Microbial lipid production from renewable and waste materials for second-generation biodiesel feedstock

Microbes have been exploited to produce a variety of high-value products such as enzymes, proteins, antibiotics, vitamins, etc. Use of oleaginous microorganisms for production of lipids (commonly called as single cell oils) commenced during the eighteenth century in Germany. Microbial lipids containing special fatty acids such as gamma-linolenic acid, arachidonic acid and docosahexaenoic acid are popularized and are now being produced in a large scale as neutraceuticals and food additives. In the past decade, microbial lipids have been considered as a promising feedstock for biodiesel production due to the contemporary issues on climate change, renewable energy and food security. Recently, various cheap raw materials and biowastes have been explored for economic microbial lipid production, which is considered as a solution to reduce biodiesel production cost and to achieve sustainable management of biowastes. Thus, microbial lipids produced from renewable biomass and biowastes as a second-generation biodiesel feedstock are a promising alternative for vegetable oils. In this review historical development of microbial lipids, biochemistry of lipid accumulation by oleaginous microorganisms, lipid production from various biowastes and renewable materials and cultivation methodologies are reviewed. Microbial lipids as a biodiesel feedstock are also reviewed and discussed.