Abstract
Microalgae are receiving increasing attention as alternative production systems for renewable energy such as biofuel. The photosynthetic alga Chlamydomonas reinhardtii is widely recognized as the model system to study all aspects of algal physiology, including the molecular mechanisms underlying the accumulation of starch and triacylglycerol (TAG), which are the precursors of biofuel. All of these pathways not only require a carbon (C) supply but also are strongly dependent on a source of nitrogen (N) to sustain optimal growth rate and biomass production. In order to gain a better understanding of the regulation of C and N metabolisms and the accumulation of storage carbohydrates, the effect of different N sources (NH4NO3 and ) on primary metabolism using various mutants impaired in either NIA1, NIT2 or both loci was performed by metabolic analyses. The data demonstrated that, using NH4NO3, nia1 strain displayed the most striking phenotype, including an inhibition of growth, accumulation of intracellular nitrate, and strong starch and TAG accumulation. The measurements of the different C and N intermediate levels (amino, organic, and fatty acids), together with the determination of acetate and remaining in the medium, clearly excluded the hypothesis of a slower and acetate assimilation in this mutant in the presence of NH4NO3. The results provide evidence of the implication of intracellular nitrate and NIT2 in the control of C partitioning into different storage carbohydrates under mixotrophic conditions in Chlamydomonas. The underlying mechanisms and implications for strategies to increase biomass yield and storage product composition in oleaginous algae are discussed.
Highlights
For photosynthetic organisms, such as higher plants and green microalgae, inorganic nitrogen (N) is one of the essential nutrients and the most limiting mineral element for growth and yield (Kropat et al, 2011)
The results provide evidence of the implication of intracellular nitrate and NIT2 in the control of C partitioning into different storage carbohydrates under mixotrophic conditions in Chlamydomonas
In Chlamydomonas, biochemical and genetic analyses have allowed the identification and characterization of most of the different components involved in NO3– transport and assimilation, with some participating in NO3– signalling pathways, including the structural gene NIA1 encoding nitrate reductase (NR) (EC. 1.6.6.2) and the NIT2 regulator, which is considered a central regulatory gene required for NO3– signalling
Summary
For photosynthetic organisms, such as higher plants and green microalgae, inorganic nitrogen (N) is one of the essential nutrients and the most limiting mineral element for growth and yield (Kropat et al, 2011). Ammonium (NH+4 ) and nitrate (NO3–) are the major primary sources of N in higher plants and microorganisms, and their respective use is strongly dependent on the species and the environmental conditions. Nitrite reductases, NR and NiR, respectively), leading to NH+4 , which is directly incorporated into central. In Chlamydomonas, nitrate reduction is catalysed by a homodimeric NAD(P)H–NR complex containing two activities: NAD(P)H-cytochrome c reductase (diaphorase, EC 1.6.6.1-3) and reduced benzyl viologen NRs (terminal NR) (Kalakoutskii and Fernández, 1995)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
