Optimization of a standard method for enumeration of total cell counts of colonial Microcystis aeruginosa in environmental samples collected from Boralasgamuwa Lake

Abstract

Effectiveness of alkaline hydrolysis, heating and regression method for enumeration of cells of Microcystis aeruginosa was assessed using water samples collected from Boralasgamuwa lake during the bloom period from 15th February to 15th May 2013. Alkaline hydrolysis was performed using; 0.01, 0.1 and 1.0 M of NaOH with a control. Alkaline hydrolysis at 800C with NaOH for 15 minutes followed by 30s vortexing produced single cells of all the test samples. A total of 2.34 ± 0.11 x105 cells/ml of single cells were generated during hydrolysis with 0.01 M NaOH. The use of higher NaOH molarities resulted in cell losses. The control sample which contained only distilled water resulted highest numbers of single cells (2.89 ±0.01 X 105 cells/ml). The heating method was employed by heating M. aeroginosa colonies at 40 0C, 60 0C,70 0C,80 0C and 90 0C for 15 minutes. Heating at 800C for 15 min, followed by 30s vortex-mixing produced a suspension of single cells with 2.76±0.81x105 cells/ml. A standard plot was developed for the direct enumeration of cell number against the area of M.aeroginosa colonies using 30 selected colonies. The standard plot slightly overestimated the cell counts during enumeration (2.98 0±.51x105 cells/ml).

Key words: Enumeration of cell counts, Microcystis aeruginosa, Alkaline hydrolysis, Heating method