Probing the role of the chloroplasts in heavy metal tolerance and accumulation in Euglena gracilis

Bishal Khatiwada, Mafruha T. Hasan, Angela Sun, Karthik Shantharam Kamath, Mehdi Mirzaei, Anwar Sunna, Helena Nevalainen

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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.

Original languageEnglish
Article number115
Pages (from-to)1-18
Number of pages18
Issue number1
Publication statusPublished - Jan 2020

Bibliographical note

Copyright the Author(s) 2020. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.


  • Euglena gracilis
  • microalga
  • heavy metal accumulation
  • mercury accumulator
  • transmission electron microscopy (TEM)
  • Microalga
  • Transmission electron microscopy (TEM)
  • Heavy metal accumulation
  • Mercury accumulator


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