What this work is about, in plain words
A review of how cyanobacteria, including spirulina, obtain carbon for growth from carbon dioxide and dissolved salts. The authors propose a generalized scheme of these pathways for spirulina.
Carbon is the main building material of the cell. In water it occurs in three forms — dissolved carbon dioxide, bicarbonate ions and carbonate ions — and their ratio depends on the acidity of the medium. If the form the cell needs is in short supply, culture growth slows down. The authors summarized how cyanobacteria take up and fix inorganic carbon.
The work is a review: it covers published data on the so-called carbon-concentrating mechanism. With it, the cell accumulates carbon inside, mainly as bicarbonate, and reduces its losses.
In the authors' assessment, it is this mechanism that allows microalgae and cyanobacteria to photosynthesize at the same maximum rate at both low and high CO₂ concentrations. Most studies were done on cells with a nucleus, where carbon can accumulate in different parts of the cell. In cyanobacteria the mechanism works differently. Based on current understanding, the authors propose a generalized scheme of carbon pathways for spirulina (Arthrospira platensis).
Understanding these pathways helps in choosing the form in which to supply carbon to a culture, for example replacing CO₂ supply with bicarbonate.
Limitations. This is a short literature review: it contains no new experimental data, and the proposed scheme summarizes published information.