Team:Calgary/Description

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Our Project

The Problem

Governments and private enterprises alike are gearing up for travel across our Solar System. Plans to colonize nearby planets are underway, with Elon Musk spearheading the initiative to put a human colony on Mars by 2030. In a parallel vein, NASA is planning a manned exploratory mission to Mars as soon as the 2030s. Several other space agencies have similar plans and timelines for their own respective Mars explorations. This exciting time in our history nonetheless comes with the challenges of long-term space travel.

Two ecological and economic challenges arise:

  1. the sustainable management of waste produced in space, and
  2. the high cost of shipping materials to space.

Waste management on Mars will be paramount because manned missions will need to recover as much water and oxygen as possible to sustain life. Human waste must also be treated to minimize health risks for the crew of a Mars mission. All of this must be accomplished while preserving the natural Martian environment.

The current cost of shipping materials up to space is $10,000 USD per pound due to the high price of fuel (Hsu, 2011). This expense will constrain early Mars mission crews in the supplies that they can bring or ship from Earth to Mars, and may not allow astronauts to account for every tool they may require during their mission. One way to mitigate this challenge is to develop a system to produce necessary items in space as needs arise.


Our Solution

Our team is working on a unique solution to both of the aforementioned challenges of future Mars missions: we intend to upcycle human waste by using it as a feedstock for E. coli engineered to produce bioplastic, which can then be 3D printed into useful tools onsite.

Poly(3-hydroxybutyrate) (PHB), a bioplastic, is produced in nature by many bacterial species. Literature has shown that PHB can be produced using a variety of feedstocks, including glucose and volatile fatty acids (VFAs) (Albuquerque et al., 2011). Since human waste contains both glucose and VFAs, it is a potentially useful feedstock for PHB production.

Our team engineered E. coli to express PHB-producing genes, which we codon-optimized to increase the efficiency of PHB production. We then modified native E. coli secretion pathways so the cells would release the PHB they produced. This allows for a continuous PHB production and secretion process, as opposed to a traditional batch process, which is not user-friendly and requires more time and maintenance. When employed together, these genetic modifications create a novel means of bioplastic production.

We also developed a start-to-finish process involving both waste management and PHB production. In the first step of this process, solid human waste is collected and fermented with naturally occurring enterogenic bacteria to increase the concentration of VFAs. As a part of this process, the solids from the waste settle and the liquid rises to the surface of the fermentation tank. Next, the VFA-concentrated liquid in the fermentation tank is separated from the solid particles by centrifugation, sterilized by filtration, and passed to a bioreactor containing our engineered PHB-producing E. coli. Once the PHB is synthesized and secreted, it can be continuously collected and extracted from the liquid stream. The resulting liquid can be recycled into drinking water, while PHB particles can be used in a Selective Laser Sintering (SLS) 3D printer to generate items useful to astronauts.

This overall process is summarized below. Find more information on our Process Development page!


ModelAnimationDesign6 ON BIOREACTOR STIRRED-TANK EXTRACTION SEPARATION Finish Start In the first step of our process, astronaut feces are deposited into a vacuum toilet and collected in a storage tank before they are passed on to the first bioreactor. The fecal matter is then fermented by natural gut flora for three days at room temperature. This results in the production of volatile fatty acids (VFAs) and the breakdown of carbohydrates to produce glucose, which can both later be used as a feedstock for our PHB-producing, engineered E. coli. In the next stage, the nutrient-rich liquid stream is obtained by separating it from solid particles. This is achieved with centrifugation to remove solids followed by filtration to remove any natural gut flora that may outcompete our engineered E. coli. The solid particles may be recycled later after additional processing as radiation shielding, building materials, food substrates, or stores of carbon and hydrogen. In this stage, continuous fermentation of the nutrient-rich stream occurs in a stirred-tank bioreactor inoculated with PHB-producing E. coli. These engineered bacteria convert glucose and VFAs in the nutrient-rich feedstock to PHB using the phaCBA and phaC1J4 operons, respectively. The resulting PHB granules are secreted from E. coli by taking advantage of its native Type I secretion pathway. A recombinant phasin-HlyA fusion protein was designed aid in this process. Exogenous phasin electrostatically binds to PHB particles, while the fused HlyA tag is recognized by endogenous membrane transport proteins HlyB, HlyD, and TolC. The PHB-phasin-HlyA unit is then secreted by these transport proteins as a whole. In the final stage of the process, secreted PHB particles are separated from liquid media via dissolved air flotation. Water oversaturated with air is bubbled through the media in a flotation column, allowing the PHB particles to float to the top. This upper phase containing PHB is then passed to a drying unit, where moister is removed and recycled. Finally, PHB is obtained in powdered form and is ready for 3D printing. Click on the boxes above to learn more!

Works Cited

Albuquerque, M.G.E., Martino, V., Pollet, E., Avérous, L. & Reis, M.A.M. (2011). Mixed culture polyhydroxyalkanoate (PHA) production from volatile fatty acid (VFA)-rich streams: Effect of substrate composition and feeding regime on PHA productivity, composition and properties. J. Biotechnol., 151(1): 66-76

Hsu., J. (2011). Total Cost of NASA's Space Shuttle Program: Nearly $200 Billion. Space.com (Magazine). Retrieved September 17, 2017, from https://www.space.com/11358-nasa-space-shuttle-program-cost-30-years.html