4,548 research outputs found
A possibile role of nirK in Rhizobium sullae HCNT1.
No full textIn response to a number of environmental stresses many bacterial species, including Vibrio
vulnificus, Sinorhizobium meliloti, Micrococcus luteus, Escherichia coli and Helicobacter pylori,
enter the viable-but-not-culturable (VBNC) status (McDougald et al., 1998). In this metabolic state
they lose their ability to grow on media that usually sustain them and undergo such physiological
and morphological changes as increased resistance to several physic and chemical factors, and
changes in protein and lipid content. The recent increasing use of specific fluorescent dyes such as
Syto 9, CTC (5-cyano-2,3-di-4-tolyl-tetrazolium chloride), AO (Acridine Orange), propidium
iodide, made possible a proper identification of viability and the metabolic state of microbes
(Basaglia et al. 1997).
Sinorhizobium meliloti 41, a rhizobium nodulating Medicago sativa, enters VBNC status in
liquid microcosms when O2 is depleted from the atmosphere of the incubation mixture (Toffanin et
al., 2000; Casella et al. 2001). Plasmid-borne, firefly-derived, luciferase gene (luc) was inserted and
stably inherited in Sinorhizobium meliloti 41 (pRP4-luc) as a reporter gene. The strain obtained, S.
meliloti 41 pRP4-luc and its parental strain, served as a model system for VBNC experiments both
in vitro and in soil samples.
Rhizobium sullae, formerly Rhizobium ’hedysari’, is a nitrogen fixing bacterium that induces
symbiotic nodule formation on the legume Hedysarum coronarium (Squartini et al., 2002). Strain
HCNT1, expressing a copper-containing nitrite reductase encoded by nirK, which is closely related
to nitrite reductases in true denitrifiers, enters the same VBNC status when oxygen is limiting, but
only when nitrite is present and converted to NO. Since HCNT1 cannot grow as a denitrifier and
inactivation of nirK only resulted in the loss of NO production (Toffanin et al, 1996), the hypothesis
that expression of nirK may induce the VBNC status has been investigated.
Therefore, a comparison between the two systems, S. meliloti and R. sullae, is presented in order
to verify the possible connection of nirK with the VBNC status.
McDougald D. et al. 1998. FEMS Microbiology Ecology 25: 1-9
Basaglia M. et al. 1997. In: The biotechnology and ecological interactions of microbial inoculants".
Granada, Spain. pp. 19-20
Toffanin A. et al. 2000. Biol. Fertil. Soils. 31 (6): 484-488
Casella S. et al. 2001. ISME-9, Amsterdam (The Netherlands), p. 191
Squartini A. et al. 2002. Int. J. Syst. Evol. Microbiol. 52: 1267-1276
Toffanin A. et al. 1996. Appl. Environ. Microbiol. 62 (11): 4019-402
Correction: The reaction of acetonitrile with hydrogen peroxide in alkaline medium: a DFT mechanistic study of green production of amides
No full textCorrection for 'The reaction of acetonitrile with hydrogen peroxide in alkaline medium: a DFT mechanistic study of green production of amides' by Girolamo Casella et al., Phys. Chem. Chem. Phys., 2023, https://doi.org/10.1039/d3cp02024j
AniA, a regulatory protein involved in polymer accumulation in Ensifer meliloti
No full textBacterial biosynthesis of different polymers depends upon the genetic traits of the strain in use and by the culture conditions adopted. Although the separate production of exopolysaccharides (EPS) or poly-3-hydroxybutyrate [P(3HB)] is well documented, much less attention has been paid to the relationships between the synthesis of these two major compounds produced by bacteria. The biosynthetic pathways of these polymers are not directly linked, but they can be produced at the same time in some microorganisms. In rhizobia the general conditions governing the biosynthetic pathways (the nature and availability of carbon and nitrogen sources, the oxygenation, the energetic and redox states of cells, the environmental constraints, etc.) seem to be the same. Since the extent of EPS and P(3HB) production implies a significant energetic cost, a sensitive regulatory mechanism is required. A control of the synthesis and degradation of P(3HB) in bacteroids is important to maintain an effective symbiosis. Therefore, a well-regulated P(3HB) cycle results as a key factor for an optimal use of the available energy and for a balanced distribution of the carbon resources. Regulation of carbon flux into P(3HB) production occurs at multiple levels, and the comprehension of this regulation is essential for understanding the physiological functions of P(3HB) and possibly for applying this knowledge to industrial production of polyesters. AniA, a putative regulatory protein previously described (Povolo and Casella, 2000), and identified in the polyhydroxyalkanoates locus in Ensifer meliloti (Tombolini et al. , 1995), was found to be involved in carbon/energy regulation under normal growth conditions. The occurrence of AniA orthologs (described in some cases as PhaR) and organization of the respective genes were described in detail in many different bacteria (Pötter et al., 2005).
The present work gives a better inside of the role of the carbon flux regulator (aniA) in E. meliloti 41. Previous studies on other bacterial species indicated that the impaired synthesis of one polymer causes other reserve materials to be turned over (Breuer and Babel, 1999). A strain carrying a lacZ transcriptional fusion inside the aniA gene was constructed from E. meliloti 41 and from the mutant strain E. meliloti 41003 unable to accumulate polyhydroxyalkanoates (Povolo and Casella, 2008). E. meliloti 41003 accumulates also less exopolysaccharides as compared to the wild-type strain 41 (Povolo and Casella, 2008). The transcription of aniA-lacZ fusions was studied in the wild-type and in the phaC-mutant backgrounds under different conditions. We also showed that an EPS negative mutant of E. meliloti 2011 (strain H3a) could accumulate more P(3HB) than the wild-type strain 2011.
