Abstract
Thalassiosira pseudonana is a transformable and biotechnologically promising model diatom with an ability to synthesise nutraceuticals such as fucoxanthin and store a significant amount of polyglucans and lipids including omega-3 fatty acids. While it was the first diatom to be sequenced, a systems-level analysis of its metabolism has not been done yet. This work presents first comprehensive, compartmentalized, and functional genome-scale metabolic model of the marine diatom Thalassiosira pseudonana CCMP 1335, which we have termed iThaps987. The model includes 987 genes, 2477 reactions, and 2456 metabolites. Comparison with the model of another diatom Phaeodactylum tricornutum revealed presence of 183 unique enzymes (belonging primarily to amino acid, carbohydrate, and lipid metabolism) in iThaps987. Model simulations showed a typical C3-type photosynthetic carbon fixation and suggested a preference of violaxanthin–diadinoxanthin pathway over violaxanthin–neoxanthin pathway for the production of fucoxanthin. Linear electron flow was found be active and cyclic electron flow was inactive under normal phototrophic conditions (unlike green algae and plants), validating the model predictions with previous reports. Investigation of the model for the potential of Thalassiosira pseudonana CCMP 1335 to produce other industrially useful compounds suggest iso-butanol as a foreign compound that can be synthesized by a single-gene addition. This work provides novel insights about the metabolism and potential of the organism and will be helpful to further investigate its metabolism and devise metabolic engineering strategies for the production of various compounds.
Highlights
Diatoms are unique unicellular photosynthetic eukaryotic microbes that have silica incorporated in their cell wall [1]
We have evaluated the effect of variation of Non growth-associated ATP maintenance (NGAM) on intracellular flux distributions
The draft model was subjected to manual gap finding analysis, which identified only 62 orphan enzymes required for biomass-precursor biosynthesis
Summary
Diatoms are unique unicellular photosynthetic eukaryotic microbes that have silica incorporated in their cell wall [1] They play a significant role in global carbon and silicon recycling [1] and contribute about half of aquatic primary production and a quarter of the total primary productivity [2]. Diatoms primarily store glucose in the form chrysolaminarin [6], a polyglucan (primarily composed of β(1→3) linked glucose monomers) which can be used as renewable feedstock for fermentation and subsequent production of platform chemicals Their ability to store a significant amount of lipids (20–30% and in some species up to 45–60% of the dry cell weight) [7] and synthesize nutraceuticals such as omega-3 fatty acids [7,8] and fucoxanthins [3,9] makes them attractive organisms. The work focuses on the potential of T. pseudonana to photosynthetically produce some industrially useful compounds
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