org/10.1016/j.cbpa.2013.02.027 Improving the productivity of strains is a major factor in making algal biofuels economically viable [1••]. Algal productivity is ultimately dependent
on the efficiency of carbon fixation and the downstream cellular processes that convert photosynthate into useful fuel precursors. The diversity of contemporary microalgal metabolism has been shaped by multiple endosymbiotic acquisitions, environmental factors, and evolutionary selection. The result has been distinct intracellular compartmentation Talazoparib ic50 and unique organizational schemes among different algal classes [2••], especially in relation to the location of carbon fixation enzymes and carbohydrate storage (Figure 1). Organizational differences likely affect processes such as photosynthesis, carbon flux through metabolic networks, and biosynthesis of fuel-relevant compounds. The goal of this review is to highlight the
relevance of these aspects of algal diversity to biofuel molecule production. The evolution of microalgae has generated a variety of components and organizational schemes of the photosynthetic apparatus (Figure 2). All microalgae have light harvesting antenna complexes, PSII, the cytochrome b6f complex, and PSI. The use of the bulky phycobilisomes (peripherally Ibrutinib molecular weight associated with the thylakoid membrane) for light harvesting in cyanobacteria, glaucophytes, PRKACG and rhodophytes results in a relatively large spacing between the photosynthetic membranes (Figure 2a and c), which could affect photosynthetic capacity [3]. Downsizing of the light harvesting complexes is apparent in rhodophytes, which have membrane-integral LHCs, and cryptomonads, which utilize unassembled biliproteins in the lumen of the thylakoids, enabling stacked thylakoid grana (Figure 2). Stacked grana arose independently in both chlorophytes and in derivatives of the red algae, and may serve to enhance light
capture and connectivity between PSIIs with large functional antenna size [3 and 4]. The numbers of grana stacks differ; chromalveolates typically have three, while chlorophytes can have 2–3 times more [5•]. In chlorophytes, PSII is highly enriched in the grana and PSI in the stroma thylakoids, while in chromalveolates, they are nearly equally distributed [6]. Chlorophytes use LHCs specific for either PSI or PSII (Figure 2), and stramenopiles such as diatoms use fucoxanthin chlorophyll binding proteins (FCPs) in a similar capacity [7•]. Stramenopile FCPs have a carotenoid:chlorophyll ratio of 4:4 compared with 14:4 in LHCs for chlorophytes, resulting in a shift of absorbance into the 460–570 nm range, which is not accessible to chlorophytes [8]. Efficient photosynthesis requires balance between light absorbed by PSI and PSII and dissipation of energy from excess absorbed light.
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