Abstract
Microalgae have emerged as a promising platform for production of carbon- and energy- rich molecules, notably starch and oil. Establishing an economically viable algal biotechnology sector requires a holistic understanding of algal photosynthesis, physiology, cell cycle and metabolism. Starch/oil productivity is a combined effect of their cellular content and cell division activities. Cell growth, starch and fatty acid synthesis all require carbon building blocks and a source of energy in the form of ATP and NADPH, but with a different requirement in ATP/NADPH ratio. Thus, several cellular mechanisms have been developed by microalgae to balance ATP and NADPH supply which are essentially produced by photosynthesis. Major energy management mechanisms include ATP production by the chloroplast-based cyclic electron flow and NADPH removal by water-water cycles. Furthermore, energetic coupling between chloroplast and other cellular compartments, mitochondria and peroxisome, is increasingly recognized as an important process involved in the chloroplast redox poise. Emerging literature suggests that alterations of energy management pathways affect not only cell fitness and survival, but also influence biomass content and composition. These emerging discoveries are important steps towards diverting algal photosynthetic energy to useful products for biotechnological applications.
Highlights
Microalgae are one of the most diverse eukaryotic organisms occupying wide ecological niches.By converting atmospheric CO2 to organic sugars, they provide food to many heterotrophs including humans, and participate actively in the global carbon cycle [1]
We review here latest deeper and wider molecular and genetic investigation of algal photosynthesis and metabolism
Cell division is known to be one of the most energy-consuming events during the life of a cell [12]. This is supported by the observation that when N is absent in the media, cell division/growth is arrested, and the carbon and energies harvested through an impaired photosynthesis are shunted toward starch and oil, which are accumulated in large amount in the form of starch granules and lipid droplets [76,77]
Summary
Microalgae are one of the most diverse eukaryotic organisms occupying wide ecological niches. Global outputs of photosynthesis are triose phosphate (i.e., glyceraldehyde 3-phosphate (GA3P)), reducing equivalents (NADPH) and phosphorylating power (ATP), which constitutes the major metabolic intermediates in a cell. These three compounds are essential to support all activities in a cell, i.e., cell division, growth, and reserve accumulation (Figure 1). Microalgae having impaired energy2.sinks (starch signal(s) that connect the demand (sink) to activity the production site (photosynthetic chain, source) are not or oil) usually show lower photosynthetic [8,9]. Microalgae impaired production energy sinks (starch and or ATP, oil) or usually show metabolic demand governshaving the photosynthetic of NADPH if it works thelower other photosynthetic way around. Conditions, which are relevant to large scale cultivation [19]
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