Cell wall and organelle modifications during nitrogen starvation in Nannochloropsis oceanica F&M-M24

AbstractNannochloropsis oceanica F&M-M24 is able to increase its lipid content during nitrogen starvation to more than 50% of the total biomass. We investigated the ultrastructural changes and the variation in the content of main cell biomolecules that accompany the final phase of lipid accumulation. Nitrogen starvation induced a first phase of thylakoid disruption followed by chloroplast macroautophagy and formation of lipid droplets. During this phase, the total amount of proteins decreased by one-third, while carbohydrates decreased by 12–13%, suggesting that lipid droplets were formed by remodelling of chloroplast membranes and synthesis of fatty acids from carbohydrates and amino acids. The change in mitochondrial ultrastructure suggests also that these organelles were involved in the process. The cell wall increased its thickness and changed its structure during starvation, indicating that a disruption process could be partially affected by the increase in wall thickness for biomolecules recovery from starved cells. The wall thickness in strain F&M-M24 was much lower than that observed in other strains of N. oceanica, showing a possible advantage of this strain for the purpose of biomolecules extraction. The modifications following starvation were interpreted as a response to reduction of availability of a key nutrient (nitrogen). The result is a prolonged survival in quiescence until an improvement of the environmental conditions (nutrient availability) allows the rebuilding of the photosynthetic apparatus and the full recovery of cell functions

Lactic Acid Fermentation of \u3ci\u3eArthrospira platensis\u3c/i\u3eis (Spirulina) Biomass for Probiotic-Based Products

The first objective of this study was to evaluate the use of lyophilised biomass of the cyanobacterium Arthrospira platensis F&M-C256 as the sole substrate for lactic acid fermentation by the probiotic bacterium Lactobacillus plantarum ATCC 8014. After 48 h of fermentation, the bacterial concentration was 10.6 log CFU mL−1 and lactic acid concentration reached 3.7 g L−1. Lyophilised A. platensis F&M-C256 biomass was shown to be a suitable substrate for L. plantarum ATCC 8014 growth. The second objective of the study was to investigate whether lactic acid fermentation could enhance in vitro digestibility and antioxidant activity of A. platensis biomass. Digestibility increased by 4.4%, however it was not statistically significant, while the antioxidant activity and total phenolic content did increase significantly after fermentation, by 79% and 320% respectively. This study highlights the potential of A. platensis F&M-C256 biomass as a substrate for the production of probiotic-based products