novel Unique and Conserved Small RNAs. PLoS One, 7:e36553
The novel small RNA SPA0084 has pleiotropic effects on virulence traits linked to quorum sensing in Pseudomonas aeruginosa
No full textPseudomonas aeruginosa is an important opportunistic pathogen in immune-compromised and cystic fibrosis patients, responsible for acute and chronic infections. It produces a large arsenal of virulence factors and is endowed with enhanced capability of biofilm formation. The expression of these virulence traits is fine-tuned by a dynamic and intricate regulatory network [1], in which quorum sensing (QS) has central role. In bacterial pathogens, small RNAs (sRNAs) have been recognized as key elements of the coordinate expression of the virulence factors underlying the interaction with host [2].
In this work, we suggest that the novel sRNA SPA0084 of P. aeruginosa [3] is linked to the las QS network [4]. Our results show that SPA0084 is up-regulated in mutants of lasR and lasI, two key QS genes for the LasI synthase of 3-oxo-C12-homoserine lactone (3OC12HSL), and for LasR receptor of 3OC12HSL, respectively. SPA0084 is also responsive to infection-relevant cues that P. aeruginosa can experience in mammalian hosts like limited iron availability, temperature shifts from environmental to body temperature and reduced oxygen conditions. Moreover, we show that, following overexpression, SPA0084 has pleiotropic effects on virulence traits linked to QS such as motility, pyoverdine, pyocyanin, protease, emolytic activity as long as biofilm formation.
Finally, we predicted in silico and validated both in vitro and in vivo by using a GFP-based reporter system that SPA0084 can target the mRNAs of lasR and lasI. Therefore, SPA0084 could influence QS-regulated virulence traits via the modulation of lasR and lasI genes.
1. Balasubramanian et al. (2013) A dynamic and intricate regulatory network determines Pseudomonas aeruginosa virulence. Nucleic Acids Res, 41:1-20.
2. Caldelari et al. (2013) RNA-mediated regulation in pathogenic bacteria. Cold Spring Harb Perspect Med, 2013;3:a010298.
3. Ferrara et al. (2012) Comparative profiling of Pseudomonas aeruginosa strains reveals differential expression of novel unique and conserved small RNAs. PLoS One, 7:e36553.
4. Rutherford ST, Bassler BL (2012) Bacterial quorum sensing: its role in virulence and possibilities for its control. Cold Spring Harb Perspect Med, 2012;2:a012427
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
A Revision of the Biginelli Reaction Under Solid Acid Catalysis. Solvent-free Synthesis of Dihydropyrimidine over Montmorillonite KSF
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