Future of our Filtration System

How can we deal with the waste associated with our filtration system?

After preliminary discussions with an employee from BQE Water, a water treatment company specializing in providing innovative wastewater treatment solutions to the global mining industry. They suggested that it was important to consider the fate of the metal ions following binding to the pilus. After use of our metal binding reactor, we would be left with a metal bearing biosolid containing both metal and bacteria. BQE Water suggested that we could mix these biosolids with anaerobic digesters that deal with municipal water treatment biosludge. Alternatively we could apply different solution conditions to the biosolids and then desorb the metal in a more concentrated form.

We researched the potential to wash our bacteria with Ethylenediaminetetraacetic acid (EDTA), a chemical commonly used for both industrial and medical purposes, and is found everywhere from fertilisers to shampoo. EDTA can be bought as a disodium salt and will react with other metals in solution. EDTA is a very potent metal-chelating agent and the metal ions bound to our binding proteins will bind preferentially to the EDTA and so be transferred into an EDTA complex (Nyborg,2004). EDTA is also being explored for its anti-microbial properties and is likely to irreversibly damage our bacteria and their biofilms (Finnegan, 2015). Therefore, when used in conjunction with other biosecurity methods, washing our system with EDTA would help to terminate our modified bacteria while resulting in a solution of EDTA bound to metal ions.

Metals bound to EDTA are commonly sold for purposes ranging from bleaching (in the case of cadmium disodium edetate) to fertiliser (in the case of iron disodium edetate and many others). Looking on Alibaba.com, our reactant – disodium EDTA can be bought for between $1530-5000 per tonne, while zinc disodium EDTA can be sold for between $1900-5000 per tonne to give just one example. Therefore, disodium edetate could be bought for $1530 per tonne, used to wash our bacteria modified with a zinc binding protein, and be sold on as zinc disodium edetate (used as fertiliser) for as much as $5000.

Therefore, by washing our bacteria with EDTA after use, our filter system will not only clean water, but as a bi-product will produce fertiliser which can be sold on to mitigate the costs of running the filter.

There is very little risk of contaminating local water sources with EDTA in the case of a spill as EDTA degrades in shallow water through direct photolysis when exposed to wavelengths of less than 400nm, commonly found in sunlight (Wikipedia, 2017).

To assess the suitability of EDTA in our project, we would have to carry out experiments to test the success in removing metal ions from the metal binding proteins we have inserted on our modified pili.

Will our E. coli be resistant to the low PH of contaminated mine water?

Through our field trip to the Wheal Maid mine site we became aware of quite how acidic the polluted mine water we aim to filter is. The water at that site had a PH of 3. We are aware of that our genetically modified E. coli may not be resistant to such acidic water. However, whilst our choice of E.coli gave us the ability to show the proof of concept, it does not necessarily need to be the chassis organism in the future. It may be beneficial to use this concept in a more resistant organism.

On speaking to representatives from Greenpeace, it was suggested to use to look into the bacteria that live in the reed beds at the Veolia mine site as these are clearly resistant to the highly acidic water. For example: Pseudomonas azotoformans, Pantoea agglomerans could be used as an alternative.

How are we going to ensure that our product takes into account biosecurity measures?

Our experiments into the effectiveness of UV radiation as a bactericide showed that it was not suitable for use in our filtration system. This was due to two reasons. Firstly it took over 10 minutes to see a significant reduction in the population of E. coli, these findings were confirmed by a collaboration with Cardiff University iGEM team. Secondly at a lecture we attended at the iGEM UK meet up, it was stated that the escape frequency allowed by industry was 10^-6 The results we obtained demonstrated that the UV was not powerful enough to reach anywhere near this standard.

References

Nyborg J.K. and Peersen O.B., (2004), That zincing feeling: the effects of EDTA on the behavioour of zinc-binding transcriptional regulators

Finnegan S. and Percival S.L., (2015), EDTA: an antimicrobial and antibiofilm agent for use in wound care

Wikipedia,(2017),Ethylenediaminetetraacetic acid, Available at: https://en.wikipedia.org/wiki/Ethylenediaminetetraacetic_acid