ABSTRACT
Microalgae have been considered for biodiesel production, based on their ability to grow rapidly and to accumulate large amounts of storage lipids, primarily in the form of triacylglycerides (TAG). Microalgae are a group of mostly photoautotrophic microorganisms that includes both prokaryotic and eukaryotic species. These organisms can photosynthetically convert CO2 and minerals to biomass, but some species also grow heterotrophically. Prokaryotic microalgae are cyanobacteria (blue-green algae) and eukaryotic microalgae include the nine phyla Glaucophyta, Chlorophyta, Chlorarachniophyta, Euglenophyta, Rhodophyta, Cryptophyta, Heterokontophyta, Haptophyta and Dinophyta. To date, about 2/3 of 50,000 species have been identified and are kept in collection by various algal research institutes [1]. For example, the largest collection at present is the Collection of Freshwater Algae at the University of Coimbra, Portugal, maintaining about 4000 strains and 1000 species of algae; the Culture Collection of Algae of the Göttingen University, Germany harbors 2213 strains and 1273 species of both freshwater and marine algae; the
Culture Collection of Algae in the University of Texas, USA, maintains 2300 strains of freshwater species; the National Institute for Environmental Studies in Japan is keeping 2150 strains with about 700 species of freshwater and marine algae [2]; the Australian National Algae Culture Collection (ANACC) maintains about 1000 strains of microalgae which were mostly isolated from Australian waters [3]. Although algae collections are maintained for many purposes (e.g., for pharmaceutical, food, energy and industrial products), only a few hundred strains have been investigated for chemical content and very few are cultivated in industrial quantities. To date, although there is mounting interest to develop microalgal biodiesel production, the cost for microalgal biomass production is currently much higher than from other energy crops [4]. Thus, selection of an energy and cost-efficient production model could play a very important role in achieving competitive biodiesel production. This includes the selection of high lipid-producing algae, suitable farming locations, efficient cultivation and harvesting methods and oil extraction procedures. Here, we focus on the first step, the selection of suitable high lipid-accumulating microalgae strains, a process that can be compared with the early domestication of current crop plants. In alignment with this purpose, this review aims to present a practical guide to several simple and robust methods for microalgae isolation and selection for traits that maybe most relevant for commercial biodiesel production.
