Bioaccumulation and toxicity of selenium compounds in the green alga Scenedesmus quadricauda

Jiří Doucha,Milada Vítová,Dáša Umysová,Monika Hlavová,Irena Doušková,Jiří Machát,Vilém Zachleder,Mária Čížková,Kateřina Bišová

doi:10.1186/1471-2229-9-58

Abstract

BackgroundSelenium is a trace element performing important biological functions in many organisms including humans. It usually affects organisms in a strictly dosage-dependent manner being essential at low and toxic at higher concentrations. The impact of selenium on mammalian and land plant cells has been quite extensively studied. Information about algal cells is rare despite of the fact that they could produce selenium enriched biomass for biotechnology purposes.ResultsWe studied the impact of selenium compounds on the green chlorococcal alga Scenedesmus quadricauda. Both the dose and chemical forms of Se were critical factors in the cellular response. Se toxicity increased in cultures grown under sulfur deficient conditions. We selected three strains of Scenedesmus quadricauda specifically resistant to high concentrations of inorganic selenium added as selenite (Na2SeO3) – strain SeIV, selenate (Na2SeO4) – strain SeVI or both – strain SeIV+VI. The total amount of Se and selenomethionine in biomass increased with increasing concentration of Se in the culturing media. The selenomethionine made up 30–40% of the total Se in biomass. In both the wild type and Se-resistant strains, the activity of thioredoxin reductase, increased rapidly in the presence of the form of selenium for which the given algal strain was not resistant.ConclusionThe selenium effect on the green alga Scenedesmus quadricauda was not only dose dependent, but the chemical form of the element was also crucial. With sulfur deficiency, the selenium toxicity increases, indicating interference of Se with sulfur metabolism. The amount of selenium and SeMet in algal biomass was dependent on both the type of compound and its dose. The activity of thioredoxin reductase was affected by selenium treatment in dose-dependent and toxic-dependent manner. The findings implied that the increase in TR activity in algal cells was a stress response to selenium cytotoxicity. Our study provides a new insight into the impact of selenium on green algae, especially with regard to its toxicity and bioaccumulation.

Highlights

Selenium is a trace element performing important biological functions in many organisms including humans
Thereafter, the recovered cells showed a higher resistance to selenite than the wild type cells. We selected those cells, which were able to grow in extremely high concentrations of selenium if added in the form of selenite (Figures 1C and 2F)
Selenium toxicity in the wild type cells of the green alga Scenedesmus quadricauda increased with increasing dosage of selenium added as selenite or selenate

Summary

Introduction

Selenium is a trace element performing important biological functions in many organisms including humans. It usually affects organisms in a strictly dosage-dependent manner being essential at low and toxic at higher concentrations. Selenium is a trace element, which affects organisms in a dose-dependent manner. At low levels, it contributes to normal cell growth and function. Unicellular, marine calcifying alga Emiliania huxleyi requires nanomolar levels of selenium for growth and selenite ion is the predominant species used by this alga [10]. The essentiality, is sometimes difficult to estimate because selenium is required at such low levels for most organisms that it is experimentally challenging to generate strong phenotypes of deficiency [13]

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Conclusion