Quantification of extracellular and biomass carbohydrates by Arthrospira under nitrogen starvation at lab-scale

Abstract

Nitrogen starvation is known to stimulate the production of carbohydrates in Arthrospira. This study aimed to investigate the relative importance of extracellular (released in culture medium, loosely bound to the cell) versus biomass carbohydrates (cell wall, cytoplasmic). Nitrogen (N) starvation did not result in a lower trichome production (as evaluated from optical density, trichome biovolume, and DNA concentration) compared to N-repleted conditions up to 10 days after N was depleted from the culture medium. The dry weight biomass production was even higher under N starvation, which can be attributed to an increase in the specific density of the biomass due to the accumulation of glycogen. Nitrogen starvation resulted in a strong increase in intracellular and cell wall carbohydrates, a moderate increase in loosely bound extracellular carbohydrates but did not affect released carbohydrates, at least not up to 10 days after N was depleted from the culture medium. Specifically, carbohydrates in the biomass reached 688 mg g−1. Enzymatic hydrolysis of the biomass with amyloglucosidase showed that 82 % of the biomass carbohydrates could be converted to glucose and, hence, consisted of glycogen. We also detected substantial amounts of the dissolved disaccharide trehalose (19.86 mg g−1) in N-starved Arthrospira. The carbohydrates accumulated in Arthrospira biomass under N starvation may be used as feedstock for biofuels or building blocks for the chemical industry.