Glycolate from microalgae: an efficient carbon source for biotechnological applications.

Glycolate is produced in autotrophic cells under high temperatures and C-i-limitation via oxygenation of ribulose-1,5-bisphosphate. In unicellular algae, glycolate is lost via excretion or metabolized via the C-2 cycle by consuming reductants, ATP and CO2 emission (photorespiration). Therefore, photorespiration is an inhibitory process for biomass production. However, cells can be manipulated in a way that they become glycolate-producing 'cell factories', when the ratio carboxylation/oxygenation is 2. If under these conditions the C-2 cycle is blocked, glycolate excretion becomes the only pathway of photosynthetic carbon flow. The study aims to proof the biotechnological applicability of algal-based glycolate excretion as a new biotechnological platform. It is shown that cells of Chlamydomonas can be cultivated under specific conditions to establish a constant and long-term stable glycolate excretion during the light phase. The cultures achieved a high efficiency of 82% of assimilated carbon transferred into glycolate biosynthesis without losses of function in cell vitality. Moreover, the glycolate accumulation in the medium is high enough to be directly used for microbial fermentation but does not show toxic effects to the glycolate-producing cells.