Coupling and uncoupling of triglyceride and beta-carotene production byDunaliella salinaunder nitrogen limitation and starvation.
BACKGROUND
Nitrogen starvation and limitation are known to induce important physiological changes especially in lipid metabolism of microalgae (triglycerides, membrane lipids, beta-carotene, etc.). Although little information is available forDunaliella salina, it is a promising microalga for biofuel production and biotechnological applications due to its ability to accumulate lipid together with beta-carotene.


RESULTS
Batch and chemostat experiments with various degrees of nitrogen limitation, ranging from starvation to nitrogen-replete conditions, were carried out to study carbon storage dynamics (total carbon, lipids, and beta-carotene) in steady state cultures ofD. salina. A new protocol was developed in order to manage the very high beta-carotene concentrations and to more accurately separate and quantify beta-carotene and triglycerides by chromatography. Biomass evolution was appropriately described by the Droop model on the basis of the nitrogen quota dynamics.


CONCLUSIONS
Triglycerides and beta-carotene were both strongly anti-correlated with nitrogen quota highlighting their carbon sink function in nitrogen depletion conditions. Moreover, these two valuable molecules were correlated each other for nitrogen replete conditions or moderated nitrogen limitations (N:C ratio higher than 0.04). Under nitrogen starvation, i.e., for very low N:C ratio, the dynamic revealed, for the first time, uncoupled part (higher triglyceride accumulation than beta-carotene), possibly because of shortage in key proteins involved in the stabilization of lipid droplets. This study motivates the accurate control of the microalgal nitrogen quota in order to optimize lipid productivity.
UPMC Univ Paris 06, INSU-CNRS, Laboratoire d'Océanographie de Villefranche, Sorbonne Universités, 181 Chemin du Lazaret, 06230 Villefranche-sur-mer, France ; INRIA, BIOCORE, Université Nice Côte d'Azur, 06902 Sophia Antipolis, France.
Hubert
0000-0003-0112-2512
H
Bonnefond
UPMC Univ Paris 06, INSU-CNRS, Laboratoire d'Océanographie de Villefranche, Sorbonne Universités, 181 Chemin du Lazaret, 06230 Villefranche-sur-mer, France.
Nina
N
Moelants
UPMC Univ Paris 06, INSU-CNRS, Laboratoire d'Océanographie de Villefranche, Sorbonne Universités, 181 Chemin du Lazaret, 06230 Villefranche-sur-mer, France.
Amélie
A
Talec
UPMC Univ Paris 06, INSU-CNRS, Laboratoire d'Océanographie de Villefranche, Sorbonne Universités, 181 Chemin du Lazaret, 06230 Villefranche-sur-mer, France.
Patrick
P
Mayzaud
INRIA, BIOCORE, Université Nice Côte d'Azur, 06902 Sophia Antipolis, France.
Olivier
O
Bernard
UPMC Univ Paris 06, INSU-CNRS, Laboratoire d'Océanographie de Villefranche, Sorbonne Universités, 181 Chemin du Lazaret, 06230 Villefranche-sur-mer, France ; INRIA, BIOCORE, Université Nice Côte d'Azur, 06902 Sophia Antipolis, France.
Antoine
A
Sciandra
Beta-carotene separation; Droop model; Dunaliella salina; Nitrogen starvation/limitation; Triglycerides