Subterranean microalgae for production of microbial biomass, substances, and compositions

A method for synthesizing a product of interest, the method comprising:

• providing a culture medium comprising one or more biogenic substances and one or more minerals,
• providing a microalgal cell that produces the product of interest;
• culturing the microalgal cell in the culture medium under conditions that produce a microalgal culture comprising a plurality of microalgal cells;
• isolating the plurality of microalgal cells from the microalgal culture;
• and
• purifying the product of interest from the plurality of microalgal cells,
• wherein the product of interest is detected in a cellular capsule containing exopolysaccharide comprising rhamnose, xylose, 3-O-methyl rhamnose, glucuronic acid, galactose, glucose and mannose;
• or the product of interest is detected as a water-soluble carotenoid complex comprising astaxanthin, lutein, zeaxanthin, canthaxanthin, doradexanthin, or any combination thereof, and
• optionally wherein the synthesis of the product of interest occurs in the culture medium depleted of nitrogen and in the dark for at least a part of the culturing.