Phenotypic Analysis of Chlamydomonas reinhardtii Supplemented with Sublethal and Toxic Levels of Cd

Cd is a metal not normally utilized by organisms and is toxic to most cells. The nearly irreversible reactivity of Cd with thiol groups is the key feature that makes it a toxic chemical, which explains why organisms have developed detoxifying pathways to prevent free Cd from reacting and damaging cells. For example, Chlamydomonas reinhardtii produces phytochelatins, which will bind and sequester intracellular Cd. The pathways activated by Chlamydomonas upon exposure to Cd and the methods for Cd uptake are not well understood and are under investigation. Chlamydomonas serves as a reference experimental organism because it displays phenotypic responses to stress and its genome has been sequenced. Cd supplementation concentrations have been chosen to obtain no activity (0μM Cd), Cd-specific activity (25μM Cd), and Cd-saturated activity (120μM Cd) of the heavy metal detoxification pathways in wild-type cells. Cell samples collected from cultures supplemented with 120μM Cd show a significant decrease in growth and chlorophyll content and a hyperaccumulation of trace metals relative to samples supplemented with 25μM and 0μM Cd, both of which display similar results. RNA was isolated from cells grown in the three conditions mentioned at 0, .5, 1, 2, 4, 6, and 24 h after supplementation. Subsequent analysis of the mRNA using RNA-Sequencing will be performed to analyze the mRNA expression at a whole genome level and identify the genes encoding proteins that participate in pathways regulated by various concentrations of Cd.