CO2 and Oxygen Sensors and Measuring Cell Respiration

Everyone knows that people breathe in oxygen and exhale carbon dioxide, but how do you directly measure respiration at the cellular level? This was part of the problem faced by Dr. Nikolai Slavov and his team from the Departments of Physics and Biology and Koch Institute for Integrative Cancer Research at the Massachusetts Institute of Technology.

Using the ESCM-54 iSense CO2 and Oxygen Monitor and Data Logger, the team was able to accurately measure the absolute rates of O2 uptake and CO2 synthesis in yeast cells as they both respire and ferment simultaneously. The data lead to the discovery that cell metabolism and physiology can vary, even as growth rates remains constant. Their results were published in a recent paper titled, “Constant Growth Rate Can Be Supported by Decreasing Energy Flux and Increasing Aerobic Glycolysis.

To create the test, Slavov developed a sealed bioreactor that housed batches of yeast cells. A constant rate of air was fed into the bioreactor. The levels of oxygen and carbon dioxide in the closed-loop system were measured by the iSense over time. This setup allowed estimating the absolute rates of respiration and fermentation using only direct measurements and mass conservation. It allows much more direct and time resolved measurements than other systems used previously for measuring the fluxes of O2 and CO2.

“Direct measurements were essential,” according to Dr. Slavov. “We wanted to directly detect and quantify carbon dioxide and oxygen, not their surrogates, such as changes in pH and fluoresce of oxygen-binding fluorophores.”

As a result of these experiments, science now has a better understanding of cell growth essential to both basic science and treating diseases associated with deregulated cell growth, such as cancer.

Nikolai Slavov is a Fellow in the Departments of Biology and Physics at MIT and the Department of Statistics and FAS Systems Biology Center at Harvard.