Abstract
Microalgae, due to their unique properties, gained attention for producing promising feedstocks having high contents of proteins, antioxidants, carotenoids, and terpenoids for applications in nutraceutical and pharmaceutical industries. Optimizing production of the high-value renewables (HVRs) in microalgae requires an in-depth understanding of their functional relationship of the genes involved in these metabolic pathways. In the present study, bioinformatic tools were employed for characterization of the protein-encoding genes of methyl erythritol phosphate (MEP) pathway involved in carotenoid and squalene biosynthesis based upon their conserved motif/domain organization. Our analysis demonstrates nearly 200 putative genes showing a conservation pattern within divergent microalgal lineages. Furthermore, phylogenomic studies confirm the close evolutionary proximity among these microalgal strains in the carotenoid and squalene biosynthetic pathways. Further analysis employing STRING predicts interactions among two rate-limiting genes, i.e., phytoene synthase (PSY) and farnesyl diphosphate farnesyl synthase (FPPS), which are specifically involved in the synthesis of carotenoids and squalene. Experimentally, to understand the carbon flux of these rate-limiting genes involved in carotenogenesis, an industrial potential strain, namely, Botryococcus braunii, was selected in this study for improved biomass productivity (i.e., 100 mg L–1 D–1) along with enhanced carotenoid content [0.18% dry cell weight (DCW)] when subjected to carbon supplementation. In conclusion, our approach of media engineering demonstrates that the channeling of carbon flux favors carotenogenesis rather than squalene synthesis. Henceforth, employing omics perspectives will further provide us with new insights for engineering regulatory networks for enhanced production of high-value carbon biorenewables without compromising growth.
Highlights
The rapid increase in energy consumption globally along with greenhouse gas emissions and depletion of fossil fuels has raised the requirement for the development of sustainable renewable energy sources (Davis et al, 2011; Lim et al, 2015)
This study reveals that a new approach of media engineering; i.e., carbon supplementation enhances the photosynthetic performance in microalga B. braunii, which further helps us to understand the crosstalk between different metabolic pathways involved in enhanced production of biomass, biofuels, and biorenewables (B3)
A schematic representation of methyl erythritol phosphate (MEP) biosynthetic pathway existing among microalgal lineages was illustrated (Figure 1; Kanehisa et al, 2010), depicting the presence of various functional genes involved in the carotenogenesis, facilitating better understanding of the individual components involved in the production of these high-value carbon molecules
Summary
The rapid increase in energy consumption globally along with greenhouse gas emissions and depletion of fossil fuels has raised the requirement for the development of sustainable renewable energy sources (Davis et al, 2011; Lim et al, 2015). Microalgae in due course of time emerged as a feasible alternative for biodiesel production because of their higher yields, their efficient light channeling leading to better photosynthetic efficiencies, their rapid reproduction cycles, and their ability to grow in variety of water resources (brackish, saline, and even wastewaters) (Guedes et al, 2011; Ratha and Prasanna, 2012; Abdelaziz et al, 2013; Leite et al, 2015) Other advantages include their ability to synthesize certain high-value renewables (HVRs) such as long-chain polyunsaturated fatty acids (LC-PUFAs), carotenoids such as β-carotene, astaxanthin, lutein, and isoprenoids like squalene, which are compounds of nutraceutical and pharmaceutical relevance (Spolaore et al, 2006; Raja et al, 2008). The co-production of such HVRs will further be a cost-effective addition in terms of commercial value of biodiesel production from microalgae (Dewapriya and Kim, 2014; Jutur et al, 2015)
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