The adaptive potential of a survival artist: characterization of the in vitro interactions of Toxoplasma gondii tachyzoites with di-cationic compounds in human fibroblast cell cultures

The impact of di-cationic pentamidine-analogues against Toxoplama gondii (Rh- and Me49-background) was investigated. The 72 h-growth assays showed that the arylimidamide DB750 inhibited the proliferation of tachyzoites of T. gondii Rh and T. gondii Me49 with an IC(50) of 0.11 and 0.13 muM, respectively. Pre-incubation of fibroblast monolayers with 1 muM DB750 for 12 h and subsequent culture in the absence of the drug also resulted in a pronounced inhibiton of parasite proliferation. However, upon 5-6 days of drug exposure, T. gondii tachyzoites adapted to the compound and resumed proliferation up to a concentration of 1.2 muM. Out of a set of 32 di-cationic compounds screened for in vitro activity against T. gondii, the arylimidamide DB745, exhibiting an IC(50) of 0.03 muM and favourable selective toxicity was chosen for further studies. DB745 also inhibited the proliferation of DB750-adapted T. gondii (IC(50)=0.07 muM). In contrast to DB750, DB745 also had a profound negative impact on extracellular non-adapted T. gondii tachyzoites, but not on DB750-adapted T. gondii. Adaptation of T. gondii to DB745 (up to a concentration of 0.46 muM) was much more difficult to achieve and feasible only over a period of 110 days. In cultures infected with DB750-adapted T. gondii seemingly intact parasites could occasionally be detected by TEM. This illustrates the astonishing capacity of T. gondii tachyzoites to adapt to environmental changes, at least under in vitro conditions, and suggests that DB745 could be an interesting drug candidate for further assessments in appropriate in vivo models.

Le conseguenze del pensionamento sulle competenze plurilingui di immigrati italiani in Svizzera

La nostra proposta presenta alcuni aspetti e risultati di un progetto dell'Università di Berna che si occupa delle conseguenze del pensionamento sulle competenze plurilingui di immigrati italiani nella Svizzera tedesca. Rifacendoci a De Bot (2007), che ha definito come “language related major life events” i momenti nella vita rilevanti per mutamenti delle competenze linguistiche, ipotizziamo che il pensionamento possa costituire un punto di svolta nella biografia linguistica di migranti (ma non solo) anche se finora mancano gli studi sull’argomento. Nel caso delle persone prese in considerazione il pensionamento rappresenta un momento fondamentale, quasi paragonabile, per le conseguenze che implica, al momento della migrazione. Se quest'ultima è stata, nella maggior parte dei casi, caratterizzata dalla ricerca di lavoro, la nuova fase della vita dopo il pensionamento comporta mutamenti nelle reti sociali e ha conseguenze anche per l'uso delle lingue. Un punto centrale della ricerca è la domanda di come i migranti affrontino questo momento all’interno della situazione diglossica della Svizzera tedesca, in cui lo svizzero tedesco è stato imparato attraverso il contatto strumentale e accanto ad esso si è mantenuta la lingua d'origine (cfr.Berruto 1991). La metodologia applicata consiste in due fasi: nella prima si utilizzano questionari per ottenere informazioni generali sui dati demografici e sulla situazione sociale, e per elicitare autovalutazioni delle competenze linguistiche. Nella seconda si effettuano interviste semiguidate per ottenere informazioni più approfondite sulla vita e sulle biografie linguistiche. Per ottenere dati relativi alle competenze linguistiche, viene inoltre utilizzato un test di competenza dello svizzero tedesco, sviluppato all’interno del progetto sulla base del SOPI (cfr.Kenyon 2000).

A thermodynamic model for di-trioctahedral chlorite from experimental and natural data in the system MgO-FeO-Al2O3-SiO2-H2O. Applications to P-T sections and geothermometry

We present a new thermodynamic activity-composition model for di-trioctahedral chlorite in the system FeO–MgO–Al2O3–SiO2–H2O that is based on the Holland–Powell internally consistent thermodynamic data set. The model is formulated in terms of four linearly independent end-members, which are amesite, clinochlore, daphnite and sudoite. These account for the most important crystal-chemical substitutions in chlorite, the Fe–Mg, Tschermak and di-trioctahedral substitution. The ideal part of end-member activities is modeled with a mixing-on-site formalism, and non-ideality is described by a macroscopic symmetric (regular) formalism. The symmetric interaction parameters were calibrated using a set of 271 published chlorite analyses for which robust independent temperature estimates are available. In addition, adjustment of the standard state thermodynamic properties of sudoite was required to accurately reproduce experimental brackets involving sudoite. This new model was tested by calculating representative P–T sections for metasediments at low temperatures (<400 °C), in particular sudoite and chlorite bearing metapelites from Crete. Comparison between the calculated mineral assemblages and field data shows that the new model is able to predict the coexistence of chlorite and sudoite at low metamorphic temperatures. The predicted lower limit of the chloritoid stability field is also in better agreement with petrological observations. For practical applications to metamorphic and hydrothermal environments, two new semi-empirical chlorite geothermometers named Chl(1) and Chl(2) were calibrated based on the chlorite + quartz + water equilibrium (2 clinochlore + 3 sudoite = 4 amesite + 4 H2O + 7 quartz). The Chl(1) thermometer requires knowledge of the (Fe3+/ΣFe) ratio in chlorite and predicts correct temperatures for a range of redox conditions. The Chl(2) geothermometer which assumes that all iron in chlorite is ferrous has been applied to partially recrystallized detrital chlorite from the Zone houillère in the French Western Alps.