Characterization of Tyrosine Decarboxylase (tyrDC) Activity in Genus Enterococcus

The presence of biogenic amines in foods and the risks associated to their consumption (especially considered the increase of susceptible consumers) are well known since long time, but systematic studies about their production have been carried out only in the last decades. Fermented foods, in particular, are often characterized by the presence of relevant concentrations of biogenic amines due to the activity of the microbiota responsible for the secondary fermentation. Within this microbiota, enterococci play a controversial role, in fact they contribute to the definition of typical organoleptic profile of some fermented foods, but at the same time they are characterized by different virulence factors and by the ability to produce high concentrations of biogenic amines, in particular tyramine and 2-phenylethylamine. In this perspective, this PhD thesis represents a contribution for a deeper insight of factors, biological mechanisms and genetic characteristics that influence the activity of tyrosine decarboxylase enzymes in strains belonging to the species Enterococcus faecalis, Enterococcus faecium and Enterococcus mundtii. The results of these studies indicated that qualitatively and quantitatively kinetics of tyramine and 2-phenylethylamine production can vary within species, but also strains. These differences can be related to the effects of the specific composition of substrates, the technological variables (temperature, NaCl concentrations, pH) and the specific genetic characteristics of tyrosine decarboxylase cluster and its transcription. Moreover this thesis highlighted the differences in the responses to environmental factors of a pure enzyme respect microbial cells, to better understand the relationships between decarboxylating activity and the integrity of microbial cells. The data obtained indicating that the decarboxylation activity has to be viewed in the light of the overall cell metabolism. Finally, the use of bioprotective cultures producing bacteriocins as antagonists against biogenic amine producing microorganisms has been exploited to reduce the risks of biogenic amine accumulation in fermented foods

Tyrosine decarboxylase activity of Enterococcus mundtii: new insights into phenotypic and genetic aspects

Few information is available about the tyraminogenic potential of the species Enterococcus mundtii. In this study, two plant-derived strains of E. mundtii were selected and investigated to better understand the phenotypic behaviour and the genetic mechanisms involved in tyramine accumulation. Both the strains accumulated tyramine from the beginning of exponential phase of growth, independently on the addition of tyrosine to the medium. The strains accumulated also 2-phenylethylamine, although with lower efficiency and in greater extent when tyrosine was not added. Accordingly, the tyrosine decarboxylase (tyrDC) gene expression level increased during the exponential phase with tyrosine added, while it remained constant and high without precursor. The genetic organization as well as sequence identity levels of tyrDC and tyrosine permease (tyrP) genes indicated a correlation with those of phylogenetically closer enterococcal species, such as E. faecium, E. hirae and E. durans; however, the gene Na+/H+ antiporter (nhaC) that usually follow tyrP is missing. In addition, BLAST analysis revealed the presence of additional genes encoding for decarboxylase and permease in the genome of several E. mundtii strains. It is speculated the occurrence of a duplication event and the acquisition of different specificity for these enzymes that deserves further investigations

The Relationship among Tyrosine Decarboxylase and Agmatine Deiminase Pathways in Enterococcus faecalis

Enterococci are considered mainly responsible for the undesirable accumulation of the biogenic amines tyramine and putrescine in cheeses. The biosynthesis of tyramine and putrescine has been described as a species trait in Enterococcus faecalis. Tyramine is formed by the decarboxylation of the amino acid tyrosine, by the tyrosine decarboxylase (TDC) route encoded in the tdc cluster. Putrescine is formed from agmatine by the agmatine deiminase (AGDI) pathway encoded in the agdi cluster. These biosynthesis routes have been independently studied, tyrosine and agmatine transcriptionally regulate the tdc and agdi clusters. The objective of the present work is to study the possible coregulation among TDC and AGDI pathways in E. faecalis. In the presence of agmatine, a positive correlation between putrescine biosynthesis and the tyrosine concentration was found. Transcriptome studies showed that tyrosine induces the transcription of putrescine biosynthesis genes and up-regulates pathways involved in cell growth. The tyrosine modulation over AGDI route was not observed in the mutant 1 tdc strain. Fluorescence analyses using gfp as reporter protein revealed PaguB (the promoter of agdi catabolic genes) was induced by tyrosine in the wild-type but not in the mutant strain, confirming that tdc cluster was involved in the tyrosine induction of putrescine biosynthesis. This study also suggests that AguR (the transcriptional regulator of agdi) was implicated in interaction among the two clusters

Highly Sensitive Fluorescence Probe Based on Functional SBA-15 for Selective Detection of Hg2+

An inorganic–organic hybrid fluorescence chemosensor (DA/SBA-15) was prepared by covalent immobilization of a dansylamide derivative into the channels of mesoporous silica material SBA-15 via (3-aminopropyl)triethoxysilane (APTES) groups. The primary hexagonally ordered mesoporous structure of SBA-15 was preserved after the grafting procedure. Fluorescence characterization shows that the obtained inorganic–organic hybrid composite is highly selective and sensitive to Hg2+ detection, suggesting the possibility for real-time qualitative or quantitative detection of Hg2+ and the convenience for potential application in toxicology and environmental science

Kinematics and Age of Syn-Intrusive Detachment Faulting in the Southern Alps: Evidence for Early Permian Crustal Extension and Implications for the Pangea A Versus B Controversy

Permian basin formation and magmatism in the Southern Alps of Italy have been interpreted as expressions of a WSW‐ENE‐trending, dextral megashear zone transforming Early Permian Pangea B into Late Permian Pangea A between ~285 and 265 Ma. In an alternative model, basin formation and magmatism resulted from N‐S crustal extension. To characterize Permian tectonics, we studied the Grassi Detachment Fault, a low‐angle extensional fault in the central Southern Alps. The footwall forms a metamorphic core complex affected by upward‐increasing, top‐to‐the‐southeast mylonitization. Two granitoid intrusions occur in the core complex, the synmylonitic Val Biandino Quartz Diorite and the postmylonitic Valle San Biagio Granite. U‐Pb zircon dating yielded crystallization ages of 289.1 ± 4.5 Ma for the former and 286.8 ± 4.9 Ma for the latter. Consequently, detachment‐related mylonitic shearing took place during the Early Permian and ended at ~288 Ma, but kinematically coherent brittle faulting continued. Considering 30° anticlockwise rotation of the Southern Alps since Early Permian, the extension direction of the Grassi Detachment Fault was originally ~N‐S. Even though a dextral continental wrench system has long been regarded as a viable model at regional scale, the local kinematic evidence is inconsistent with this and, rather, supports N‐S extensional tectonics. Based on a compilation of >200 U‐Pb zircon ages, we discuss the evolution and tectonic framework of Late Carboniferous to Permian magmatism in the Alps

In Cima alle Maddalene, Dentro la Terra

Manifestazione di divulgazione-scientifica che si \ue8 tenuta il 17 settembre 2011 presso l\u2019auditorium comunale di Rumo (Trento). La manifestazione, rivolta verso tutti i cittadini e appassionati della natura di Rumo e dintorni ha avuto un triplice scopo: (1) avvicinare i cittadini di Rumo e della Provincia Autonoma di Trento alle attivit\ue0 di ricerca del Dipartimento di Scienze della Terra e Geologico-Ambientali; (2) mostrare i risultati conseguiti dal Dipartimento in questa zona delle Alpi (la Catena delle Maddalene), dove affiorano rocce uniche nel panorama geologico italiano, le cosiddette peridotiti a granato; (3) lanciare l'iniziativa "Centro Studi Geologici Lauro Morten" (dal nome di un docente di petrologia dell'Universit\ue0 di Bologna