An ideal screen would consider growth physiology, including cell size and numbers, and metabolite production of algal strains. The algal growth physiology for biofuel encompasses a number of parameters, such as maximum cell density, maximum spe­cific growth rate, and tolerance to environmental variables such as temperature, pH, salinity, oxygen levels, CO2 levels, and nutrient requirements (Chisti, 2007; Brennan and Owende, 2010). Because all these parameters require significant experimental effort, the development of automated systems that provide information regarding all parameters simultaneously would be helpful. Screening for metabolite production may involve determining the cellular composition of proteins, lipids, and carbohy­drates, and measuring the productivity of the organism regarding metabolites useful for biofuel generation. The exact screenings employed would depend on the cultiva­tion approaches and fuel precursor desired. For example, a helpful screening for oil production would allow for distinguishing between neutral and polar lipids, and would provide fatty acid profiles. Furthermore, many strains also secrete metabolites

Advantages and Disadvantages of Microalgal Purification Techniques

into the growth medium. Some of these could prove valuable as co-products, and new approaches are needed to develop screening methods for extracellular mate­rials. For mass culture of a given algal strain, it is also important to consider the strain’s robustness, which includes parameters such as culture consistency, resil­ience, community stability, and susceptibility to predators present in a given envi­ronment. Previous studies revealed that algal strains tested in the laboratory do not always perform similarly in outdoor mass cultures (Sheehan et al., 1998). Therefore, to determine a strain’s robustness, small-scale simulations of mass culture conditions must be performed.

At this time, the bottleneck in screening large numbers of algae stems from a lack of high-throughput methodologies that would allow simultaneous screening of multiple phenotypes, such as growth rate and metabolite productivity. Solvent extraction, for example, is the most common method for the determination of lipid content in algae, but it requires a significant quantity of biomass (Bligh and Dyer, 1959; Ahlgren and Merino, 1991). Fluorescent methods using lipid-soluble dyes have also been described, and although these methods require much less biomass (as little as a single cell), it has not yet been established if these methods are valid across a wide range of algal strains (De la Jara et al., 2003; Elsey et al., 2007). Further improvements in analytical methodology could be made through the development of solid-state screening methods. Not only are rapid screening procedures necessary for the biofuels field, but they also could prove extremely useful for the identifica­tion of species, particularly in mixed field samples necessary for the future of algal ecology. They could also reduce the number of redundant screens of algal species.