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Revision as of 15:21, 13 October 2018
Engineering fungal mycelium to create viable building materials for on Mars is not a small challenge. This project, which was inspired by conversations with Lynn J. Rothschild from NASA, whom we owe thanks both for the inspiration and subsequent sparring on ideas, has relied on a several scientific fields to try to tackle the problems we have found along the way. Our design inspired by the idea of simple and cost-effective construction on Mars, which its simplest terms says that instead of spending millions if not billions on transporting the materials needed for habitats to Mars, one could instead bring a set of vials: One vial with a cyanobacteria, which will harness the carbon in the atmosphere and the oxygen in the martian ice to create biomass that can be used as ‘substrate’ for fungal cultures to create range of biomaterials. Our project focussed on the fungal aspect of such a system and how it could be used to create building materials for habitat construction on-site. This exciting challenge raises many questions that have to be answered and even more problems have to be dealt with. First off, how does one cultivate fungi on Mars? Moreover, Which fungal species should we use? How do we make the system cost-effective? Are the strength of fungal materials determined by any distinct genes and it is possible to regulate these in a way that will make our materials even tougher? We set out to answer these questions, the answers of which guided the creation of our final design
Building Buildings on Mars
How to build buildings on Mars
When the first Martian settlers arrive, They’ll want to erect livable habitats; buildings. When using conventional construction methods, they’d be restricted to either having to use heavy machinery in order to move local building materials, or having to bring the construction materials with them. Both options are an expensive cut in the weight and volume budget of any space mission, where, especially, mass is the key parameter of the mission cost.
This Projects’ novel approach is for the astronauts to pack a bag with fungal spores, in order for them to bring a super lightweight building material that is able to quickly grow into any shape by the aforementioned procedure in the first section.
An obvious question is then: What physical parameters will the fungal bricks have to withstand, for them to be used as building material on Mars? Initially, constructed as a building, they’d have to be able to contain a livable pressures. The average pressure on earth is 1.013 bar with 21% oxygen. The lowest “human life sustaining” pressure is 0.121 bar, assuming a 100% oxygen concentration. The average Martian pressure is 0.006 bar. This is a meere 0.6% of the average barometric pressure on earth.
What building design/geometry is the best at containing pressures? Let’s investigate a dome design and a box design.
Fig. 1: - Dome structure
Volume: 30m3
Area: 48.6 m2
Fig. 2: - Box structure
Volume: 30m3
Area: 62 m2
Based on this small review, using an arbitrary volume, it was concluded that the dome is the superior design for the building geometry. Reasons are as follows: It uses less building material per volume, the strength demand is lower in the dome because of the force build-up in the corners in the box; demanding a stronger brick material for the box design. The dome is as a whole intrinsically better at distributing the forces throughout the structure. The dome can be constructed from a singular unitary brick design; the triangle.
A dome can be constructed from a mix between hexagons and pentagons, but it turns out that if the dome is constructed from triangles, it is stronger and it is more convenient to only need to bring one mold for the bricks.
After having sifted through the literature, it was decided that we are aiming to build and simulate a 3v dome. This means that the dome is constructed from two kinds if triangles with only slightly different side lengths. the combination of side lengths are as follows: AAB and BCC, where each letter denotes a distinct length. Our Final Brick design was based on these triangles with a meshing pattern, so that the triangles wouldn’t need additional materials to hold them together. They do it by utilising friction fit. When a dome has been erect, it would be sprayed with some curing agent, making the structure air-tight.
Fig. 3: - Triangle sizes
Fig. 4: - Triangle dome structure
Determining fungal material properties
When determining material properties, experiments are critical. Depending on how many parameters you want to examine, the number of experiments tend to exponentially increase. Using Fedorov Exchange Algorithms we were able to reduce our experiment-space (number of experiments), in the first run, from 216 to 64 and in the second run from 648 to 68, which, as you can imagine, is a huge time saver.
