Probing the Role of the Chloroplasts in Heavy Metal Tolerance and Accumulation in Euglena gracilis

Abstract

The E. gracilis Zm-strain lacking chloroplasts, characterized in this study, was compared with the earlier assessed wild type Z-strain to explore the role of chloroplasts in heavy metal accumulation and tolerance. Comparison of the minimum inhibitory concentration (MIC) values indicated that both strains tolerated similar concentrations of mercury (Hg) and lead (Pb), but cadmium (Cd) tolerance of the Z-strain was twice that of the Zm-strain. The ability of the Zm-strain to accumulate Hg was higher compared to the Z-strain, indicating the existence of a Hg transportation and accumulation mechanism not depending on the presence of chloroplasts. Transmission electron microscopy (TEM) showed maximum accumulation of Hg in the cytosol of the Zm-strain and highest accumulation of Cd in the chloroplasts of the Z-strain indicating a difference in the ability of the two strains to deposit heavy metals in the cell. The highly abundant heavy metal transporter MTP2 in the Z-strain may have a role in Cd transportation to the chloroplasts. A multidrug resistance-associated protein highly increased in abundance in the Zm-strain could be a potential Hg transporter to either cytosol or mitochondria. Overall, the chloroplasts appear to have major role in the tolerance and accumulation of Cd in E. gracilis.

Molecular tools and applications of Euglena gracilis: From biorefineries to bioremediation

“…Further to this, the role of the chloroplasts in heavy metal tolerance and accumulation in E. gracilis was revealed (Khatiwada et al, 2020a).…”

“…The increase in abundance of thiol‐rich proteins indicated the ability of E. gracilis to chelate and sequester heavy metals. Further to this, the role of the chloroplasts in heavy metal tolerance and accumulation in E. gracilis was revealed (Khatiwada et al, 2020a).…”

“…Several transporters that may have a role in transporting heavy metals in and out of cell were also identified in the proteomic study conducted with E. gracilis (Khatiwada et al, 2020b). The highly abundant heavy metal transporter MTP2 was found to have a role in Cd transportation to the chloroplasts in the E. gracilis Z‐strain and a multidrug resistance‐associated protein member 2 (MRP2) was highly abundant in the Zm‐strain treated with Hg indicating its role to transport Hg to either cytosol or mitochondria (Khatiwada et al, 2020a).…”

Enhanced Adsorptive Bioremediation of Heavy Metals (Cd2+, Cr6+, Pb2+) by Methane-Oxidizing Epipelon

“…Though some of these techniques are effective in the removal of heavy metals, practical applications are not easily employed on a large scale due to their high cost and the secondary contaminations by the chemicals used in the processes. Several biological methods such as immobilization by biochar and rice straw, hyper accumulator plants, specific functional microbes have already been reported for heavy metals removal [11,12]. However, they require high labor cost and are not fully suitable in many cases under in situ conditions.…”

Genome-wide Identification and Function Analysis of HMAD Gene Family in Cotton (Gossypium Spp.)

“…Moreover, salinity stress overlaps with HMs toxicity to some extent, as several integrated mechanical and chemical signals are responsible for stress-related responses [41]. For example, chloroplast and chlorophyll content can measure salt stress [42], also affect the transport of heavy metals [43,44]. Even avonols have shown the ability in alleviating toxic effect of Pb and improving the resistance of plants, because it activated anti-oxidative process [45].…”