Channeling of Carbon Flux Towards Carotenogenesis in Botryococcus braunii: A Media Engineering Perspective

Dynamic metabolomic crosstalk between Chlorella saccharophila and its new symbiotic bacteria enhances lutein production in microalga without compromising its biomass

The microalgae Chlorella saccharophila UTEX247 was co-cultured with its symbiotic indigenous isolated bacterial strain, Exiguobacterium sp., to determine the possible effects of bacteria on microalgae growth and lutein productivity. Under optimal conditions, the lutein productivity of co-culture was 298.97 µg L-1 d-1, which was nearly 1.45-fold higher compared to monocultures i.e., 103.3 µg L-1 d-1. The highest lutein productivities were obtained in co-cultures, accompanied by a significant increase in cell biomass up to 0.84-fold. These conditions were analyzed using an untargeted metabolomics approach to identify metabolites enhancing valuable renewables, i.e., lutein, without compromising growth. Our qualitative metabolomic analysis identified nearly 30 (microalgae alone), 41 (bacteria alone), and 75 (co-cultures) metabolites, respectively. Among these, 46 metabolites were unique in the co-culture alone. The co-culture interactions significantly altered the role of metabolites such as thiamine precursors, reactive sugar anomers like furanose and branched-chain amino acids (BCAA). Nevertheless, the central metabolism cycle upregulation depicted increased availability of carbon skeletons, leading to increased cell biomass and pigments. In conclusion, the co-cultures induce the production of relevant metabolites which regulate growth and lutein simultaneously in C. saccharophila UTEX247, which paves the way for a new perspective in microalgal biorefineries.

Multi-Fold Enhancement of Tocopherol Yields Employing High CO2 Supplementation and Nitrate Limitation in Native Isolate Monoraphidium sp

Tocopherols are the highly active form of the antioxidant molecules involved in scavenging of free radicals and protect the cell membranes from reactive oxygen species (ROS). In the present study, we focused on employing carbon supplementation with varying nitrate concentrations to enhance the total tocopherol yields in the native isolate Monoraphidium sp. CABeR41. The total tocopherol productivity of NRHC (Nitrate replete + 3% CO2) supplemented was (306.14 µg·L−1 d−1) which was nearly 2.5-fold higher compared to NRVLC (Nitrate replete + 0.03% CO2) (60.35 µg·L−1 d−1). The best tocopherol productivities were obtained in the NLHC (Nitrate limited + 3% CO2) supplemented cells (734.38 µg·L−1 d−1) accompanied by a significant increase in cell biomass (2.65-fold) and total lipids (6.25-fold). Further, global metabolomics using gas chromatography-mass spectrometry (GC-MS) was done in the defined conditions to elucidate the molecular mechanism during tocopherol accumulation. In the present study, the Monoraphidium sp. responded to nitrogen limitation by increase in nitrogen assimilation, with significant upregulation in gamma-Aminobutyric acid (GABA). Moreover, the tricarboxylic acid (TCA) cycle upregulation depicted increased availability of carbon skeletons and reducing power, which is leading to increased biomass yields along with the other biocommodities. In conclusion, our study depicts valorization of carbon dioxide as a cost-effective alternative for the enhancement of biomass along with tocopherols and other concomitant products like lipids and carotenoids in the indigenous strain Monoraphidium sp., as an industrial potential strain with relevance in nutraceuticals and pharmaceuticals.

A Fast-Growing Oleaginous Strain of Coelastrella Capable of Astaxanthin and Canthaxanthin Accumulation in Phototrophy and Heterotrophy

Considering the importance of microalgae as a promising feedstock for the production of both low- and high-value products, such as lipids and pigments, it is desirable to isolate strains which simultaneously accumulate these two types of products and grow in various conditions in order to widen their biotechnological applicability. A novel freshwater strain from the genus Coelastrella was isolated in Belgium. Compared to other Coelastrella species, the isolate presented rapid growth in phototrophy, dividing 3.5 times per day at a light intensity of 400 µmol·m⁻²·s⁻¹ and 5% CO₂. In addition, nitrogen depletion was associated with the accumulation of astaxanthin, canthaxanthin, and fatty acids, which reached ~30% of dry weight, and a majority of SFAs and MUFAs, which are good precursors for biodiesel. This strain also accumulated astaxanthin and canthaxanthin in heterotrophy. Although the content was very low in this latter condition, it is an interesting feature considering the biotechnological potential of the microalgal heterotrophic growth. Thus, due to its rapid growth in the light, its carotenogenesis, and its fatty acids characteristics, the newly identified Coelastrella strain could be considered as a potential candidate for biorefinery purposes of both low- and high-values products.