Morphological Indicator for Directed Evolution of Euglena gracilis with a High Heavy Metal Removal Efficiency

Environ Sci Technol. 2021 Jun 15;55(12):7880-7889. doi: 10.1021/acs.est.0c05278. Epub 2021 Apr 29.


In the past few decades, microalgae-based bioremediation methods for treating heavy metal (HM)-polluted wastewater have attracted much attention by virtue of their environment friendliness, cost efficiency, and sustainability. However, their HM removal efficiency is far from practical use. Directed evolution is expected to be effective for developing microalgae with a much higher HM removal efficiency, but there is no non-invasive or label-free indicator to identify them. Here, we present an intelligent cellular morphological indicator for identifying the HM removal efficiency of Euglena gracilis in a non-invasive and label-free manner. Specifically, we show a strong monotonic correlation (Spearman's ρ = -0.82, P = 2.1 × 10-5) between a morphological meta-feature recognized via our machine learning algorithms and the Cu2+ removal efficiency of 19 E. gracilis clones. Our findings firmly suggest that the morphology of E. gracilis cells can serve as an effective HM removal efficiency indicator and hence have great potential, when combined with a high-throughput image-activated cell sorter, for directed-evolution-based development of E. gracilis with an extremely high HM removal efficiency for practical wastewater treatment worldwide.

Keywords: directed evolution; imaging flow cytometry; machine learning; microalgae; single-cell analysis; wastewater treatment.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Biodegradation, Environmental
  • Euglena gracilis*
  • Flow Cytometry
  • Metals, Heavy*
  • Microalgae*


  • Metals, Heavy