Initial growth phases of two bloom-forming cyanobacteria (Cylindrospermopsis raciborskii and Planktothrix agardhii) in monocultures and mixed cultures depending on light and nutrient conditions

¹ Laboratoire de Pathologies des Animaux Aquatiques, Institut National des Sciences et Technologies de la Mer, 2025 Salammbô, Tunisia
² UMR 7245 CNRS-MNHN Molécules de communication et adaptation des micro-organismes, Muséum national d'Histoire naturelle, Case 39, 12, rue Buffon, F-75231 Paris cedex 05, France
³ Faculty of Biology, VNU University of Science, Vietnam National University, Hanoi, Vietnam

^* Corresponding author: kcomte@mnhn.fr

Received: 20 November 2013
Accepted: 14 May 2014

Abstract

Proliferations of cyanobacteria have detrimental effects on ecosystem functioning, and on the global freshwater food chain. Many studies have focused on the “in situ” dynamics of bloom-forming cyanobacteria, including Cylindrospermopsis raciborskii and Planktothrix agardhii. Few have used experimental assays to explore the fast-growing ability of naturally co-occurring species. Here we investigated the growth of these species when exposed separately (i.e., in monocultures) to a range of light and nutrient conditions, plus their interactive performances in mixed cultures in a short-time experiment (6 days). The use of microplates made it possible to carry out multiple measurements of in-vivo fluorescence (IVF), and to monitor species-dependent biovolumes. No allelopathic effect was significantly observed for any target species, while significantly lower growth rates were obtained in mixed cultures, which may reflect other interference interactions between the species. We showed that Planktothrix grew faster with low light intensity and high nutrient concentrations, and was drastically inhibited by nitrogen deprivation, in contrast to Cylindrospermopsis. However, Cylindrospermopsis outgrew Planktothrix at high NH₄⁺ concentrations, suggesting that this species may be a serious competitor for the native species in many water systems.