An iGEM classic, bioreactors are crucial to synthetic biology projects, providing and optimizing bacterial growth to increase wet lab stock and decreasing costs. This year, we built two bioreactors tailored towards our two chassis, C. crescentus and S. Elongatus. Our research questions for these two bioreactors explores the characteristics of each and how they affect our bioreactors’ conditions.
An Introduction to Bioreactors
What is a Bioreactor?
Various types of bacteria can have a wide variety of applications, from producing medicines, foods such as cheese, and biobricks, as our project aims to do. Due to the many processes that require some form of bacteria to fabricate an end product, there must be resources delegated to ensuring there is always a steady supply of bacteria.
A bioreactor is a vessel which is able to control different environmental factors, such that you would be able to control the conditions that affect a biological process within a vessel. The use of a bioreactor would allow for the optimization of growth conditions by use of a series of sensors and controllers to measure and adjust internal conditions. This optimal environment would require the bioreactor to consider the light levels that come into contact with the bacteria ([1]). On top of this, certain light intensities will have different impacts on the bacterial growth, as will the wavelength. Furthermore, the pH and temperature of a solution are two more environmental considerations that a bioreactor should aim to stabilize. Another factor that is seen in a wide variety of bioreactors is the ability to aerate and agitate bacteria within itself to further promote growth ([2]).
How does it assist Wet Lab?
Our team’s wet lab uses multiple different strains of bacteria for the purpose of conducting experiments to help optimize surface expression and growth media. Many of these experiments involve the use of different bacterial strains, including Caulobacter crescentus CB2A and Synechococcus elongatus UTEX 2973, and it is important to be able to have a consistent flow of these bacteria for any of these projects.
The caulobacter strain being used, Caulobacter crescentus CB2A (CB2A), has particularly long growth times, which would require wet lab personnel to spend upwards of 10 hours within a lab in order to complete a single growth curve. This demonstrates a problem with the amount of time and resources that are needed in order to continuously grow CB2A strains for experiments. The use of a bioreactor aims to fix this by optimizing the growth conditions for the bacterial strain. This would, in turn, lengthen the exponential growth time of the strain, leading to overall shorter times needed to produce one growth curve. This allows our wet lab members to have significantly more time cleared up, which would allow them to work more effectively on other experiments.
The other main strain that is being used is Synechoccoccus elongatus UTEX 2973 (UTEX), and this strain tends to be quite difficult to use. Furthermore, a large amount of the bacteria is generally needed for the experiments that we have been running with them. Due to this, it is common for multiple experiments to be run to receive one result. This leads to the amount of cyanobacteria that is used in our wet lab team being quite large, meaning that there has to be a quick production of the bacteria to allow experiments to be done more quickly. Bioreactors can also be built for this, as growth curves would take significantly less time, meaning that there would be a much larger total flow of UTEX going into the wet lab to allow them to keep running experiments.
How can it be applied in the context of our Space Mission?
The breakthrough that we plan to make as a design team looking into space construction is to make a sustainable solution to give future Mars colonies the resources to make a variety of buildings through the use of biocement. For this to be possible, we must ensure that all the materials required for making an effective biocement are available on an extraterrestrial work site such that there is enough to reasonably support any potential construction project. One of the key factors of this biocement production is UTEX, as it is a bacterium that can crosslink with itself, resulting in sturdy bricks. With this need for UTEX as a crucial material to our biocement, it is important to ensure that we are able to grow bacteria on site and quickly enough to be an effective source of UTEX.
A bioreactor is an effective tool for this, as its purpose is to create an environment that is optimal for the quick production of a given bacterium. If it is capable of taking some UTEX and running an efficient growth curve, there could be a steady flow of bacteria to be used for additional constructions. This is a far better alternative than launching building materials from earth due to the tremendous amount of money and resources that would be required for this method to send a useful amount of construction materials. With this alternative solution using a bioreactor, there would only need to be one initial successful shipment of bioreactors and bacteria, which would then be able to consistently and sustainably grow new bricks.
One factor that does not typically need to be considered for bioreactors being used in Earth applications is gravity changes. Gravity tends to be relatively similar at any point on the Earth, around 9.8 m/s^2. This roughly constant value must be considered for any space applications, though, as celestial masses with different radii and masses will generally have different gravitational fields. This is no different for Mars, a planet with a surface gravity of around 3.73 m/s^2. Standard bioreactors do not have a way of measuring a lower or higher gravity on their own; however, this is an important factor to test for when considering the growth of bacteria. As such, a bioreactor must be designed to simulate lower gravity conditions. Without the construction of a bioreactor for this purpose, it would not be possible to tell how UTEX 2973 would be able to grow in low-gravity conditions.
Main Takeaways from Our Bioreactor Efforts from Last Year
The bioreactors that were used last year were able to show improvements in the speed at which bacteria were grown. This is what a bioreactor should do with this application, and these bioreactors were able to troubleshoot through a variety of problems that came up during production. These takeaways will be considered for the new group of bioreactors coming for the 2025 season.
For any wet lab procedure, it is important to be able to effectively sterilize the surfaces that come into contact with any materials that are required for the study. Any contamination would potentially affect the growth curves that are done with bioreactors. This is something that should be considered in any bioreactor design, and it is one of the qualities of this year’s bioreactors that will be planned around. To accommodate this, we want to ensure that it is possible and reasonable to use an autoclave on all important locations that may come into direct contact with a growth medium and various experiments. This must be done while also ensuring that any piece of the bioreactor that is not capable of being autoclaved would not receive any damage in the process of sterilization of other sections of the product.
Additionally, the bioreactors of this year should aim to be easy to use and work autonomously. During design, it must be factored in that any product that is made should aim to be functional, but also be reasonably easy to use, so individuals working in a lab do not need to monitor it too much. This would go against the goals of this project, and as such, the bioreactors of this year should be fitted with automated processes for detecting changes in the environment, as well as any adjustments. It would be optimal for all of their processes to work through a system that allows for remote use.
We will aim towards optimizing our bioreactors for our chassis and researching the impact of agitation on Caulobacter and its biofilm as well as the impact of light type and wavelength on Synechococcus growth.