All together these results indicate a clear correlation between P(3HB) and EPS biosynthesis. On the other hand, an aniA-Km mutation was transferred to different E. meliloti strains carrying exp-lacZ and exo-lacZ fusions. Phenotypic analysis of these double mutants showed a change from rough colonies of the single mutants to mucoid colonies in the double mutants (strains exoY-lacZ/aniA-, exoL-lacZ/aniA- and exoP-lacZ/aniA-) indicating an effect of aniA on EPS production
Sub-second variability in black-hole X-ray binary jets
No full textIn the last 10 years, multiwavelength fast variability studies of low-mass X-ray binaries have shown a dramatic development. A key discovery was the detection of O-IR sub-second fluctuations in two black-hole transients, lagging the X-rays by ≈0.1 s. This demonstrated how the fluctuations observed in the inflow could be transferred to the jet, allowing, therefore, also to study in a completely new way the physical processes that take place at the base of the jet. In this article, we review the latest developments of the study of jets with this new approach, focusing on the results obtained with cross-spectral analysis techniques.</p
Dealing with a cluster of large centralized municipal wastewater treatment plants: A case study
No full textThe article deals with a cluster of large centralized municipal wastewater treatment plants (LCMWWTPs) assessing the main economic, energy, environmental and management aspects. With reference to the case study of the Regi Lagni system (Southern Italy), composed of five WWTPs for an overall effective population of 2,235,800 inhabitants the study focused first on the multi-disciplinary characterization of the system investigated and then on potential future upgrading options, identifying the best suitable solution. For the scope, several indicators such as running costs, energy consumptions, Greenhouse Gas Emissions (GHG), waste for landfilling and two scenarios were defined. The first scenario focused on the role of anaerobic digestion while the dewatered sludge was sent to landfill. The second scenario implemented the same operations of the previous one although the construction of a thermal treatment plant for the dewatered sludge was also planned. Results showed how LCMWWTPs could be characterised by low resilience; the upgrading of plants to comply with the increasingly stringent legal limits was difficult, especially where works were carried out to ensure continuity of operation. Multi-criteria analysis allowed the cluster system based on anaerobic digestion to be the best solution from an economic, energy and environmental point of view. © 2018 Institution of Chemical Engineer
Elucidating the cause and effect of NO accumulation in R. sullae Strain HCNT1
No full textRhizobium sullae, formerly Rhizobium ’hedysari’, is a nitrogen fixing bacterium that induces symbiotic nodule formation on the legume Hedysarum coronarium. Some isolates belonging to this species have been shown to encode a copper-containing nitrite reductase, encoded by nirK, which is closely related to nitrite reductases in true denitrifiers. Nitrite reductase reduces nitrite to nitric oxide (NO). Nir activity in the HCNT1 strain is induced under low oxygen and results in accumulation of toxic levels of NO if nitrite is present. Therefore, HCNT1 cannot grow as a denitrifier. Inactivation of nirK resulted in no obvious phenotypic changes other than those linked to the loss of NO production (Toffanin et al, 1996) Strains of the same species that lack Nir (e.g. strain CC1335) can nodulate and fix nitrogen at the same level so the function of Nir in HCNT1 is unclear. Recent investigations showed that strain HCNT1, as well as other bacteria including different species of rhizobia, can enter the so-called VBNC (Viable But Not Culturable) state (Toffanin et al., 2000) when oxygen is limiting and nitrite is converted to NO. Such a metabolic state confers to the cells the ability to withstand stresses, including antibiotic effects or nutrient depletion; when suitable environmental conditions resume, it has been demonstrated that some VBNC bacterial populations can recover their culturability (Casella et al, 2001).
In order to verify the hypothesis that expression of nirK is favourable because it induces the VBNC state, nirK from HCNT1 has been mobilized into CC1335 and the resulting phenotype studied. In related work the occurrence of genes encoding NO reductase in various R. sullae strains has been examined by a PCR-based approach. This was done to determine if the NO accumulation phenotype is due to loss of genes encoding NO reductase
Il dialogo pseudo-platonico Amanti: la polemica contro Isocrate e l’Accademia sotto il magistero di Platone
No full textIn this paper, the author analyses the dialogue Lovers or Rivals. Some scholars argue in favour of Plato’s authorship, while others agree on its inauthenticity. The thesis of its inauthenticity will be defended without reappraising and developing the most prevalent hypothesis, namely that the dialogue was composed in the third century BCE as a pamphlet against the Peripatetic school. In fact, the author advances the hypothesis that the Lovers were written by a disciple of Plato in the fourth century BCE, and that the dialogue clearly attacks Isocrates and, in particular, his conception of philosophy described for example in his Antidosis. The author will argue that the dialogue possesses a protreptic intent and perhaps addresses some of those issues that were most considered by Plato himself: finding a proper definition of philosophy and encouraging philosophers to engage in politics
Minorities and Storable Votes
No full textThe paper studies a simple voting system that has the potential to increase the power of minorities without sacrificing aggregate efficiency. Storable votes grant each voter a stock of votes to spend as desired over a series of binary decisions. By accumulating votes on issues that it deems most important, the minority can win occasionally. But because the majority typically can outvote it, the minority wins only if its strength of preference is high and the majority’s strength of preference is low. The result is that with storable votes, aggregate efficiency either falls little or in fact rises. The theoretical predictions of our model are confirmed by a series of experiments: the frequency of minority victories, the relative payoff of the minority versus the majority, and the aggregate payoffs all match the theory.
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