Subcellular Energetics and Carbon Storage in Chlamydomonas

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.

The Aureochrome Photoreceptor PtAUREO1a Is a Highly Effective Blue Light Switch in Diatoms

“…Light acclimation has been studied intensively in diatoms, showing that a shift from low to high light induces a reduction in light harvesting antenna size, and an increase of components of electron transport and C-assimilation, but also leads to higher activities of photoprotection, N-assimilation, protein biosynthesis, carbohydrate storage, nutrient transporters, and cell proliferation ( Smith et al., 2019 ; Wilhelm et al., 2014 ). In green algae, the mechanism triggering this cellular reorganization is closely linked to the light-dependent redox state of the cells (reviewed in Burlacot et al., 2019 ). In diatoms, the redox state of the PQ pool is also involved in light acclimation reactions ( Lepetit et al., 2013 ), but the redox control machinery in the plastid via the redox regulator thioredoxin is different from that of green algae ( Matsuda and Kroth, 2014 ).…”

Elimination of the flavodiiron electron sink facilitates long-term H2 photoproduction in green algae

“…The direct pathway involves photosystem (PS) II-dependent water photolysis [13]. The indirect pathway bypasses PSII, feeding [FeFe]-hydrogenases with electrons originating from starch, protein or lipid breakdown and arriving at the PQ pool via NADPH-dehydrogenase (NDA2) [14, 15]. The third pathway, named as fermentative pathway, functions under dark anaerobic conditions and involves electron transfer via a pyruvate–ferredoxin-oxidoreductase from pyruvate to the [FeFe]-hydrogenase [16, 17].…”

CO2supply modulates lipid remodelling, photosynthetic and respiratory activities inChlorellaspecies

“…The differential response in lipid classes in the two strains to high CO 2 level is further supported by fatty acid compositional alterations. Among other reasons, lipid compositional changes are mostly likely results of altered redox status brought about by differential chloroplast and mitochondrial energetic activities in response to varying CO 2 availability in the two Chlorella genus (Figure 6, Figure 8) (Burlacot et al, 2019).…”