Comparison of cell size, chlorophyll fluorescence and cadmium (Cd2+) bioaccumulation between wild-type and mutant strains of Chlamydomonas reinhardtii upon exposure to Cd2

Abstract

Background: Heavy metal contamination presents a constant threat to biological systems. Simultaneously, heavy metals have become one of the major contaminants in the aquatic ecosystems. In this regard, the investigation of heavy metal-tolerance genes in algae is relevant. Chlamydomonas reinhardtii is a unicellular green alga, and an excellent model organism used in heavy metal studies. In C. reinhardtii, a novel gene designated as Cia7, was hypothesized to play a role in heavy metal homeostasis due to CIA7’s conserved cysteine-residue motif. This study compared two strains of C. reinhardtii, cc4425, the wild-type with the functional CIA7 protein and cc5013, the mutant strain with the disrupted cia7- gene. The hypothesis was that the expression of Cia7 contributes to an increased cadmium (Cd)-tolerance in C. reinhardtii. The Cd-tolerance would be described by physiological markers of microalgae health, and by intracellular accumulation of the metal. Methods: The objectives of this study were (1) to compare chlorophyll fluorescence and cell size in cc4425 and cc5013 exposed to Cd2+, and (2) to compare Cd2+ bioaccumulation in cc4425 and cc5013 strains in different growth media. Flow cytometry, and inductively coupled plasma optical emission spectrometry (ICP-OES) analysis were performed. Results: There was no significant statistical difference in Cd2+ bioaccumulation between the two strains, cc4425 and cc5013, regardless of growth media. However, a statistically significant difference in Cd2+ bioaccumulation (p<0.0001) was determined between the media (with acetate and without acetate). The cia7- mutant, cc5013 was found to be more susceptible to a Cd2+-induced decrease in chlorophyll fluorescence and had a reduced cell size compared to cc4425, the wild-type strain. Conclusions: These observed differences between the strains suggest that CIA7’s biological activity could play a direct or indirect role in increasing Cd tolerance in C. reinhardtii.

Comparison of cell size, chlorophyll fluorescence and cadmium (Cd2+) bioaccumulation between wild-type and mutant strains of Chlamydomonas reinhardtii upon exposure to Cd2+

“…A novel gene, Cia7, was isolated from an inorganic carbon-acquiring, and high carbon dioxide-requiring C. reinhardtii mutant, cc5013 (Ynalvez and Moroney, 2008). The gene designated as Cia7 was hypothesized to play a role in heavy metal tolerance or metal detoxification due to its translational product's amino acid sequence.…”

“…Homologous proteins also included computer modeling predicted proteins, TRAP transporter small permease (92% identity) and an uncharacterized metal binding protein (72% identity). The protein sequence of CIA7 contained a conserved, repeated motif of four cysteine residues whose thiol functional group is hypothesized to chelate heavy metals (Ynalvez and Moroney, 2008). Based on this observation, the aim of this study was to investigate whether Cia7 plays a potential role in metal tolerance in C. reinhardtii.…”

“…Underlying data Dryad: cell size, chlorophyll fluorescence and cadmium bioaccumulation between wild-type and mutant strains of Chlamydomonas reinhardtii upon exposure to cadmium, https://doi.org/10.5061/dryad.rn8pk0pb4 (Ynalvez et al, 2021).…”