Potential triggers for akinete differentiation in an Australian strain of the cyanobacterium Cylindrospermopsis raciborskii (AWT 205/1)

Abstract

Understanding the triggers for some cyanobacteria of the Nostocales and Stigonematales orders to produce specialised reproductive cells termed akinetes, is very important to gain further insights into their ecology. By improving our understanding of their life cycle, appropriate management options may be devised to control the formation of these cells, and therefore the potential bloom inoculum which they are thought to provide, may be reduced. This study investigated the effect of chemical (phosphorus limitation), and environmental variables (temperature shock) on akinete differentiation in the freshwater cyanobacterium Cylindrospermopsis raciborskii (AWT 205/1). From the preliminary results, it is suggested that the availability of phosphorus and changes in temperature were a necessary requirement for the formation of akinetes in this particular strain of C. raciborskii. In the four phosphorus treatments investigated (0, 3, 38 and 75 μg l⁻¹ P), only the two higher treatments produced akinetes (approximately 220 ml⁻¹). When the first akinetes were observed in the 38 and 75 μg l⁻¹ P treatments, filterable reactive phosphorus (FRP) concentrations in the medium were approximately 22 and 52 μg l⁻¹ P, respectively, indicating that there was no phosphorus limitation. In the temperature shock experiment, akinetes were observed in the 15 and 20 °C treatments. However, akinetes were degraded (pale yellow colour, limited swelling and shrivelled edges) and in much lower concentrations, which was thought to be a result of the daily temperature shock. We suggest that the formation of akinetes in C. raciborskii (AWT 205/1) can be triggered by an initial temperature shock and that phosphorus is a necessary requirement to allow further growth and full development of akinetes.