Simultaneous accumulation of lipid and carotenoid in freshwater green microalgae Desmodesmus subspicatus LC172266 by nutrient replete strategy under mixotrophic condition

Bioactive compounds by microalgae and potentials for the management of some human disease conditions

Microalgae biomasses are excellent sources of diverse bioactive compounds such as lipids, polysaccharides, carotenoids, vitamins, phenolics and phycobiliproteins. Large-scale production of these bioactive substances would require microalgae cultivation either in open-culture systems or closed-culture systems. Some of these bioactive compounds (such as polysaccharides, phycobiliproteins and lipids) are produced during their active growth phase. They appear to have antibacterial, antifungal, antiviral, antioxidative, anticancer, neuroprotective and chemo-preventive activities. These properties confer on microalgae the potential for use in the treatment and/or management of several neurologic and cell dysfunction-related disease conditions, including Alzheimer's disease (AD), AIDS and COVID-19, as shown in this review. Although several health benefits have been highlighted, there appears to be a consensus in the literature that the field of microalgae is still fledgling, and more research needs to be carried out to ascertain the mechanisms of action that underpin the effectiveness of microalgal compounds. In this review, two biosynthetic pathways were modeled to help elucidate the mode of action of the bioactive compounds from microalgae and their products. These are carotenoid and phycobilin proteins biosynthetic pathways. The education of the public on the importance of microalgae backed with empirical scientific evidence will go a long way to ensure that the benefits from research investigations are quickly rolled out. The potential application of these microalgae to some human disease conditions was highlighted.

Effects of organic carbon sources on growth and oil accumulation by Desmodesmus subspicatus LC172266 under mixotrophic condition

Energy crisis and environmental sustainability have attracted global attention to microalgal biofuels. The present study investigated the impact of organic carbon sources on growth and bio-oil accumulation by an oleaginous microalga Desmodesmus subspicatus LC172266 under mixotrophic culture condition. Glucose and glycerol supported higher growth rates and lipid productivities than sucrose, fructose, mannitol and acetate. Each of the organic carbon source tested supported significantly (P < 0.05) higher growth rates and lipid productivities than the photoautotrophic culture (without organic carbon source). The lipid productivity obtained with a mixture of optima concentrations of glucose and glycerol (5.0 gL^-1 glycerol + 10.0 gL^-1glucose) (0.14875 ± 0.002 g/L/day) was about 25% and 66% higher than the values obtained with only 10.0 gL^-1glucose and 5.0 gL^-1glycerol, respectively. When a batch culture with 5gL^-1glycerol was fed with 0.5 gL^-1glucose daily the cell growth and lipid productivity were lower than the values obtained in a batch culture with a mixture of glucose and glycerol. The lipid productivity obtained in a 4-L photobioreactor was 94% (0.217 gL^-1 day^-1), higher than the value obtained in a flask culture with 10.0 g/Lglucose (0.112 gL^-1 day^-1) and 46% higher than the value obtained in a flask culture with 5.0 gL^-1glycerol (0.086 gL^-1 day^-1).

A comprehensive review on carbon source effect of microalgae lipid accumulation for biofuel production

Energy is a major driving force for the economic development. Due to the scarcity of fossil fuels and negative impact on the environment, it is important to develop renewable and sustainable energy sources for humankind. Microalgae as the primary feedstock for biodiesel has shown great application potential. However, lipid yield from microalgae is limited by the upstream cost, which restrain the realization of large-scale biofuel production. The modification of lipid-rich microalgae cell has become the focus over the last few decades to improve the lipid content and productivity of microalgae. Carbon is a vital nutrient that regulates the growth and metabolism of microalgae. Different carbon sources are assimilated by microalgae cells via different pathways. Inorganic carbon sources are mainly used through the CO₂-concentrating mechanisms (CCMs), while organic carbon sources are absorbed by microalgae mainly through the Pentose Phosphate (PPP) Pathway and the Embden-Meyerhof-Pranas (EMP) pathway. Therefore, the addition of carbon source has a significant impact on the production of microalgae biomass and lipid accumulation. In this paper, mechanisms of lipid synthesis and carbon uptake of microalgae were introduced, and the effects of different carbon conditions (types, concentrations, and addition methods) on lipid accumulation in microalgal biomass production and biodiesel production were comprehensively discussed. This review also highlights the recent advances in microalgae lipid cultivation with large-scale commercialization and the development prospects of biodiesel production. Current challenges and constructive suggestions are proposed on cost-benefit concerns in large-scale production of microalgae biodiesel.

Recent advancements in mixotrophic bioprocessing for production of high value microalgal products

Recently, microalgal biomass has become an attractive and sustainable feedstock for renewable production of various biochemicals and biofuels. However, attaining required productivity remains a key challenge to develop industrial applications. Fortunately, mixotrophic cultivation strategy (MCS) is leading to higher productivity due to the metabolic ability of some microalgal strain to utilise both photosynthesis and organic carbon compared to phototrophic or heterotrophic processes. The potential of MCS is being explored by researchers for maximized biochemicals and biofuels production however it requires further development yet to reach commercialization stage. In this review, recent developments in the MCS bioprocess for selective value-added (carotenoids) products have been reviewed; synergistic mechanism of carbon and energy was conferred. Moreover, the metabolic regulation of microalgae under MCS for utilized carbon forms and carbon recycling was demonstrated; Additionally, the opportunities and challenges of large-scale MCS have been discussed.