Functional Characterization of the Novel Gene CIA7 from Chlamydomonas Reinhardtii
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Heavy metal contamination presents a constant threat to biological systems. These metals interact with the catalytic-domain of enzymes, interfering with their normal rates of activity as well as inducing oxidative stress. Chlamydomonas reinhardtii is an excellent model organism used in studies of heavy metals due to its high endogenous tolerance. In C. reinhardtii, a novel gene, designated as CIA7, was isolated and hypothesized to confer tolerance to heavy metals. This was due to CIA7’s conserved Cys-residue motif and its homology in a number of bacterial metal binding proteins. This study aimed to demonstrate what role CIA7 exerts on tolerance towards Cd2+ stress in C. reinhardtii. The hypothesis was that the expression of CIA7 will contribute, at least in part, to an increased Cd-tolerance in C. reinhardtii, described by physiological markers of health, as well as intracellular accumulation of the metal. To functionally characterize CIA7: (1) comparative studies of chlorophyll fluorescence and cell size in WT and cia7- in the presence of Cd2+, (2) comparative studies of Cd2+ bioaccumulation in WT and cia7- strains in various growth media, and (3) Cd2+ tolerance assays in WT overexpressing CIA7 were performed. The cia7- strain was more susceptible to Cd2+ induced decreased chlorophyll fluorescence and reduced cell size than the WT, and no significant difference in bioaccumulation was observed amongst the strains, although a significant effect of the growth media on the concentration was observed. Approximately 200 WT pSL72cia7- transformants were generated, which were subsequently preliminary screened for cadmium tolerance. The characterization of CIA7 as a metal-binding protein would allow for its potential use as a metal sequestering agent in environmental applications. Furthermore, a correlation of heavy metal exposure to CIA7 expression could designate CIA7 as a biomarker for heavy metal contamination.