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Tesi etd-09222017-225911

Thesis type
Tesi di laurea magistrale
email address
Metal nanoparticles toxicity in marine photosynthetic organisms assessed through biophysical phenotyping: a first approach for stress evaluation
Corso di studi
relatore Prof. Pretti, Carlo
correlatore Prof. Scarpato, Roberto
correlatore Prof. Coppedè, Fabio
Parole chiave
  • Pulse Modulated Amplitude
  • Copper
  • Nanoparticles
  • Pheodactylum Tricornutum
  • Heavy Metal
Data inizio appello
Data di rilascio
Riassunto analitico
Heavy metal pollution poses a serious threat to environment. Wrong management of anthropogenic heavy metal waste can lead to serious alterations in organisms’ life as well as in whole ecosystems.
A big part of metal pollution affects marine life directly or altering the equilibrium of metals as trace nutrients, with potential toxic effects in concentrations higher than their own optimum.
The large increase of metal ENPs (Engineered Nano Particles) in the environment due to their large employ in nano-sized materials production, has risen concerns about their potential role as new contaminant in marine environment. Depending on ENPs nature, size and behaviour in seawater, their toxic effects cannot be included in those of their dissolved metal counterpart.
Given the lack of knowledge of clear effects of MeENP in marine environment, it is important to highlight their toxic profiles on marine organisms, being aquatic environments the ultimate sink for every contaminant.
In the present work we focused on Cu, an essential metal for marine organisms that could easily become toxic where and when its concentration increases to critical levels. The aim of this study is to compare the effects of Cu nanoparticles with its dissolved counterpart and how they can differently affect marine primary producers. The diatom Pheodactylum tricornutum was used as model organism due to its wide employment in various studies and for its global distribution.
Monoclonal cultures of diatom P. tricornutum were monitored for 5 days and exposed to three increasing concentrations of dissolved and ENP metal along exponential phase of growth. Pulse modulated Amplitude (PAM) fluorometry was performed during all the days of treatment, in order to assess the toxic effects of metals on growth and photosynthetic efficiency. At the end of the exponential phase, pellets from the cultures were used to determine effects on pigments, fatty acid composition and oxidative stress.
Photosynthetic processes and whole primary productivity are highly sensitive to metal pollution, showing different responses in dissolved or in nanoparticle form of the same metal. The uptake of different forms of a metal can also affect the stability of photosynthetic pigments (e.g. CuChl formation under high Cu exposure), as well as membranes fatty acid composition (minor production of Eicosapentaenoic acid –EPA-) and antioxidant processes.
The application of Pulse Modulated Amplitude (PAM) Fluorescence has been found to be useful to detect and analyse the complex photosynthetic processes, under different culture conditions, highlighting alterations in various parameters along the energy transduction pathway with a high- throughput non-invasive way. PAM phenotyping performed in metal-treated P. tricornutum cells points out to a differential effect of Cu and Zn in their dissolved or nanoparticle forms in the photosynthetic energy transduction pathways.
Gas Chromatography was used to draw fatty acid profiles of the samples, focusing on the percentage of EPA produced under different conditions of stress.
Initial analysis on pigments data on Cu clearly showed a higher CuChl substitution grade in cultures treated with copper nanoparticles than in those treated with its dissolved form. A preliminary analysis of fatty acid composition showed a gradual reduction of the major membrane polyunsaturated fatty acid EPA with increasing concentration of Cu.
Nevertheless, deeper analysis still needs to be done to support chronic exposure and to obtain an overall and more general sign of stress caused by emerging contaminants.