Impact of irradiance on the C allocation in the coastal marine diatom Skeletonema marinoi Sarno and Zingone*

Abstract

ABSTRACT. Inorganic carbon acquisition, fixation and allocation, and silicic acid and orthophosphate uptake were also studied. The C : P ratio was below the Redfield ratio, especially at LL. In HL cells, N quota was halved, C quota was similar, silica quota was lower, growth rate and long-term net primary productivity were almost doubled, relative to LL cells. The HL : LL cell quota ratios were 6 for lipid, 0.5 for protein and 0.4 for carbohydrate. Phosphoenolpyruvate carboxylase (PEPc) and glutamine synthetase (GS) activities were unaffected by the growth irradiance; phosphoenolpyruvate carboxykinase (PEPck) was 2.5-fold more active in LL cells. This suggests that in S. marinoi, C4 photosynthesis is unlikely, PEPc is anaplerotic and PEPck may be involved in the conversion of lipid C to carbohydrates, especially in LL cells. Because about 50% of the cost for the production of an HL cell is caused by lipid biosynthesis, we propose that the preferential allocation of C to lipid at HL takes advantage of the relatively high volumebased energy content of lipids, in an organism that reduces its size at each vegetative cell division.

Elevated CO 2 and Phosphate Limitation Favor Micromonas pusilla through Stimulated Growth and Reduced Viral Impact

“…Thus, these cells had relatively high NPP compared to the growth rate. Carbon fixation has been proposed to be a way to deal with excess energy (57). The drastic decrease in Fv/Fm, epoxidation state, and Chl a/Chl b ratio for the 0.32-max culture compared to the 0.97-max and the P-replete cultures is in agreement with the necessity to dissipate excess energy for the cells under this treatment.…”

Effect of light intensity on physiological changes, carbon allocation and neutral lipid accumulation in oleaginous microalgae

“…There is evidence that the shift of carbon fluxes from carbohydrate to lipid biosynthesis in microalgae species is possible. The energy demand for the biosynthesis of lipids was much higher than that of carbohydrates (lipid has a much higher energy value, about 2.25 times), therefore lipids could serve as an effective energy and carbon storage providing a larger sink for the available energy, especially when light was in excess to the requirement for growth (Li et al, 2011;Norici et al, 2011;Msanne et al, 2012). Furthermore, the enhanced synthesis of lipid (TAG) can consumed excessive electrons from over-reduced photosynthetic electron transport chain under high light stress.…”

“…However, those stress generally concomitant with lower biomass productivity and thus low overall lipid productivity (Hu et al, 2008;Ho et al, 2014). Light supply as an environmental factors not only greatly affect algae photosynthesis as well as cell composition and metabolic pathway, but also the economic efficiency of the algae cultivation process (Norici et al, 2011;He et al, 2015), and consequently, the supply and efficient utilization of light energy have been the greatest scientific and technological challenge in http://dx.doi.org/10.1016/j.biortech.2015.05.021 0960-8524/Ó 2015 Elsevier Ltd. All rights reserved. research and development on commercial cultivation of microalgae.…”

Gene Regulation of Carbon Fixation, Storage, and Utilization in the DiatomPhaeodactylum tricornutumAcclimated to Light/Dark Cycles

“…Fatty acids store more energy in smaller molecules, but the processes of lipid synthesis and catabolism are slower compared with carbohydrate metabolism (Lancelot and Mathot, 1985). It has been shown that other factors such as nutrient depletion (Reitan et al, 1994;Breteler et al, 2005) or excess light energy (Norici et al, 2011) may increase cellular lipid content in diatoms. Along with the mapping and identification of protein coding regions of microalgae genomes, genetic engineering is a rapidly developing field that may provide a tool to enhance lipid synthesis and storage in algae for use in biofuel production (Radakovits et al, 2010).…”