| Depending on the chemistry of the environment, selenium can be present in different oxidation states altering its bioavailability as it forms different chemical species. Chlorella vulgaris is an alga that is known for its ability to accumulate metals and this thesis explores the ability of Chorella to bioconcentrate and detoxify different species of selenium. Selenate was more bioavailable to Chlorella vulgaris than selenite at exposures of 10 mu/mL when sulfate was present at low concentrations (3 mg/L) in the growth medium. Selenate was bio-transformed by Chlorella vulgaris cultures into several different reduced species, including selenite. This biotransformation process was inhibited when high concentrations (30 mg/L) of sulfate were present in the medium which was likely due to competition between selenate and sulfate ions during uptake into the cytosol. Chlorella vulgaris also produced the potential detoxification compounds phytochelatins, when exposed to selenate. This was confirmed by a novel method, which was developed to accurately quantify and extract phytochelatins. Phtochelatin-2 and phytochelatin-3 were present at concentrations that ranged from 1x10-10-1x10 -8 moles per cell. High concentrations of sulfate in growth medium inhibited the selenate-induced production of phytochelatins, which is consistent with the sulfate inhibition of biotransformation. Both a negative feedback loop involved in sulfate uptake and metabolism, and sulfate/selenate competitive inhibition may be responsible for the results obtained. These results indicate potential for phytoche1atins in Chlorella vulgaris to playa role in metal detoxification in aquatic ecosystems that have had low impacts from environmental sulfate, such as in areas affected by acid mine drainage and acid rain.Keywords: Selenium, sulfur, Chlorella Vulgaris, phytochelatins, mass spectrometry, chromatography... |