It became clear to us that we needed to produce a lot of fungi sample/”cubes”.
Initially, we fabricated some acrylic boxes. These were fast and easy to make. It turns out that acryl does not withstand the pressures and temperature when the fungi gets autoclaved. We turned to metal. These metal boxes took a long time to make, and after having fabricated 11, it was decided that the effort would not be worth it. After having done some research, silicone ice cube trays turned out to be the perfect alternative to our metal boxes. Silicone can easily withstand autoclaving and allowed for very uniformly shaped samples.
The test samples/ fungi cubes were all prepared in slightly different ways, according to our experiment optimization: Baking times, compound composition, substrates etc. All the samples were subjected to a destructive compressional test, where the stress/strain-curve was determined for compressional strength. In order to obtain the Young’s Modulus of the fungi, the tensile strength would also have to be measured. When you know Young’s Modulus, you have the insights of the entire materials’ properties and characteristics.
How to grow fungi on Mars
Growing living organisms and specifically fungi extraterrestrially can be challenging, as the surface of Mars is really hostile. In addition to the extreme cold, there is little atmosphere to speak of and virtually no oxygen. In our attempt to tackle these challenges we aim to introduce cyanobacteria in these extreme conditions.
To start with, cyanobacteria are thought to have played a pivotal role in the evolution of Earth’s atmosphere. Their biological functions are facilitated by producing oxygen, nutrients and vitamins through photosynthesis which in turn can led in to the formation of a human-friendly environment. Therefore, our general plan is to use cyanobacteria which would convert the ample supplies of Mars’ CO² into oxygen, reducing carbon dioxide and at the same time making human occupancy a valid possibility. Seeding Mars’ atmosphere with cyanobacteria, can lead to the conversion of its most abundant gas into something breathable for humans which will at the same time serve as a growing substrate for living organisms.
We hope that one day, manned missions will be able to take advantage of the oxygen created by these bacteria by either combining it with nitrogen to create breathable air or by using it for consumption over and over again.
Choice of organism
The choice of organism used in our project was based on an inductive strategy. We had two variables needed to be fulfilled in our attempt to achieve the goals that we had set. The first one was to find a fungi species that when given the right substrate would have the ability to form firm brick structures. The second one was to use a microorganism that would have its genome sequenced and thus enabling it to withstand genetic modifications. The project started with three candidates-organisms: Pleurotus Ostreatus, Aspergillus Oryzae and Schizophyllum Commune. Our choice ended up being relatively simple as the results taken from every candidate except from A.oryzae, were off the mark compared to our initial expectations. Briefly, Aspergillus oryzae when given rice as a substrate could form strong and firm bricks accompanied with swift spore formation. A possible explanation of this feature could be that Aspergilli can release a variety of enzymes that are capable of breaking down their substrate into simpler compounds, absorbing them through their vegetative hyphae. The hyphae when being in a favorable environment (moisture, warmth and nutrients) allows the fungi to grow, spread and continue reproducing across the surface of the substrate and eventually taking the shape of the engulfing container.
Furthermore, Aspergillus oryzae belongs to a family of fungi that has been used vastly in a lot of aspects of the industry. Species belonging in the Aspergillus family, prosper in a variety of different climates around the world and have a variety of different applications ranging from microbial fermentations to medicinal applications. What is more, Aspergilli have low pathogenic potential as they do not produce aflatoxins or any other cancerogenic metabolites, making the conduction of safe laboratory experiments possible.
Improving the fungal materials through synthetic biology
When using fungal mycelium and organic materials as the basis for your building materials, a new venue of possibilities suddenly appear. The fungi is genetically modifiable, which allows for tuning of different external parameters or even adding properties such as biosensors etc.
The interesting question to answer is this respect is: What genetic modifications are beneficial when it comes to construction on Mars?
