RWV-HARV Bioreactor (Rotating Wall Vessel- High Aspect Ratio Vessel Bioreactor)
To bioengineer AstroYeast, we require a bioreactor and a microgravity simulator to execute our experiments. The microgravity we are aiming to simulate is known as Low Shear Simulated Microgravity (LSSMG) which creates microgravity conditions of 10-3 - 10-6 g (Huang, Li, and Huang, 2018) Microgravity conditions on the International Space Station are 10-5 - 10-6 g, nonetheless LSSMG is accepted in the microgravity research community as a suitable analog to space. As we are performing adaptive evolution, we require a safe environment in which the cells can grow for an extended duration of time, creating the need for a bioreactor which circulates nutrients and removes cellular waste products.
The principle behind microgravity simulation is to cancel the vector of gravity acting on cells, so that the net gravity felt by the cell is as close to zero as possible. In a rotating wall vessel, the cells are suspended in liquid media with as much gas removed as possible. As the vessel rotates, the cells naturally fall through the media due to Earth’s gravity. The rotation provides an acceleration vector which keeps the cells in continuous free fall, or microgravity conditions (Klaus, 2001). This concept is analogous to how the International Space Station orbits Earth. The vectors felt by the cell are averaged to zero faster than the biological processes monitored (Klaus, 2001). Microgravity simulators are generally used as a precursor to sending experiments into space, as the same experiment can first be performed here on Earth at a fraction of the cost.
The above figure demonstrates how a rotating wall vessel simulates microgravity (Yamaguchi et al., 2014).
The bioreactor creates an ideal environment for the yeast to culture and grow, while minimizing agitation. This includes nutrients and oxygen supply, removal of cellular waste and temperature control.
Why a High Aspect Ratio Vessel (HARV)?
For our microgravity simulator we have chosen a High Aspect Ratio Vessel (HARV), which is a version of the Rotating Wall Vessel (RWV) first developed by NASA for microgravity studies. The HARV was selected as it is used amongst established microgravity yeast researchers, such as Dr. Corey Nislow who has launched yeast studies to the ISS multiple times. We have integrated a bioreactor into our HARV design. It consists of a cylinder bioreactor rotating horizontally along a single axis of rotation with gas, oxygen, nutrient and waste exchange across a membrane.
Huang, B., Li, D., Huang, Y. et al. Effects of spaceflight and simulated microgravity on microbial growth and secondary metabolism. Military Med Res 5, 18 (2018). Doi: link
Klaus D. M. (2001). Clinostats and bioreactors. Gravitational and space biology bulletin : publication of the American Society for Gravitational and Space Biology, 14 (2), 55–64. PMID: 11865869
Yamaguchi, N., Roberts, M., Castro, S., Oubre, C., Makimura, K., Leys, N., Grohmann, E., Sugita, T., Ichijo, T., & Nasu, M. (2014). Microbial monitoring of crewed habitats in space-current status and future perspectives. Microbes and environments, 29(3), 250–260. https://doi.org/10.1264/jsme2.me14031