Strain Selection for Biodiesel Production - Biotechnological Applications of Microalgae - page 28

taxonomic consideration (Tang and Dobbs, 2007). Hence, flow cytometry, coupled
with cell sorting, can signify a vital tool for screening and exploiting microalgal
strains for specific drives, including biodiesel feedstock development. As compared
to fluorescence microscopy, flow cytometry helps the investigator perform rapid and
quantitative experimentation. Fluorescence-activated cell sorting (FACS) permits
cells with a specific characteristic—or indeed a combination of characteristics—to
be separated from the sample. Sinigalliano et al. (2009) compared electronic cell
sorting and conventional methods of micropipette cell isolation with dinoflagellates
and other marine eukaryotic phytoplankton. Fragile dinoflagellates such as Karenia
brevis (Dinophyceae) were distressed upon conventional micropipette procedures
while cells were viable on electronic sorting. However, electronic single-cell sorting
combined with automated techniques for growth screening has the possibility of
screening novel algal strains (Sinigalliano et al., 2009). The benefits and shortcom-
ings of the microalgal isolation and purification protocols described in this section
are summarized in Table 3.5.
In addition, several immunological and nonimmunological methods to isolate
desired unicellular algal cells exist. The immunologic reaction of a specific inte-
grated protein on the membrane decides the protocol for cell separation. Large-scale
commercialized cell separation involves techniques such as FACS (Takahashi et al.,
2004), magnetic-activated cell sorting (Han and Frazier, 2005), and affinity-based
cell sorting (Chang et al., 2005), all of which are highly specific and selective.
But the limitation is that the immunologically isolated cells may undergo trauma
and the inclusive separation system involves high cost. Further, immunoreactions
and follow-up elution with capturing antibodies are quite complicated processes.
Alternatively, nonimmunological techniques such as dielectrophoresis (Doh and
Cho, 2005), hydrodynamic separation (Shevkoplyas et al., 2005), aqueous two-phase
system (Yamada et al., 2002), and ultrasound separation (Petersson et al., 2004) have
also been employed. These methods work based on the interactive physico-chemical
property of a cell with that of the surrounding media, and lack specificity.
3.4 SCREENING CRITERIA AND METHODS
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 spe-
cific growth rate, and tolerance to environmental variables such as temperature, pH,
salinity, oxygen levels, CO 2 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 carbohy-
drates, and measuring the productivity of the organism regarding metabolites useful
for biofuel generation. The exact screenings employed would depend on the cultiva-
tion 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