Overexpression of the sulfate transporter‐encoding SULTR2 increases chromium accumulation in Chlamydomonas reinhardtii

Abstract

Hexavalent chromium [Cr(Ⅵ)] is a highly toxic contaminant in aquatic systems, and microalgae represent promising bioremediators of metal-containing wastewater.However, the metal-binding capacity of algal cells is limited. Therefore, we improved the cellular Cr(Ⅵ) biosorption capacity of Chlamydomonas reinhardtii by overexpressing the sulfate transporter gene SULTR2. SULTR2 was predominantly located in the cytoplasm of the cell, and few proteins mobilized to the cell membrane as a Cr transporter under Cr stress conditions. Intracellular Cr accumulation was almost doubled in SULTR2-overexpressing transgenic strains after exposure to 30 μM K 2 Cr 2 O 7 for 4 d. Alginate-based immobilization increased the rate of Cr removal from 43.81% to 88.15% for SULTR2-overexpressing transgenic strains after exposure to 10 μM K 2 Cr 2 O 7 for 6 d. The immobilized cells also displayed a significant increase in nutrient removal efficiency compared to that of freeswimming cells. Therefore, SULTR2 overexpression in algae has a great potential for the bioremediation of Cr(Ⅵ)-containing wastewater.

Engineering Aspergillus niger for Effective Bioremoval of Hexavalent Chromium from Water

“…Previous research has reported that chromate, being analogous to sulfate, is actively transported across the cell membrane via sulfate permease in certain microorganisms. 41,42 However, the proteins responsible for chromate/sulfate uptake in filamentous fungi, including A. niger, have remained unidentified.…”

“…The mentioned studies provide compelling evidence that the activity of Cr­(VI) reductase is primarily localized in the cytoplasmic fraction of A. niger cells, indicating that Cr­(VI) in aqueous environments needs to be translocated into the cytoplasm before it can be reduced by cytoplasmic chromate reductase. Previous research has reported that chromate, being analogous to sulfate, is actively transported across the cell membrane via sulfate permease in certain microorganisms. , However, the proteins responsible for chromate/sulfate uptake in filamentous fungi, including A. niger , have remained unidentified.…”

The Microalgae <em>Chlamydomonas </em>for Bioremediation and Bioproduct Production

“…reinhardtii has shown a significant capability for biosorption, effectively removing copper, boron, and manganese [64], arsenic [65], nickel [66], zinc, cadmium [67] and uranium [68]. In C. reinhardtii gene manipulation has been conducted to enhance the expression of the metal tolerance proteins metallothioneins [69], resulting in increased tolerance to cadmium [70], chromium [71], copper [72], mercury [73], and lead [74]. Biosorption in C. reinhardtii as a defense mechanism against silver nanoparticles involves an increase in phytochelatin and exopolysaccharides content, along with a decrease in glutathione levels [75].…”