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 algaChlorella sorokinianagrown 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 EC50value 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 ofChlorella 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−1of SeMet in 120 h of cultivation. This paper shows thatChlorella sorokinianabiomass 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.