What this work is about, in plain words
Why does a spirulina culture stop growing although about half of the carbon still remains in the medium? The authors explained this with a mathematical model linking growth to the acidity of the medium.
Spirulina is often grown in batches on a medium with a supply of soda and without external carbon dioxide. In such experiments, culture growth stops even though about half of the added carbon and other nutrients still remain in the medium. The authors set out to explain this phenomenon.
The authors built a mathematical model of the growth of an Arthrospira (Spirulina) platensis culture in a carbon-closed system. The model is based on established ideas about how the cell takes up carbon from the medium and uses it.
According to the authors' model, while the culture grows quickly, the cells take bicarbonate from the medium, and the medium becomes more and more alkaline. The concentration of hydroxyl ions rises exponentially, and bicarbonate declines. At high alkalinity, the remaining carbon passes into a form that is poorly available to the cells, and growth stops. The model describes experimental data well during fast growth and explains fluctuations in culture density after growth stops.
The work helps to understand why the acidity of the medium and the carbon supply must be controlled for dense spirulina cultures.
Limitations. This is a model for a system without external carbon supply. It was tested on laboratory data and is most accurate during fast growth.