BIOTECHNOLOGY - V. H. Herasymenko - 2006

Part II. Special Biotechnologies

Chapter 24. BIOTECHNOLOGY FOR THE PRODUCTION OF BIOMASS OF THE UNICELLULAR ALGA SPIRULINA

24.2. COMPOSITION OF THE NUTRIENT MEDIUM FOR SPIRULINA CULTIVATION

Spirulina is a fastidious phototrophic cyanobacterium that requires a balanced nutrient medium for growth, which must necessarily include such biogenic elements as carbon, nitrogen, phosphorus, sulfur, magnesium, sodium, potassium, and iron. Of particular importance is the nitrogen concentration in the medium.

Carbon. Unlike terrestrial plants, which can only access atmospheric CO₂, Algae can utilize H₂CO₃ (carbonic acid) and its ions—bicarbonate (HCO₃^_) and carbonate (CO₃^2-). This depends on pH, Water salinity, atmospheric partial pressure of CO₂, and ambient Temperature. Carbon dioxide (CO₂) dominates in acidic solutions, but its influence drops sharply at pH 7–9, where bicarbonate (HCO₃^_) prevails, while in more alkaline environments, the CO₃^2- anion begins to play a crucial role.

Alongside carbon, algae utilize hydrogen, oxygen, phosphorus, and nitrogen to synthesize organic matter.

Nitrogen. Spirulina can assimilate nitrogen in three forms: gaseous, as Inorganic Compounds, and as biopolymer nitrogen. The ability to fix gaseous nitrogen is found exclusively in prokaryotes, to which Spirulina belongs. Mineral compounds utilized include nitrate (NO₃^_), nitrite (NO₂^_), and ammonium (NH₄⁺) ions.

Phosphorus is essential for Spirulina Cells to synthesize Nucleic Acids, Phospholipids, and phosphoric acid esters. The sole natural source of inorganic phosphorus for Spirulina is orthophosphates. Blue-green algae are capable of accumulating excess phosphorus in the form of granules.

In algae growing under optimal supply conditions, The ratio of the three main biogenic elements C:N:P is 106:16:1. This ratio is known as the Redfield ratio (Redfield et al., 1963). However, algal populations can also develop at N:P ratios ranging from 5:1 to 15:1.

Spirulina's Mineral Requirements are met by macro- and microelement salts. For artificial cultivation, standard Tamiya, Zarrouk, or Gromov nutrient media are used. The Tamiya medium relies on magnesium and potassium compounds, the Gromov medium contains predominantly sodium and magnesium compounds, whereas the Zarrouk medium, which is most widely used, contains a significant amount of sodium bicarbonate (16.8 g/L), maintaining a pH around 9.5.

Spirulina feeding types. The algal metabolic processes are supported by three Types of Nutrition: autotrophic, heterotrophic, and mixotrophic.

Under conditions of intense illumination and optimal thermal regimes, autotrophic nutrition prevails in Spirulina. In this case, photosynthetic processes occur utilizing mineral elements and carbon dioxide (CO₂) directly from the nutrient medium.

Under heterotrophic nutrition, part of the energy can be derived from the assimilation and oxidation of CARBOHYDRATES and other Organic compounds. These processes take place primarily in the dark. The third type of nutrition combines both autotrophic and heterotrophic metabolic processes.

Industrial technology for Spirulina biomass production focuses on autotrophic nutrition, meaning the culture is grown on a mineral medium. When industrial wastes from alcohol, sugar, and other industries are added to the nutrient medium, cultivation proceeds under heterotrophic conditions. Instead of carbon dioxide, the carbon from organic compounds—such as sugars, alcohols, and organic — will be utilized.

acids. Heterotrophic nutrition can also occur under alternating light and dark conditions.