What is our project?
We aimed to create magnetite nanoparticles in Escherichia coli using a synthetic biology approach. Magnetite is an iron oxide that can be formed by organelles called magnetosomes. Magnetosomes are found inside of some species of magnetotactic bacteria (MTB) such as Magnetospirillum gryphiswaldense. Magnetotactic bacteria use magnetite to orientate themselves. By following magnetic fields, MTB can move towards anaerobic environments at the bottom of a body of water. However to date, magnetosomes have not been successfully engineered into E. coli despite numerous potential applications of growing magnetite crystals in Escherichia coli.
Why is it important?
There are many novel applications for nanomaterials and through synthetic biology we can revolutionise the way that they are made. The versatile nano-material, magnetite, has many potential uses. Our main area of interest is drug delivery but it also has uses in electronics and waste management. If magnetite can be grown in Escherichia coli it could potentially produce a sustainable source of magnetite, thereby eliminating the need for mining the mineral or producing it in an environmentally costly chemical reaction. With a synthetic biology approach, using Escherichia coli also potentially allows greater control of nanoparticle size and shape distributions, which would positively contribute to their applications. Our results will also further our fundamental understanding of how bacteria cells are able to form and organise magnetite nanoparticles.
Our results can be seen here.
How did we do it?
We have expressed selected genes associated with magnetite formation in Escherichia coli. The genes MamP, MamT, MamX and MamO encode for proteins that are thought to be involved in the bio-mineralisation of magnetite in the magnetosomes, were engineered into E. coli. The expressed proteins were characterised in vitro and their effect on the cells were characterised in vivo, using two different versions of the gene, respectively. The native gene, which includes a targeting sequence to the membrane was used for the in vivo characterisation and a different sequence that includes a his-tag, with the predicted membrane anchor sequence cleaved was used for the in vitro route. Each gene was expressed individually and then as a set of up to three genes to see what construct was necessary to achieve magnetite formation. For the in vivo experiments, the three genes together with MamO gene encoding for a protein that is thought to nucleate the magnetite particles were engineered into Escherichia coli, and the cells were grown in the presence of iron. For the in vitro experiments, the cells were lysed and the proteins purified in order to test them in an iron rich environment, thereby eliminating the constraints that being cell bound poses.