iGEM-2013 Chiba

iGEM-2013 Chiba

Iron Oxidation


    Nishida et al. first discovered normally diamagnetic yeast Saccharomyces cerevisiae were attracted towards a magnet when grown with ferric citrate1. Because ferromagnetic magnetite (Fe3O4) is mainly responsible for magnetization, the redox state inside the cell is an important factor. In yeast, mgnetification is further enhanced by TCO89 overexpression , which leads cellular redox to more oxidized state.
    On the other hand, in E. coli, there are two proteins called glutathione (gor) and thioredoxin (trxB) play a central role in modulating cellular redox and makes it reductive (detailed mechanisms are described here.)

    From these facts, we could magnetize E. coli by modulating its redox more oxidative state like in yeast. So, we decided to knock down gor and trx to make cellular redox to more oxidized state, in which iron can form ferromagnetic magnetite (Fe3O4) and cells are magnetized.
    1. We first used SHuffle® (NEB) strain derived from E. coli stain BL21 in which gor and trxB is inactivated. And we compared the redox state of thesb two strains (wild type E. coli (BL21) and SHuffle® (NEB)) with a redox indicator, which would change to more blue colour when cellular redox is more oxidized.
    2. Second, we tried to conditionally knock-down these two genes by using CRISPRi system(on going).

2.Materials & Methods


E. coli(BL21)
SHuffle® (NEB)

2.2Evaluation of intracellular oxidative state


3.Results & Discussion

3.1.Evaluation of intracellular oxidative state

1) We found no significant color difference between the colony of two strains with all concentrations of methylene blue used .
2) Both strains showed compromised cell growth in the presence of methylene blue presumably because a higher rate of methylene blue reduction interferes with cellular metabolism.

Fig. 1 Evaluation strain of BL21 and SHuffle®

                Fig. 2 Lift


We could not distinguish the difference of the redox potential by colorimetric assay using redox indicator, methylene blue.