Abstract
Chlorella sorokiniana is an important industry microalga potential for biofuel production. Inoculum size is one of the important factors in algal large-scale culture, and has great effects on the growth, lipid accumulation and metabolism of microalgae. As the first barrier of cell contents, membrane plays a vital role in algal inoculum-related metabolism. The knowledge of phospholipids, the main membrane component and high accumulation of phospholipids as the major content of total lipids mass in some microalgae, is necessary to understand the role of membrane in cell growth and metabolism under different inoculum density. Profiling of C. sorokiniana phospholipids with LC-MS led to the identification of 119 phospholipid species. To discover the phospholipid molecules most related to change of inoculum sizes, Partial Least Squares Discriminant Analysis (PLS-DA) was employed and the results revealed that inoculum sizes significantly affected phospholipid profiling. Phosphatidylglycerol (PG), phosphatidyl- ethanolamine (PE) and several phosphatidylcholine (PC) species might play an important role under our experimental conditions. Further analysis of these biomarkers indicated that cell membrane status of C. sorokiniana might play an important role in the adaption to the inoculum sizes. And the culture with inoculum size of 1×106 cells mL−1 presented the best membrane status with the highest content of PC and PG, and the lowest content of PE. We discovered that the inoculum size of 1×106 cells mL−1 might provide the best growth condition for C. sorokiniana. Also we proposed that PG, PE and several PC may play an important role in inoculum-related metabolism in C. sorokiniana, which may work through thylakoid membrane and photosynthetic pathway. Thus this study would provide more potential targets for metabolic engineering to improve biofuel production and productivity in microalgae.
Highlights
The demand of energy has risen rapidly because of the modernization and the industrialization of the world
All phospholipid samples extracted from C. sorokiniana were analyzed under the optimal LC-MS conditions
Pineau constructed two mutants of Chlamydomonas reinhardtii characterized by a remarkable reduction in their PG contents together with a complete loss in its D3-trans hexadecenoic acid-containing form, lost PSII activity [74]. All these results indicated that PG was the essential component for formation of the thylakoid membranes, and might be an important part involved in photosynthesis
Summary
The demand of energy has risen rapidly because of the modernization and the industrialization of the world. Amongst the renewable energies,, biofuels derived from microorganism is one of the most promising alternative to fossil fuel-based energy sources [2,3]. Researchers studied microalgae cultivation and microalgal biofuel production from different directions, such as expanding the new application of algae, system screening of valuable algae strains [4], optimization of process conditions [5,6], investigation of metabolic pathways [7,8], metabolic engineering [9,10], genome analysis [11] and so on. The algae oils are mainly composed of triacylglycerols (TAG), diacylglycerols (DAG), free fatty acids (FFA) and phospholipids (PL), and TAG contributes more than 80% of algae lipid mass. Previous studies have shown that phospholipid synthesis precursors, DAG and FFA, could be derived from TAG, and from membrane phospholipids [21]
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