121 research outputs found
The role of microbial populations in the cycling of iron and manganese from marine aggregates
No full textMarine aggregates play an important role in the cycling of carbon, nutrients and tracemetals. Within aggregates the oxygen depleted by aerobic microbial respiration maynot be replaced rapidly, generating anoxic or suboxic microzones. Reducedcompounds that are unstable in the oxygenated water column have been previouslyfound associated with marine snow. Therefore, in the experiments described in thisthesis, artificial aggregates were made in the laboratory from senescent phytoplanktonmaterial and incubated to investigate the role of the associated microbial populationsto the biogeochemical redox cycling of iron and manganese and to the degradation oforganic matter.The release of dissolved iron from artificial aggregates which did not contain anymeasurable (~10 ?m) anoxic microzones, was demonstrated under dark conditions.The rate of release was controlled by the amount of reducible Fe(III) available, andappears to be limited by the competing oxidation of Fe(II). Moreover highly significantreleases in reduced Mn were detected from aggregates incubated under a constantvelocity shear, although the same aggregates did not affect the dissolution of iron. Apossible reason is likely associated with the higher stability of Mn(II), compared toFe(II) in aerobic environments.Molecular (16S rRNA gene) analyses showed the bacterial communityassociated with artificial aggregates to be similar to that found in natural aggregatesand dominated by (predominantly uncultured) ?- and ?-Proteobacteria, Bacteroidetes,Planctomycetes and Cyanobacteria. It was possible to culture NO3--, Fe(III)- andMn(IV)-reducing bacteria from the artificial aggregates, and marine particles incubatedwith Fe(III) under anaerobic conditions contained a range of ?- and ?-Proteobacteriaknown to respire Fe(III) and in most cases Mn(IV). Moreover several microorganismsbelonging to ?-Proteobacteria were isolated from marine aggregates and strainsaffiliated to the genera Amphritea, Marinobacterium and Marinobacter, weredemonstrated to grow through the reduction of Fe(III), with Marinobacter also capableof respiring Mn(IV). Whilst the precise mechanism of reduction is not clear, it is evidentthat marine aggregates can be a source of Fe(II) and dissolved Mn, in coastal watersand most probably other natural water systems.Fatty acid analyses revealed the prevalence of saturated over unsaturated fattyacids indicating that aggregates were already partially degraded when incubationstarted. Nonetheless, the lipids in the artificial aggregates were rapidly degradedfurther as indicated by a depletion in short chain (<20) saturated andmonounsaturated fatty acids. In contrast, the concentrations of linear and branched,saturated long chain (>20) fatty acids fluctuated, suggesting that some of these lipidscould have been produced in situ by marine microorganisms rather than deriving fromIIhigher plant debris. In addition, a bacterial branched monounsaturated fatty acid (11-methyl-octadecenoic acid), which has not previously been found in marine particleswas present in artificial aggregates. Roseobacter litoralis found among the aggregateattachedbacteria contains 11-methyl-octadecenoic acid, and other bacteria present inartificial aggregates have the potential to produce long-chain saturated andpolyunsaturated fatty acids. Thus, the fatty acid assemblage appears to reflect bothorganic matter degradation, including selective preservation, but also changes in themicrobial assemblage.A range of future studies are suggested to elucidate the mechanisms for Fe(III)and Mn(IV) reduction in aggregates. These include microscale analyses of dissolvedspecies and evaluation of the presence of metal binding ligands associated withaggregates. Moreover it is important to assess the activity of the Fe(III)- and Mn(IV)-reducing bacteria present in aggregates in situ and the production of long chain fattyacids in degrading aggregates
Changes in fatty acid composition in degrading algal aggregates
