Abstract
BackgroundMicroalgae have been proposed as potential platform to produce lipid-derived products, such as biofuels. Knowledge on the intracellular carbon flow distribution may identify key metabolic processes during lipid synthesis thus refining culture/genetic strategies to maximize cell lipid productivity. A kinetic metabolic model simulating cell metabolic behavior and lipid production was first applied in the microalgae platform Chlorella protothecoides under heterotrophic condition. It combines both physiology and flux information in a kinetic approach. Cell nutrition, growth, lipid production and almost 30 metabolic intermediates covering central carbon metabolism were included and simulated.ResultsModel simulations were shown to adequately agree with experimental data, which is suggesting that the proposed model copes with Chlorella protothecoides cells’ biology. The dynamic metabolic flux analysis using the model showed a reversible starch flux from accumulation to decomposing when glucose reached depletion, while net lipid flux shows a quasi-constant rate. The sensitive flux parameters on starch and lipid metabolism suggested that starch synthesis is the major competing pathway that affects lipid accumulation in C. protothecoides. Flux analysis also demonstrated that high lipid yield under heterotrophic condition is accompanied with high lipid flux and low TCA activity. Meanwhile, the dynamic flux distribution also suggests a relatively constant ratio of glucose distributed to biomass, lipid, starch, nucleotides as well as pentose phosphate pathway.ConclusionThe model described not only experimental data, but also unraveled intracellular carbon flow distribution and identify key metabolic processes during lipid synthesis. Most of the metabolic kinetics also showed statistical significance for metabolic mechanism. Therefore, this study unravels the mechanisms of the glucose impact on the dynamic carbon flux distribution, thus improving our understanding of the links between carbon fluxes and lipid metabolism in C. protothecoides.
Highlights
Microalgae have been proposed as potential platform to produce lipid-derived products, such as biofuels
An underestimated potential output of these kinetic metabolic models relies in their capacity to perform dynamic metabolic flux analysis from which key metabolic processes can be examined while assessing in silico hypothesis of genetic engineering and/or culture conditions management strategies [17]
The sensitive flux parameters on starch and lipid metabolism suggested that starch synthesis is the major competing pathway that affect lipid accumulation in C. protothecoides
Summary
Microalgae have been proposed as potential platform to produce lipid-derived products, such as biofuels. A kinetic metabolic model simulating cell meta‐ bolic behavior and lipid production was first applied in the microalgae platform Chlorella protothecoides under hetero‐ trophic condition. It combines both physiology and flux information in a kinetic approach. In Chlorella sp., a shift in intracellular flux distribution was predicted during transition from nutrient sufficient phase to nutrient starvation phase of growth [14]. Another appealing modeling approach, which allows simulating a culture’s dynamics, is based on a kinetic transient-type approach [15, 16]. There are very few studies reporting dynamic metabolomics data of microalgae and even less on the development of mathematical models to describe cell metabolic dynamics [18]
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