Effects of starch synthesis defection on the acyl profiling of glycerides in Chlamydomonas reinhardtii

Abstract:

[Objective] With the defection in starch synthesis in mutated Chlamydomonas reinhardtii CC-4326, the effects on the acyl profiling variation of glycerides were inspected with or without nitrogen deficiency stress. It provided basic information to understand glyceride metabolism. Wild type strain CC-137 was chosen as the control. [Methods] Cultivations were carried out in both shake flasks and 500 mL cylindrical bubbling photobioreactors under nitrogen rich or deficient conditions. Triacylglycerols were purified by thin-layer chromatography. After transesterified with methanol, acyls were quantified by gas chromatography with an internal standard and the abundance of acyls in glycerides and triacylglycerols were compared. [Results] The amount of C16:4 and C18:3 in each strain accounted for about 45% of total acyls under nitrogen rich condition in both shake flask and photobioreactor cultivation. With nitrogen supply, CC-4326 showed no difference in the abundance and changing pattern of the above two major acyls in glycerides, whereas the wild type showed higher increase and higher abundance of these two acyls in shake flasks than in photobioreactors. However, without nitrogen supply, the difference in the accumulation of triacylglycerols was observed between strains. In photobioreactors, CC-4326 accumulated 0.5 fold more triacylglycerols than CC-137, whereas in shake flasks, the difference was not significant. As an indicator, C18:1 was increased significantly in glycerides and triacylglycerols of both strains. And the same as triacylglycerol accumulation, C18:1 increased faster in photobioreactors than in shake flasks. As contrast, CC-137 showed similar triacylglycerol level in the matter of weight percentage of biomass, however, with higher monounsaturated fatty acids in shake flasks than in photobioreactors. It suggested that triacylglycerols can be more effectively induced in the shake flasks than in photobioreactors. But the highest triacylglycerol accumulation achieved in CC-4326 with 12.8% in dry weight, which were cultured in the photobioreactors under nitrogen depletion. [Conclusion] By inhibiting the starch synthesis, comparing to CC-137, CC-4326 obtains the high efficient triacylglycerol accumulation in photobioreactors with nitrogen depletion regulation.