Team:Brno Czech Republic/Implementation

Proposed Implementation

Implementation


Figure 1.: New phosphate cycleThe main functional component of our Phoscage device is genetically modified Bacillus subtilis, forming BMCs in which phosphorus is captured (as described in Project description). The intention is to sequester phosphorus from water, either from wastewater in sewage treatment facilities (here phosphorus from households and industry would be captured) or in open water bodies (here phosphorus washed from agricultural areas would be captured and cyanobacterial overgrowth would be reduced).


3D bioprinting


Figure 2.: 3D print of biofilm Bacillus subtilis will either fill a chamber in a floating apparatus or a tank in the wastewater treatment plant. To achieve an efficient and robust system, we decided to use the 3D bioprinted biofilm. Bacillus subtilis, like many other bacteria, naturally lives in biofilm and thrives in it. Modern technology makes it possible to work with biofilm further. The bacteria forming the biofilm are mixed with natural polymers such as hyaluronic acid or κ-carrageenan. The resulting bio-ink can be then 3D printed into different shapes (5). This approach has even already been used in wastewater treatment. In wastewater treatment, where we use bacteria as a kind of "biofilter", the functional surface area is very important, and 3D particle printing allows us to design and easily print out a structure with extremely large surface area (6).


It would also be possible to use microcarriers other than the biofilm itself to increase the surface area, but given our intention to recycle the phosphorus, it is advisable to limit the amount of artificially added components. Natural waste materials such as unused husks and skins from grain, corn or rice could be considered. These could themselves be used in fertilisers after incineration. In this case, the low cost is an advantage. The disadvantage of these natural materials compared to 3D printing is the inability to ensure optimal interaction between water and biofilm or low buoyancy in the water column (6).


Bacteria contained in biofilm would be in contact with water and thus be able to accumulate phosphates until the BMCs are filled or the bacteria die. So far we believe it could be used continuously for a couple of days. During these days the device would be submerged in water. In regular intervals, the biofilm would be lifted out of the water and replaced with a new one. Used biofilm filters would be taken away for processing for further use.


GMO Safety


As we use GMOs in our system, safety precautions must not be forgotten. The issue of GMOs resonates with the public and that is why we asked them about their opinion on safe use of GMOs in our questionnaire (detailed in Human Practices). We asked about the degree of inactivation of GM bacteria. 9,5% of respondents are in favour of simply killing the bacteria, 33,6% of respondents additionally require thorough degradation of bacterial DNA. A minority also require more complex isolation of BMCs or phosphorus.



Figure 3.: What would be sufficient "inactivation" of GMOs for you? (the numbers in the graph indicate the number of respondents, not percentages)


Figure 4.: Would you agree with the use of phosphates produced by our engineered bacteria in the chemical industry?


The phosphorus obtained in this manner can be used in many ways such as in fertilizers or as a raw material in the chemical industry. We also asked the public about this in the aforementioned survey. Overall, we can conclude that people are in favour of using phosphorus obtained by our device. When respondents took into account the fact that phosphate was isolated using GM bacteria, they mostly preferred its use in the chemical industry 74,3%. But use in fertilizing industrial crops 63,6% and food 39,9% was also viewed quite positively. Some 58,1% would even use our phosphorus to fertilise their own plants in the garden.


Figure 5.: Would you agree with the use of killed GMOs as fertilizer for industrial crops?


Figure 6.: Would you agree with the use of killed GMOs as fertilizer for food crops?

Final product

So what is the possible end use of our product - B. subtilis cells with BMCs loaded with polyphosphate? Overall, we have two products in mind: a mineral fertilizer and a home compost enrichment product.

  1. Mineral fertiliser would be produced by ashing the collected biomass. This will lead to the absolute inactivation of GM bacteria and will allow us to obtain an inorganic form of phosphate, which is widely used in fertilisers and easily accessible to plants.

  2. The second product would only involve the inactivation of the bacteria and the degradation of their DNA at a temperature of around 190 °C (7). All nutrients, including organic matter, would be preserved. This product could be added to composts to enrich them with phosphate. Organic fertilisers are better for plants because they are more complex and lead to better plant development. On the other hand, it is more difficult for the plant to process nutrients in organic form, so the organic fertiliser must be supplemented with soil bacteria that break down the nutrients into a form that is accessible to the plant. GM B. subtilis must be inactivated for safety reasons and therefore we suggest mixing it with natural compost to ensure the presence of natural soil bacteria.


Literature

  1. 2.Reinhard, C., Planavsky, N., Gill, B. et al. Evolution of the global phosphorus cycle. Nature 541, 386–389 (2017). https://doi.org/10.1038/nature20772

  2. Phosphorus: Essential to Life—Are We Running Out?. State of the Planet [online]. Available at: https://news.climate.columbia.edu/2013/04/01/phosphorus-essential-to-life-are-we-running-out/

  3. Yuan, Z., Jiang, S., Sheng, H., Liu, Xin, Hua, H., Liu, Xuewei, Zhang, Y., 2018. Human Perturbation of the Global Phosphorus Cycle: Changes and Consequences. Environ. Sci. Technol. 52, 2438–2450. https://doi.org/10.1021/acs.est.7b03910

  4. The next big war might be over phosphorus | Grist. Grist.org: Climate. Justice. Solutions. | Grist [online]. Copyright © 1999 [cit. 03.10.2021]. Available at: https://grist.org/food/the-next-big-war-might-be-over-phosphorus/

  5. Schaffner, M., Rühs, P.A., Coulter, F., Kilcher, S., Studart, A.R., 2017. 3D printing of bacteria into functional complex materials. Sci. Adv. 3, eaao6804. https://doi.org/10.1126/sciadv.aao6804

  6. Elliott, O., Gray, S., McClay, M., Nassief, B., Nunnelley, A., Vogt, E., Ekong, J., Kardel, K., Khoshkhoo, A., Proaño, G., Blersch, D.M., Carrano, A.L., 2017. Design and Manufacturing of High Surface Area 3D-Printed Media for Moving Bed Bioreactors for Wastewater Treatment. Journal of Contemporary Water Research & Education 160, 144–156. https://doi.org/10.1111/j.1936-704X.2017.03246.x

  7. Karni, M., Zidon, D., Polak, P., Zalevsky, Z., Shefi, O., 2013. Thermal Degradation of DNA. DNA and Cell Biology 32, 298–301. https://doi.org/10.1089/dna.2013.2056

    Igem Team Brno, Czech Republic 2021