Metabolic and morphological changes of an oil accumulating trebouxiophycean alga in nitrogen-deficient conditions

Takuro Ito,Takashi Nakada,Tomoyoshi Soga,Norihide Kurano,Yoshitaka Ano,Masaru Tomita,Miho Tanaka,Haruka Shinkawa

doi:10.1007/s11306-012-0463-z

Abstract

Oil-rich algae have promising potential for a next-generation biofuel feedstock. Pseudochoricystis ellipsoidea MBIC 11204, a novel unicellular green algal strain, accumulates a large amount of oil (lipids) in nitrogen-deficient (–N) conditions. Although the oil bodies are easily visualized by lipophilic staining in the cells, little is known about how oil bodies are metabolically synthesized. Clarifying the metabolic profiles in –N conditions is important to understand the physiological mechanisms of lipid accumulations and will be useful to optimize culture conditions efficiently produce industrial oil. Metabolome and lipidome profiles were obtained, respectively, using capillary electrophoresis- and liquid chromatography-mass spectrometry from P. ellipsoidea in both nitrogen-rich (+N; rapid growth) and –N conditions. Relative quantities of more than 300 metabolites were systematically compared between these two conditions. Amino acids in nitrogen assimilation and N-transporting metabolisms were decreased to 1/20 the amount, or less, in –N conditions. In lipid metabolism, the quantities of neutral lipids increased greatly in –N conditions; however, quantities of nearly all the other lipids either decreased or only changed slightly. The morphological changes in +N and –N conditions were also provided by microscopy, and we discuss their relationship to the metabolic changes. This is the first approach to understand the novel algal strain’s metabolism using a combination of wide-scale metabolome analysis and morphological analysis.Electronic supplementary materialThe online version of this article (doi:10.1007/s11306-012-0463-z) contains supplementary material, which is available to authorized users.

Highlights

Oil-rich algae are expected to be a promising source of nextgeneration bioenergy because microalgae have the potential to produce up to 300 times more lipids than major oil crops based on biofuel feedstock production per area (Schenk et al 2008)
In ?N conditions, the culture included a peak corresponding to sporangia (Fig. 1m), while we found only a single vegetative peak in –N conditions
In –N conditions, P. ellipsoidea reduced in cell size, because A5–N does not include nitrogen source for de novo synthesis of amino acids, and the cell divisions continued in this oligotrophic environment

Summary

Introduction

Oil-rich algae are expected to be a promising source of nextgeneration bioenergy because microalgae have the potential to produce up to 300 times more lipids than major oil crops based on biofuel feedstock production per area (Schenk et al 2008). S179 mainly marine algae, contain oil bodies in normal culture conditions (Shifrin and Chisholm 1981, Sheehan et al 1998, Hu et al 2008). Accumulating oil, known as lipid accumulate conditions, principally triacylglycerols (TAGs), in response to –N conditions, has been observed in numerous species or strains of various algal taxa, and in several different culture conditions, which are other nutrient-deficient, and in chemical stimulus and physical stress (Basova 2005, Liu et al 2008, Merzlyak et al 2007, Roessler 1990, Shifrin and Chisholm 1981, Thompson 1996). Based on the sequence homology and some shared biochemical characteristics, researchers believe that green algae share basic lipid-synthetic pathways with higher plants; lipid synthesis and accumulation mechanisms in stress conditions are barely characterized in algae (Hu et al 2008, Thompson 1996)

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