Simultaneous removal and optical determination of mercury ions by constructing fluorescent recombinant T. thermophila SB210 strains

Removing and monitoring Hg 2+ ions in the pollution sources based on microorganisms have the advantages of low cost and convenience. To reduce the harm of Hg 2+ ions to humans and ecosystems in the environment, it is considered very meaningful to establish a biological treatment method using protozoa to simultaneously detect and remove Hg 2+ ions in polluted water. In this work, the coding region of MTT1 and MTT5 genes in Tetrahymena thermophila SB210 ( T. thermophila SB210) was replaced with green fluorescence protein ( GFP ) gene using genetic manipulation techniques. Fluorescent recombinant T. thermophila SB210 strains MTT1-GFP and MTT5-GFP were constructed, and the relationship between MTT1-GFP and MTT5-GFP and the effect of simultaneous response and removal of Hg 2+ ions was explored. The knockout of MTT1 and MTT5 genes and introduction of GFP significantly reduced cell tolerance to Hg 2+ ions, slightly increased the removal rate of Hg 2+ ions, and induced fluorescence response to Hg 2+ ions. Using MTT1-GFP at a cell density of 150 × 10 4 cells mL −1 , the removal rate of Hg 2+ ions were over 90 % at range 6000 μg L −1 to 10000 μg L −1 in 12 h. The limit of detection (LOD) was 1.063 μg L −1 and the linear detection range of Hg 2+ concentration was 200–8000 μg L −1 using MTT1-GFP as fluorescence reporter. In addition, the different functional effects of MTT1-GFP and MTT5-GFP on Hg 2+ and Cd 2+ were compared. This study will expand our understanding of the role of MTT1 and MTT5 genes and provide a method for simultaneous response and removal of Hg 2+ ions in water bodies using T. thermophila .