Enumeration of Microalgal Cells - Biotechnological Applications of Microalgae - page 48

with isotonic ammonium formate (NH 4 HCO 2 , 2%) to remove suspended residual
salts (Valenzuela-Espinoza et al., 2002). The advantage of using ammonium formate
is that it does not leave any residue as it decomposes to volatile compounds during
the drying process. An empty watch glass is weighed and the microalgal sample
pellet transferred to the watch glass. The biomass is dried in an oven at 60°C for
12 hours. After drying, the weight of the watch glass plus the dry biomass is deter-
mined, and the net dry cell weight (DCW) is calculated using Equation (4.1):
DCW (mg L −1 ) = [{Watch glass (mg) + Dry biomass (mg)}
− Watch glass (mg)]/Volume (L) (4.1)
4.4.3 C ountinG C haMbers
The counting chamber methods are well established and frequently applied for micro-
algal enumeration due to their low cost and easy application. The three common types
of counting chamber methods for microalgae enumeration are the (1) Sedgewick-
Rafter counting slide, (2) Palmer-Maloney counting slide, and (3) haemocytometer
counting slide (LeGresley and McDermott, 2010). The three methods require sam-
ples with high cell densities. The presence of contaminating particles in the same size
range as the algae and failure of cells to separate after cell division may be possible
sources of erroneous counts (Coutteau, 1996). Table 4.1 compares the merits and
drawbacks as well as fundamentals of the three counting chamber methods.
4.4.4 F flow C ytoMetry
Flow cytometry (FCM) is an automated cell counting technique that captures the
fluorescence and scatter properties of the microalgal cells. The major advantage
of automated cell counting techniques over optical microscopy is that they mini-
mize the errors associated with human counting (Marie et al., 2005). The use of this
highly sophisticated technique is hindered by the cost of the equipment as well as
the requirement of highly skilled and trained personnel to operate the instrument.
In addition, this technique is also plagued by limited sensitivity at lower microalgal
cell concentrations. The solid-phase cytometer method for conducting total direct
counts of bacteria is less biased and has performed significantly better than any of
the microscopic methods (Lisle et al., 2004). Basic image analysis methods do not
generally discriminate between phytoplankton and other material such as detritus
and sediment in samples, thereby presenting a problem in the application to routine
field samples. This technique may be more useful for the analysis of cultures and
mono-specific high-density blooms (Karlson et al., 2010).
4.5 CONCLUSION
Microalgal enumeration can be tedious and cumbersome due to the small size of
microalgal cells. Furthermore, this is exacerbated by the prohibitive cost of the
available sophisticated equipment. To date, however, microalgal enumeration has
been accomplished by gravimetric analysis, counting chambers, and flow cytometry.