PRACTICAL 8: ESTIMATION OF MICROALGAL CELL DENSITIES

INTRODUCTION

Microalgae cell counting is one way to estimate the density of microalgae in a volume. Cell number of microalgae can be determined using a haemacytometer. The haemacytometer is suitable for cells in the range of blood cells (i.e. less than about 100 µm in diameter) and for cell densities less than 10⁵/mL. Larger cells than 100 µm are better counted using the Sedgwick-Rafter chamber (N.R. Moheimani, et all., 2013).

OBJECTIVE

To counting the density of microalgae culture.

METHODOLOGY

A. Estimation of Microalgae Cell Densities

1. a growing culture of Chlorella sp. and Nannochloropsis sp. will be provided.

2. a glass slide is placed on the top of the haemacytometer.

3. 10 µl of the microalgae culture is taken carefully using pipette.

4. the algal cells are counted under 400x (40x ocular) magnification.

5. algal cells suspension should be diluted enough, so that it can be counted between 100-300 algal cells per quadrant (<50 cells in one box).

6. the counts in the quadrants are taken the average and the algal density in the sample is calculated, taking into account the dilution factor

7. for cells that overlap the quadrant borders, the cells on the top and right borders are counted, and omit the cells on the bottom and left borders of the quadrants. (each quadrant has an area of 1 mm², is 0,1 mm deep and has a volume of 1 x 10^-4 mL).

B. Calculation

1. the cells are counted in the 4 corner quadrants of the counting chamber.

2. the cell density (cell/mL) is calculated using the formula bellow :

            i) (average no of cells below and above) x 10000 x df

            ii) (total cell count) x 2500 x df 

RESULTS

Times of Counting	Microalgae Density (cell/mL)
	Chlorella sp.	Nannochloropsis sp.
1	1,55 x106	2,20 x 106
2	0,80 x 106	3,05 x 106
3	0,75 x 106	2,75 x 106
Average	1,03 x 106	2,67 x 106

Table 1: Microalgae densities for 3 times counting

DISCUSSION

Counting cells of microalgae in this practical were done triplet of counting to get more accurate number of cells and reduce human error. Sample of Chlorella sp. was diluted for two times because it has high stocking density. By having the density of microalgae that cultured, it can be used to calculate how many sample volume of microalgae will be transferred into a new medium or even given to the fish, and also to determine the cells growth of microalgae.

Direct cell counting using haemacytometer has the advantage over other methods (e.g. optical density or using a particle counter) in that one is also closely observing the cells and any anomalies such as changes in cell morphology and/or the presence of contaminans will be detected easily; however it is also time-consuming (N.R. Moheimani, et all., 2013).

CONCLUSION

Microalgae density is one of important parameter in culturing microalgae. It can get by counting the cells of microalgae.

REFERENCES

N.R. Moheimani, M.A. Borowitzka, A. Isdepsky, S.F. Sing, 2013, Algae for Biofuels and Energy; Standard methods for measuring growth of algae and their composition, Developments in Applied Phycology 5, Springer Science and Business Media Dordrecht.