Factors affecting akinete differentiation in Cylindrospermopsis raciborskii (Nostocals, Cyanobacteria)

1. Cylindrospermopsis raciborskii is a potentially toxic freshwater cyanobacterium which can produce akinetes (reproductive spores) that on germinating can contribute to future populations. To further understand factors controlling the formation of these specialised cells, the effects of diurnal temperature fluctuations (magnitude and frequency), in combination with different light intensities and phosphorus concentrations were investigated under laboratory conditions. 2. Akinete differentiation was affected by the frequency of temperature fluctuations. Maximum akinete concentrations were observed in cultures that experienced multiple diurnal temperature fluctuations. 3. Akinete concentrations increased with increasing magnitude of temperature fluctuation. A maximum akinete concentration was achieved under multiple diurnal temperature fluctuations with a magnitude of 10degreesC (25degreesC to 15degreesC). 4. A fourfold increase in light intensity (25-100 mumol m(-2) s(-1)) resulted in an approximate 14-fold increase in akinete concentration. 5. High filterable reactive phosphorus (FRP) concentrations (> 70 mug L-1) in the medium, combined with a multiple diurnal temperature fluctuation of 10degreesC, supported the development of the highest akinete concentration.