COUNTING NATURAL POPULATIONS OF MICROCYSTIS AERUGINOSA: A SIMPLE METHOD FOR COLONY DISRUPTION INTO SINGLE CELLS AND ITS EFFECT ON CELL COUNTS OF OTHER SPECIES

SUMMARY

A rapid, high-speed blending method for disrupting colonies of the cyanobacterium Microcystis aeruginosa to single cells in preparation for cell counts is described. Cell counts obtained for treated samples of natural populations of M. aeruginosa from Hartbeespoort Dam did not differ significantly from counts obtained after colonies were disrupted by the heating method of Humphries & Widjaja (1979). Untreated, handshaken samples yielded unacceptably variable results. The effect of high-speed blending on cell counts of other common phytoplankton species was examined by comparing counts of treated vs untreated samples of natural populations. The treatment resulted In reduced cell numbers of some species, e.g. Chroomonac sp., Pediastrum boryanum, while others, e.g. Melosira granulata and Carteria sp., were not affected. Cell numbers of Pseudanabaena sp. were higher in the treated samples. This small filamentous cyanobacterium usually thrives within the mucilaginous sheath of M. aeruginosa, and is masked by the large colonies in untreated samples. We recommend this rapid and convenient sample preparation method for counting M. aeruginosa and associated organisms. Sensitive organisms should be counted on untreated aliquots of the original sample.

KEYWORDS:

• Cyanobacteria
• cell counts
• phytoplankton
• Microcystis aeruginosa
• high-speed blending