Triacylglyceride Production and Autophagous Responses in Chlamydomonas reinhardtii Depend on Resource Allocation and Carbon Source
Triacylglyceride Production and Autophagous Responses in Chlamydomonas reinhardtii Depend on Resource Allocation and Carbon Source
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DOI：
10.1128/ec.00178-13
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发表时间：
2014-03-01
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影响因子：
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通讯作者：
Smith, Alison G.
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作者：
Davey, Matthew P.;Horst, Irmtraud;Smith, Alison G.
为了提高微藻生物柴油的经济可行性，必须优化微藻细胞内三酰甘油酯(TAG)等燃料分子的生产率。为了了解代谢转换到TAG生产所需的一些触发因素，我们研究了碳供应(醋酸盐或二氧化碳)对低氮可用条件下生长的莱茵衣藻(野生型和无淀粉STA6突变体)的影响。正如预期的那样，在乙酸盐存在的情况下，Tag的初始产量比在严格的光合作用条件下要高得多，特别是对于sta6突变体来说，它不能将资源分配给淀粉。然而，在两个菌株中，混合营养培养几天后TAG产量停滞不前，而在自养条件下，TAG水平继续上升。此外，sta6突变体的生长减少意味着在自养生长的野生型中发现了最大的生产力(以mg标签升(-1)天(-1)衡量)。野生型细胞以自噬方式对低氮作出反应，表现为极性(膜)脂的降解和光合色素的丧失，这在供应醋酸盐的细胞中较少。相比之下，无论碳供应如何，在sta6突变细胞中几乎没有观察到自噬。相反，在sta6突变体中观察到了非常高水平的游离脂肪酸，这表明代谢发生了相当大的变化。这些测量表明了碳供应和菌种选择对油脂生产的重要性。我们的发现将用于工业化栽培，在自养条件下使用快速生长的野生型菌株，供应气态二氧化碳，而不是要求外源有机碳供应，将是更可取的。
To improve the economic viability of microalgal biodiesel, it will be essential to optimize the productivity of fuel molecules such as triacylglyceride (TAG) within the microalgal cell. To understand some of the triggers required for the metabolic switch to TAG production, we studied the effect of the carbon supply (acetate or CO2) in Chlamydomonas reinhardtii (wild type and the starchless sta6 mutant) grown under low N availability. As expected, initial rates of TAG production were much higher when acetate was present than under strictly photosynthetic conditions, particularly for the sta6 mutant, which cannot allocate resources to starch. However, in both strains, TAG production plateaued after a few days in mixotrophic cultures, whereas under autotrophic conditions, TAG levels continued to rise. Moreover, the reduced growth of the sta6 mutant meant that the greatest productivity (measured as mg TAG liter(-1) day(-1)) was found in the wild type growing autotrophically. Wild-type cells responded to low N by autophagy, as shown by degradation of polar (membrane) lipids and loss of photosynthetic pigments, and this was less in cells supplied with acetate. In contrast, little or no autophagy was observed in sta6 mutant cells, regardless of the carbon supply. Instead, very high levels of free fatty acids were observed in the sta6 mutant, suggesting considerable alteration in metabolism. These measurements show the importance of carbon supply and strain selection for lipid productivity. Our findings will be of use for industrial cultivation, where it will be preferable to use fast-growing wild-type strains supplied with gaseous CO2 under autotrophic conditions rather than require an exogenous supply of organic carbon.