Metal-metabolomics of microalga Chlorella sorokiniana growing in selenium- and iodine-enriched media

Abstract

The microalga Chlorella sorokiniana has been used to accumulate selenium and iodine from culture media enriched with these elements as a first stage in the production of supplemented foods. The microalgal colony was grown in a conventional culture medium containing iodine (KI) at concentrations in the range of 150–4000 μg mL−1. Similar experiments were performed with selenium (SeO42−) at concentrations in the range of 20–500 μg mL−1. The concentration of iodine and selenium in the culture medium was analytically monitored daily and the viability of the colony was checked by biomass concentration measurement and by evaluation of the total content of chlorophyll and carotenoids. In addition, photosynthetic activity and the number of cells were also monitored. Iodine accumulation in the algal biomass increased rapidly with time and reached a steady state after 4 h of exposure. With Se exposure the colony viability decreased, although the culture grew well with concentrations of the element of 50 μg mL−1 in the culture medium; this experiment produced Se-enrichment in the alga (3 μg g−1) within 100 h. Sequential extraction of an algal pellet was performed in order to separate Se compounds according to their affinity with the following solvents: hot water to recover low molecular mass Se species, enzymatic extraction with driselase for species associated with the cell wall, sodium dodecyl sulphate (SDS) for water insoluble selenoproteins and, finally, enzymolysis with lipase and pronase that release and fragment residual selenoproteinsproducing compounds with low molecular mass. Size-exclusion chromatography (SEC) coupled with an ICP-MS detector showed the preponderance of Se-containing molecules with low molecular mass, possibly seleno-amino acids. Only a peak of low intensity located at 10 min was observed in the SDS extract that could be associated with a protein with molecular mass of 67 kDa. Finally, analysis of the aqueous extract of alga by reverse-phase chromatography with inductively-coupled plasma mass-spectrometry (RPC-ICP-MS) detection revealed the presence of selenocysteine (SeCys2), selenomethylselenocysteine (SeMetSeCys), selenomethionine (SeMet), and Se(VI), particularly the last two species.

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

“…As can be seen in Figure 8 Chlorella sorokiniana accumulated about 60 mg·kg −1 of SeMet in first 24 h of cultivation and doubled this value after 48 h, and increased moderately (approximately 5% daily), while intracellular Se(+VI) concentration gradually decreased, due to its transformation to SeMet and intermediates (SeCys) 2 and SeMeSeCys [ 48 ]. At the end of the experiment total accumulation of SeMet was 140 mg·kg −1 , while intracellular Se(+VI) concentration decreased by 50% from the initial value.…”

“…A solution containing Li, Y, Tl, and Ce (1 μ g·L −1 each) prepared in the mobile phase was used to tune the ICP-MS for sensitivity, resolution, percentage of oxides, and doubly charged ions. The chromatographic separation was performed on the basis of previously described instrumental coupling [ 47 , 48 ].…”

Exploring the Chemical Space of Macro- and Micro-Algae Using Comparative Metabolomics

“…Metabolomics, using liquid chromatography-mass spectrometry (LC-MS) or tandem mass spectrometry (LC-MS/MS) data, has been used for this purpose. This approach has been used to study the accumulation of starch in Chlamydomonas reinhardtii in response to changes in circadian rhythm [ 14 ], and the uptake of the metals selenium and iodine by cultures of Chlorella sorokiniana [ 15 ]. In order to gain an insight into the similarities and differences between crude metabolite extracts from the culture of different species, supervised statistical analyses, such as partial least squares discriminant analysis (PLS-DA), have been deployed [ 16 ].…”

Development of a Constructed Wetland Water Treatment System for Selenium Removal: Incorporation of an Algal Treatment Component

“…17 and Chlorella sorokiniana. 36 Nutrient Interactions. In experiment 2, Scenedesmus obliquus was supplied with 40 μM Se (3160 μg Se/L) in the absence (i.e., deionized water) and presence of nutrients (1/5 Hoagland's solution).…”