Growth and phosphate uptake kinetics of the cyanobacterium, Cylindrospermopsis raciborskii (Cyanophyceae) in throughflow cultures

1 Cylindrospermopsis raciborskii occupies a rapidly expanding geographical area. Its invasive success challenges eutrophication control in many lakes. To understand better the load-dependent behaviour of this nitrogen fixing cyanobacterium under in situ conditions, we studied P-dependent growth of a C. raciborskii strain under continuous and pulsed P supply. 2 The Droop model reasonably described P-dependent growth in the continuously supplied chemostats. Large P pulses, however, caused a delay in growth and cells subject to P pulses grew slower than their counterparts with the same P quota supplied continuously. 3 The kinetics of P uptake indicated that C. raciborskii is opportunistic with respect to P. Its high excess P storage capacity after a saturating P pulse (Qex=95 µg P [mg C]-1) and P-specific uptake capacity (Umax = Vmax/QP=150–1200) are indicative of storage adaptation. At the same time, the affinity of the P uptake system (Umax/K = 800–4000) is also high. 4 Rate of leakage exceeded that of the steady state net P uptake by one to two orders of magnitude. Growth affinity of C. raciborskii (µmax/Kµ≈ 20) was relatively low, presumably due to the substantial leakage. 5 The dynamics of the particular water body determine which trait contributes most to competitive success of C. raciborskii. In deep lakes with vertical nutrient gradients, the cyanobacterium may rely primarily on its high P storage capacity, which is coupled to a lack of short-term feedback inhibition and efficient buoyancy regulation. In lakes without such gradients, high P uptake affinity may be vitally important.