Effect of Selenate on Viability and Selenomethionine Accumulation ofChlorella sorokinianaGrown in Batch Culture

Abstract

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.

Nutritional Potential and Toxicological Evaluation of Tetraselmis sp. CTP4 Microalgal Biomass Produced in Industrial Photobioreactors

“…Although low amounts of selenium and iodine were detected, it should be noted that both elements were not included in the industrial culture medium used for growth. Therefore, the addition of inorganic sources of both elements in the culture medium used for industrial production might allow improvement of the concentrations obtained in the final biomass product, as previously described for other chlorophytes [50]. Bioaccumulation of selenium has also been observed in Tetraselmis sp.…”

The synergistic effect of Selenium (selenite, –SeO3 2−) dose and irradiance intensity in Chlorella cultures

“…As an example published data for the microalga Chlorella can be taken for comparison. She can tolerate Se concentrations of up to tens of mg L −1 depending on culturing conditions (Pelah and Ephraim 2005 ; Gojkovic et al 2014 ; Sun et al 2014 ). It is important to consider that reported laboratory cultures were mostly grown in flasks in rather diluted suspensions exposed to 50–100 µmol photons m −2 s −1 .…”

“…When culturing in excessive Se concentrations the early response of microalgae culture is significant decrease of photosynthetic activity monitored as oxygen evolution or Chl fluorescence quenching (e.g. Geoffroy et al 2007 ; Gojkovic et al 2014 ; Morlon et al 2005 ).…”

“…In order to select appropriate Se dose in our experiments we have considered the tested concentration range of Se salts in cultivation media that was usually between 0.1 and 80 mg L −1 (1–500 μM) (e.g. Bennett 1988 ; Morlon et al 2005 ; Geoffroy et al 2007 ; Umysová et al 2009 ; Fournier et al 2010 ; Gojkovic et al 2014 , 2015 ).…”

“…Microalgae play a crucial role in Se-metabolism due the uptake and biotransformation, and the subsequent transfer upwards into the food chain. Basically, three mechanisms are associated with Se removal by microalgae: (i) biosorption of Se ions on the cell surface, (ii) intracellular uptake of Se ions, and (iii) chemical transformation of Se ions (Neumann et al 2003 ; Pardo et al 2003 ; Pelah and Ephraim 2005 ; Oh et al 2009 ; Umysová et al 2009 ; Gojkovic et al 2014 , 2015 ). The effects of Se, and its metabolism and bioaccumulation have recently been studied in various groups of microalgae including Spirulina (Li et al 2003 ; Mane et al 2013 ; Pronina et al 2002 ), Scenedesmus (Umysová et al 2009 ), Chlorella (Sun et al 2014 ; Gojkovic et al 2014 ) or Chlamydomonas (Geoffroy et al 2007 ; Morlon et al 2005 ).…”