Date Published: March 27, 2017
Publisher: Public Library of Science
Author(s): Likun Wei, Xuxiong Huang, Gotthard Kunze.
Microalga Nannochloropsis oculata is a promising alternative feedstock for biodiesel. Elevating its oil-yielding capacity is conducive to cost-saving biodiesel production. However, the regulatory processes of multi-factor collaborative stresses (MFCS) on the oil-yielding performance of N. oculata are unclear. The duration effects of MFCS (high irradiation, nitrogen deficiency and elevated iron supplementation) on N. oculata were investigated in an 18-d batch culture. Despite the reduction in cell division, the biomass concentration increased, resulting from the large accumulation of the carbon/energy-reservoir. However, different storage forms were found in different cellular storage compounds, and both the protein content and pigment composition swiftly and drastically changed. The analysis of four biodiesel properties using pertinent empirical equations indicated their progressive effective improvement in lipid classes and fatty acid composition. The variation curve of neutral lipid productivity was monitored with fluorescent Nile red and was closely correlated to the results from conventional methods. In addition, a series of changes in the organelles (e.g., chloroplast, lipid body and vacuole) and cell shape, dependent on the stress duration, were observed by TEM and LSCM. These changes presumably played an important role in the acclimation of N. oculata to MFCS and accordingly improved its oil-yielding performance.
Microalgae are a diverse group of microorganisms with various unique biological characteristics, including high photosynthetic energy transfer efficiency, high biomass productivity, excellent adaptability to various environments and capability of producing a broad variety of bioenergy [1–3]. For example, the members of Nannochloropsis genus are marine Eustigmatophyceae microalgae with advantages such as fast growth and easy cultivation, capable of storing large triacylglycerols (TAGs) under particular culture conditions and are therefore an environmentally friendly biodiesel feedstock with great developmental potential . However, microalgae biodiesel still faces many problems in commercial production, such as high oil-yielding species to be screened or constructed, and technological innovations in large-scale cultivation, harvesting, oil extraction and transesterification of biolipids to biodiesel .