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- Photosynthetic pigment laser-induced fluorescence indicators for the detection of changes associated with trace element stress in the diatom model species Phaeodactylum tricornutumPublication . Cabrita, Maria Teresa; Gameiro, C.; Utkin, Andrei B.; Duarte, Bernardo; Caçador, Isabel; Cartaxana, PauloThis work reports changes on cell number, growth rate, trace element content, chlorophyll a (Chl a) and carotenoid concentrations, and laser-induced fluorescence (LIF) spectra of Phaeodactylum tricornutum exposed to Co, Ni, Cu, Zn, Cd, Hg, Pb, and a mixture of all elements combined (Mix). The total levels of trace elements associated with the cells were significantly higher in the exposed than in control ones. Concomitantly, specific cell growth was significantly lower in exposed P. tricornutum, suggesting that trace elements affected the microalgae physiology. The LIF emission spectra showed two typical emission bands in red (683-698 nm) and far-red (725-730 nm) regions. Deviations in LIF spectra and changes in F685/F735 ratio were investigated as indicators of trace element-induced changes. Fluorescence intensity emitted by exposed microalgae decreased in far-red region when compared to control cells, suggesting Chl a damage and impairment of pigment biosynthesis pathways by trace elements, confirmed by Chl a and carotenoid concentration decrease. Significant increase in F685/F735 ratio was detected for all elements except Zn and more accentuated for Co, Hg, and Mix. Significant deviations in wavelength emission maxima in red region were also more significant (between 8 and 13 nm) for Co, Hg, and Mix. Growth changes agreed with deviations in LIF spectra and F685/F735 ratio, supporting their applicability as indicators. This study clearly shows F685/F735 ratio and the deviations in wavelength emission maxima as adequate trace element stress indicators and P. tricornutum as a promising biomonitor model species. LIF-based techniques can be used as time-saving, highly sensitive, and effective alternative tool for the detection of trace element stress, with potential for remote sensing and trace element contamination screening in marine coastal areas.
- Heat wave impacts on the model diatom Phaeodactylum tricornutum: Searching for photochemical and fatty acid biomarkers of thermal stressPublication . Feijão, Eduardo; Gameiro, C.; Franzitta, Marco; Duarte, Bernardo; Caçador, Isabel; Cabrita, Maria Teresa; Matos, Ana RitaGlobal warming is increasing the frequency and intensity of extreme thermal events, with inevitable consequences for marine ecosystems and organisms. Phytoplankton is at the base of marine food webs and diatoms are major contributors to global primary production. Therefore, environmental changes, such as heat, influencing growth, physiology and biochemical composition of diatoms, impact other organisms at higher trophic levels. The model diatom Phaeodactylum tricornutum, particularly rich in the long chain omega-3 eicosapentaenoic acid (EPA), and able to accumulate substantial amounts of storage lipids, has recently been the object of numerous works, regarding fundamental aspects of lipid metabolism and exploring its biotechnological potential for biodiesel and aquaculture purposes. The aim of this study was to use P. tricornutum, growing under controlled conditions, to examine the effects of a heat wave, in order to identify heat stress biomarkers. The photosynthetic and respiratory metabolism was investigated by Chlorophyll a fluorescence and by O2 evolution and discussed in connection with changes observed in the composition of photosynthetic pigments and fatty acids. Phaeodactylum tricornutum cells exposed to 26 °C displayed lower photosynthetic O2 production, but similar respiratory rate, comparing to cells at control temperature (18 °C), which is likely related to the biomass decrease observed under heat stress. Heat wave exposed cells also showed a less efficient PSII, higher energy dissipation and higher chlorophyll a and fucoxanthin concentrations, suggesting a heat-induced amplification of the light energy absorption capacity. Heat wave exposed cells showed lower relative EPA contents and double bond indexes, whereas the parameter inversely related to nutritional value, omega 6/omega 3 ratio, increased. Moreover, the analysis of the fatty acid profiles also suggested that heat exposure negatively impacted thylakoid lipids, in agreement with the decrease observed in photosynthesis. Results obtained highlight the negative impact of heat waves on diatom photosynthesis and nutritional value, as well as on their capacity to oxygenate ocean water. Furthermore, physiological parameters as well as fatty acids and photosynthetic pigments signatures, were identified, that could represent expedite biomarkers of thermal stress in future studies.
- Photochemical features and trace element substituted chlorophylls as early detection biomarkers of metal exposure in the model diatom Phaeodactylum tricornutumPublication . Cabrita, Maria Teresa; Duarte, Bernardo; Gameiro, C.; Godinho, Rita M.; Caçador, IsabelEstablishing marine species equipped with efficient biomarkers of trace element stress is a major requirement for the assessment of trace element contamination in marine ecosystems. This study investigates PS II overall activity and efficiency during light harvesting, electron transport chain (ETC) behaviour, OJIP-transient light curves, and pigment profiles, in the model marine diatom species Phaeodactylum tricornutum exposed to Cr, Co, Ni, Cu, Zn, Cd, Hg, Pb and to a mixture of all elements combined (Mix). OJIP-test parameters and trace element substituted chlorophylls were investigated as potential biomarkers of stress induced by trace elements. Hg-exposed cells showed a shift in balance towards PS I activity, promoted by increase in the electron transport from PQH2 to the reduction of PS I end electron acceptors. Other elements had more limited effects, mostly affecting energy dissipation and pigment levels to various degrees. Decoupling of PS II antennae connectivity was found in Co exposed cells. Chromium induced negative effects on PS I, but had no influence at the Oxygen Evolving Complexes (OECs) level. Copper caused a shift in the equilibrium between PS towards the PS I by reducing the PS II efficiency. Cadmium induced damage in OECs of the PS II donor side, but had no effect on the energy transduction pathway, maintaining energy processing efficiency. Lead had no significant effect on the energy transduction pathway, but produced changes at pigment level, leading to an increase in the chlorophyll and diadinoxanthin. In contrast, Ni had a beneficial role in P. tricornutum photochemistry, leading to increased number of available RC and oxidized quinone pool size, possibly because concentrations used were not able to induce severe cell damage. Copper, Cd and Zn led to substitution of Mg in chlorophyll a molecules, with the formation of less efficient CuChl a, CdChl a and ZnChl a. The biomarkers used evidenced the damaging effect of Co, Cu, Cr, Pb, Hg and all trace elements combined (Mix), pointing to Hg as the most harmful element. These physiological changes highlight P. tricornutum as a promising sentinel species for trace element contamination and the proposed photochemical features suitable as an efficient battery of biomarkers for trace element stress early detection in marine systems.