Like any other organism, any fungi is optimized for the survival of its species in its niche. No fungal strain is solely optimized for creating strong materials, as that wouldn’t be a advantageous evolutionary strategy. By making the fungi a little worse at surviving we aim to make it better at building
Understanding morphology and the environment under which it lives is pivotal for identifying potential gene candidates
(Briefly on fungal morphology, The strength of fungal cell walls is provided by its a)
In our project we ended up focussing especially two genes, melA and gfaA.
Protection from UV radiation and Melanin
One part of what makes Mars as harsh environment is radiation. Unlike the terrestrial atmosphere, the martian atmosphere does not shield well against cosmic radiation. Among such kind of radiation in UV light (higher amount of damaging UVC and UVB radiation on surface. (https://mars.jpl.nasa.gov/mgs/sci/fifthconf99/6128.pdf))
Melanotic bacteria increased protection for the full spectrum of UV (We want to transfer this. (https://www.sciencedirect.com/science/article/pii/S0165022X0700190X?via%3Dihub)
“melA encodes for the first step in the melanin biosynthetic pathway. it encodes a tyrosinase that catalyzes the reaction dopaquinine”.
Using the tokyo tech melA gene (https://2009.igem.org/Team:Tokyo_Tech/BlackenedEcoli#Protection_from_UV_ray) (refitted to fungi).
Melanin is a pigment and a well-known UV-protectant. It is a senseful choice both in the sense it fits our theme and furthermore it gives us a selectable genotype. By UV-irradiating the transformants vs. non-transformants it will be possible to show the effect of melanin on the growth rate/or ability to grow.
Melanin thermally stable (https://pdfs.semanticscholar.org/42b5/d1c95260addbfdf54a8632a771f16f43c40f.pdf)
Melanin (Codon optimized for A. oryzae)
(Codons is a key concept when it comes to working with fungi, and a wisely codon optimized gene for a specific species of fungi and see yield increases on heterologous genes by factors - e.g: http://www.pnas.org/content/113/41/E6117 ). Expressing the codon optimized gene alongside the original gene will show the relative expression level and thus the effect of codon optimization.
Cell wall structure and GfaA
GfaA was chosen having structural strength of the materials in mind. The structural strength fungal cells walls come from β-Glycans and Chitin, (Chitin being the most important of the two). Gfa encodes for an enzyme ??? that catalyzes the rate limiting step in the production of chitin, and overexpression. (mutants overexpressing Gfa in yeast have been shown to have I higher wall chitin content) and we theorized that overexpression of this enzyme in aspergillus oryzae might lead to a higher-than-normal Chitin content of the fungal cell walls and henceforth hopefully stronger materials
rate limiting - transferase , etc...
(http://mic.microbiologyresearch.org/content/journal/micro/10.1099/mic.0.27249-0#tab2).
Using Hph or NAT1 as a selection marker.
Colors and selectable markers - AmilCP
AmilCP is a blue Chromoprotein. We wanted to use the expression of a color protein as a “Hello World” gene. AmilCP is a blue color protein? (pigment?), and by such can be used as an easily distinguishable marker.
Mission Architecture
So how do we propose going about this entire endeavor? When a finalized version of our GMO fungi has been produced, the idea for astronauts to bring a container with our fungi spores and a container with cyanobacterium. These are brought to Mars. On their way, the astronauts will cultivate the cyanobacteria in a growing vessel, which is shaped like a long triangle. As you can see on the cross-section drawing, the vessel is a lightweight, collapsible container that can fitted with a gas pump. All the sides are zippable and on the inside, there are sown in spacers that makes the inside volume of the vessel, carve out our brick. The cyanobacteria will fill out the volume of the growing vessel while being fed CO2 through a pump, into the vessel. When the growing vessel is full with the bacterium, the astronauts will plant the GMO fungi spores onto the bacteria. After a short while the fungi will have “eaten” the cyanobacteria and taken its place, filling out the entire volume of the vessel. The astronauts can then open and start building their habitat from fully formed fungi bricks.
