Morphological and biochemical responses of the microalga Picocystis salinarum (Chlorophyta) growing under nitrogen depletion regimes in Johnson culture medium

ABSTRACT

In response to nutritional changes, microalgae experience distinct metabolic responses, which may result in the synthesis and/or increase of certain biomolecule due to nutritional stress. The present study evaluated the morphological and biochemical responses of the microalgae Picocystis salinarum growing in Johnson culture medium under different levels of nitrogen limitation, ranging from 0,125 to 1 g L^-1 KNO₃. During cultivation, dry mass (MS), chlorophyll and carotenoids were not significantly altered in the treatments used. High nitrogen depletion (0,125 g L^-1 KNO₃) resulted in a significant increase in lipid (22,3% MS) and carbohydrate (32% MS) contents, while protein content decreased (25,3% MS). On the other hand, treatment with 0,5 g L^-1 KNO₃ revealed high values of saturated fatty acids (959,09 μg g^-1 MS) and a decrease in unsaturated fatty acids (2,56 μg g^-1 MS). The increase in lipid content was confirmed by the formation of voluminous lipid bodies, in addition to the detection of starch grains. Our results demonstrate that nitrogen depletion is a strategy to increase lipid and carbohydrate content, followed by modification of the fatty acid profile. This observation is critical for the generation of a biomass with potential biotechnological applications.

Keywords:
Algae; biomass; carbohydrates; lipids; nutritional stress