| Isochrysis zhangjiangensis is a marine microalga with potential for use in biofuel production. The alga is known to exhibit enhanced lipid and polysaccharide storage under nitrogen deficiency conditions, though the regulatory mechanism underlying this effect has not been elucidated.In this study, to monitor the metabolic transition in response to nitrogen starvation, the intracellular metabolite fluctuation within 32 hours was profiled by gas chromatography–mass spectrometry and liquid chromatography–mass spectrometry scanned in selected ion monitoring mode. The techniques identified and quantified the levels of 14 small molecular organic acids, 2 carbohydrates involved in the TCA cycle and glycolysis, and 29 free amino acids(AAs). The pulsed increase of citrate, which is the precursor of acetyl-CoA and fatty acids(FAs), indicated a potential to produce more FAs. Surprisingly, although overall AAs showed a decreasing trend under the experimental conditions, Ala and Phe showed increased levels initially. It has been postulated that a carbon flux switch between lipids and polysaccharides exists in I. zhangjiangensis. To be feasible for biofuel production, enhancement of carbon flux to lipids is expected. To facilitate the intracellular lipid deposition, together with nitrogen deficiency, a β-1,3-glucanase inhibitor(Micafungin) was introduced to block the formation of the major polysaccharide in I. zhangjiangensis, chrysolaminarin. As expected, the treatment resulted in the reduction of polysaccharides and increase of total lipids. Additionally, some AAs and other metabolites involved in the TCA cycle and glycolysis, were also perturbed by the treatment with micafungin. Most significantly, GABA was profoundly affected although the effects of micafungin were only transient. This study indicates that β-1,3-glucanase could be a good candidate for further genetic manipulation and that the possibility of regulating GABA for high oil yield warrants detailed study. |
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