Abstract
Microalgal lipids have been considered as a promising source for biodiesel production. Alkaline pH can induce neutral lipid accumulation in microalgae cells. However, whether and how proton pumps, especially vacuolar H+-ATPase (V-ATPase), function in these processes is not well known. In this study, we treated Phaeodactylum tricornutum with V-ATPase specific inhibitor bafilomycin A1 (BFA1) to determine its role in lipid production. Firstly, V-ATPase activity was increased in the latter phase of microalgae growth. BFA1 treatment decreased the cell density and lipid contents. Further analysis showed that BFA1 treatment reduced the number and size of oil bodies. GC-MS analysis showed that lipid components were not affected by BFA1 treatment. Intracellular pH was decreased and nitrogen depletion was delayed after BFA1 treatment. RNA-Seq analysis showed that expression of genes involved in calcium signaling, sulfur metabolism, cell cycle, glycolysis, pentose phosphate pathway, porphyrin, chlorophyll metabolism and lipid catabolic metabolism were upregulated, while expression of genes involved in ion transmembrane transport, ubiquitin mediated proteolysis, SNARE interactions in vesicular transport, fatty acid biosynthesis were downregulated under BFA1 treatment. Our findings provided insights into the molecular mechanisms underlying lipid accumulation and the key genes involved in lipid metabolism in Phaeodactylum tricornutum in response to BFA1.
Highlights
Biodiesel is a new type of green bioenergy, which has attracted considerable attention as a potential alternative to fossil fuels[1]
By using RNA-seq approach, we demonstrated that V-ATPase plays an important role in the regulation of lipid production, which is associated with energy metabolism, ion transport and cell cycle control
These results suggest that treatment with Bafilomycin A1 (BFA1) can reduce the accumulation of neutral lipids in P. tricornutum
Summary
Biodiesel is a new type of green bioenergy, which has attracted considerable attention as a potential alternative to fossil fuels[1]. P. tricornutum has attracted increasing attention as a raw material for biofuel production because it rapidly grows to high cell densities, has a short biomass doubling time, and accumulates triacylglycerols (TAGs) in the late exponential phase; storage lipids constitute at least 20–30% of the dry cell weight of this diatom under standard culture conditions[5]. Most algaes can produce both starch and lipids as energy reserves, with ratios that differ depending on growth conditions. Many algaes alter their lipid biosynthetic pathways to induce the formation and accumulation of neutral lipids, mainly in the form of TAGs8. Guckert and Cooksy demonstrated that cellular TAG accumulation can be induced in a single species of Chlorella by growing it at a pH higher than normal[14] This process was explored further and was proven applicable to other microalgal genera, such as Scenedesmus, Coelastrella and P. tricornutum[15,16]. Information on the role of these proton pumps, especially V-ATPase in lipid regulation is lacking
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