No full textAggregates derived from senescent phytoplankton populations and associated microbial assemblages were incubated aerobically in the dark to assess the compositional changes in lipids during the degradation of artificial marine snow. The prevalence of saturated over unsaturated fatty acids indicated that aggregates were already degraded when incubation started. Nonetheless, the lipids in the artificial aggregates were quickly further degraded as indicated by a depletion in short-chain (< 20) saturated and monounsaturated fatty acids. In contrast, the concentrations of long-chain (> 20) saturated fatty acids fluctuated, suggesting that some of these lipids could have been produced in situ by marine microorganisms rather than deriving from higher plant debris. In addition, a bacterial branched monounsaturated fatty acid (11-methyloctadecenoic acid), which has not been found previously in marine particles was present in artificial aggregates. Molecular (16S rRNA gene) analyses indicate that the bacterial community attached to aggregates is dominated by (predominantly uncultured) ?-Proteobacteria, ?-Proteobacteria and Planctomycetes. Of these, a Roseobacter sp. which was present in artificial aggregates analysed in a parallel study (Balzano et al. 2009, Aquatic Microbial Ecology 54:291–303), can contain 11-methyloctadecenoic acid, and other bacteria present in artificial aggregates have the potential to produce long-chain saturated fatty acids. Thus, the fatty acid assemblage appears to reflect both organic matter degradation, including selective preservation, but also changes in the microbial assemblage
Pedagogia e politiche sociali in tempi di pandemia da Covid-19. Riflessione sul contributo dell’educazione nelle mutate politiche di welfare
No full text“Dobbiamo far ricorso alle nostre capacità e al nostro senso di responsabilità,
per creare convergenze e collaborazione tra le forze di cui disponiamo
perché operino nella stessa direzione. Anche con osservazioni
critiche, sempre utili, ma senza disperderle in polemiche scomposte o nella
rincorsa a illusori vantaggi di parte, a fronte di un nemico insidioso che
può travolgere tutti”. Con queste parole il Presidente della Repubblica Italiana
Sergio Mattarella, nel suo intervento all’assemblea annuale dell’ANCI,
nel novembre 2020, richiamava a quel principio di responsabilità
personale e sociale che la ricerca pedagogia ha sottolineato in questa fase
di pandemia da Covid-19
A Teaching Kinematics: Augmented Reality and Virtualization in the Observation
No full textIn the paper we report on an ongoing experiment aiming to use broadly principles and methods from virtual reality and augmented reality for didactical purposes, in particular in the filed of Kinematics. Key idea is that of providing the observer, an elem
Author response to: Modelling centralization of pancreatic surgery: some additional considerations
No full textNitrosative stress induces aromatase upregulation in astrocytes primary cultures from fetal sheep brain.
No full textExpression and distribution of P450-aromatase in the ovine hypothalamus at different stages of fetal development
No full textOBJECTIVES:
An important step of sexual differentiation is the conversion of testosterone to estrogen by aromatase leading to masculinization and defeminization of the fetal brain areas crucial for normal sexual behavior and reproduction. Brain sexual differentiation occurs throughout a critical period starting from different prenatal stages depending on the species. Such period goes on from gestation day (GD) 30 to 100GD in the sheep. The fetal sheep brain is reported to aromatize androgens to estrogens at 64GD. The main goal of this work was to evaluate aromatase expression in sheep hypothalami during the whole period of sexual differentiation (35GD, 55GD, 80GD, 115GD) and whether differences may be observed depending on gestational stage and sex.
METHODS:
Sections at the hypothalamic level underwent immunoperoxidase technique employing anti-aromatase and anti-androgen receptor antibodies. Samples from 35GD and 55GD were also processed with in situ hybridization using aromatase cDNA probe. Blot analyses were performed to quantify possible aromatase immunoexpression differences between sexes. For sexing, samples at 35GD and 55GD underwent DNA extraction and SRY amplification.
RESULTS:
Our results revealed aromatase and androgen receptor immunoreactivity along the whole period of sexual differentiation. Both molecules were detected in many brain regions and markedly in the periventricular area. The highest aromatase and androgen receptor amounts were observed at 35GD and 55GD, when aromatase was more abundant in females than in males.
CONCLUSIONS:
In conclusion, the sheep can be included among the species where aromatase is highly expressed in the hypothalamus during the whole period of sexual differentiation
Study on aromatase expression and distribution in male and female hypothalamus at early and middle stage of ovine development
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