Selenium (Se) is an element with many commercial applications as well as an essential micronutrient. Dietary Se has antioxidant properties and it is known to play a role in cancer prevention. However, the general population often suffers from Se deficiency. Green algae, such as Chlorella vulgaris, cultivated in Se-enriched environment may be used as a food supplement to provide adequate levels of Se. We used Raman microspectroscopy (RS) for fast, reliable, and non-destructive measurement of Se concentration in living algal cells. We employed inductively coupled plasma-mass spectrometry as a reference method to RS and we found a substantial correlation between the Raman signal intensity at 252 cm-1 and total Se concentration in the studied cells. We used RS to assess the uptake of Se by living and inactivated algae and demonstrated the necessity of active cellular transport for Se accumulation. Additionally, we observed the intracellular Se being transformed into an insoluble elemental form, which we further supported by the energy-dispersive X-ray spectroscopy imaging.

• Klíčová slova
• Chlorella vulgaris, EDX, ICP-MS, Raman spectroscopy, algae, bioaccumulation, selenium,
• MeSH
• bioakumulace MeSH
• chemické látky znečišťující vodu analýza   metabolismus   MeSH
• Chlorella vulgaris chemie   metabolismus   MeSH
• Ramanova spektroskopie * MeSH
• selen analýza   metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• chemické látky znečišťující vodu MeSH
• selen MeSH

Microalgae are able to metabolize inorganic selenium (Se) to organic forms (e.g. Se-proteins); nevertheless at certain Se concentration culture growth is inhibited. The aim of this work was to confirm the hypothesis that the limit of Se tolerance in Chlorella cultures is related to photosynthetic performance, i.e. depends on light intensity. We studied the relation between the dose and irradiance to find the range of Se tolerance in laboratory and outdoor cultures. At low irradiance (250 µmol photons m-2 s-1), the daily dose of Se below 8.5 mg per g of biomass (<20 µM) partially stimulated the photosynthetic activity (relative electron transport rate) and growth of Chlorella cultures (biomass density of ~1.5 g DW L-1) compared to the control (no Se added). It was accompanied by substantial Se incorporation to microalgae biomass (~0.5 mg Se g-1 DW). When the Se daily dose and level of irradiance were doubled (16 mg Se g-1 DW; 500 µmol photons m-2 s-1), the photosynthetic activity and growth were stimulated for several days and ample incorporation of Se to biomass (7.1 mg g-1 DW) was observed. Yet, the same Se daily dose under increased irradiance (750 µmol photons m-2 s-1) caused the synergistic effect manifested by significant inhibition of photosynthesis, growth and lowered Se incorporation to biomass. In the present experiments Chl fluorescence techniques were used to monitor photosynthetic activity for determination of optimal Se doses in order to achieve efficient incorporation without substantial inhibition of microalgae growth when producing Se-enriched biomass.

• Klíčová slova
• Chlorella, Chlorophyll fluorescence, Growth, Irradiance intensity, Photosynthesis, Selenium incorporation,
• Publikační typ
• časopisecké články MeSH

The aim of this work was to study the effect of Se(+VI) on viability, cell morphology, and selenomethionine accumulation of the green alga Chlorella sorokiniana grown in batch cultures. Culture exposed to sublethal Se concentrations of 40 mg · L(-1) (212 μM) decreased growth rates for about 25% compared to control. A selenate EC50 value of 45 mg · L(-1) (238.2 μM) was determined. Results showed that chlorophyll and carotenoids contents were not affected by Se exposure, while oxygen evolution decreased by half. Ultrastructural studies revealed granular stroma, fingerprint-like appearance of thylakoids which did not compromise cell activity. Unlike control cultures, SDS PAGE electrophoresis of crude extracts from selenate-exposed cell cultures revealed appearance of a protein band identified as 53 kDa Rubisco large subunit of Chlorella sorokiniana, suggesting that selenate affects expression of the corresponding chloroplast gene as this subunit is encoded in the chloroplast DNA. Results revealed that the microalga was able to accumulate up to 140 mg · kg(-1) of SeMet in 120 h of cultivation. This paper shows that Chlorella sorokiniana biomass can be enriched in the high value aminoacid SeMet in batch cultures, while keeping photochemical viability and carbon dioxide fixation activity intact, if exposed to suitable sublethal concentrations of Se.

• MeSH
• bioreaktory mikrobiologie   MeSH
• Chlorella cytologie   účinky léků   fyziologie   MeSH
• kyselina selenová aplikace a dávkování   MeSH
• proliferace buněk účinky léků   fyziologie   MeSH
• selenomethionin izolace a purifikace   metabolismus   MeSH
• techniky vsádkové kultivace metody   MeSH
• velikost buňky účinky léků   MeSH
• viabilita buněk účinky léků   fyziologie   MeSH
• vztah mezi dávkou a účinkem léčiva MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• kyselina selenová MeSH
• selenomethionin MeSH