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Applied and Environmental Microbiology, May 2007, p. 2939-2946, Vol. 73, No. 9
0099-2240/07/$08.00+0     doi:10.1128/AEM.02892-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Competition for Light between Toxic and Nontoxic Strains of the Harmful Cyanobacterium Microcystis{triangledown}

W. Edwin A. Kardinaal ,1,{dagger},{ddagger} Linda Tonk,1,{dagger} Ingmar Janse,2,§ Suzanne Hol,1 Pieter Slot,1 Jef Huisman,1 and Petra M. Visser1*

Aquatic Microbiology, Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Nieuwe Achtergracht 127, 1018 WS Amsterdam, The Netherlands,1 Department of Microbial Wetland Ecology, Centre for Limnology, Netherlands Institute of Ecology, Rijksstraatweg 6, 3631 AC Nieuwersluis, The Netherlands2

Received 14 December 2006/ Accepted 23 February 2007

The cyanobacterium Microcystis can produce microcystins, a family of toxins that are of major concern in water management. In several lakes, the average microcystin content per cell gradually declines from high levels at the onset of Microcystis blooms to low levels at the height of the bloom. Such seasonal dynamics might result from a succession of toxic to nontoxic strains. To investigate this hypothesis, we ran competition experiments with two toxic and two nontoxic Microcystis strains using light-limited chemostats. The population dynamics of these closely related strains were monitored by means of characteristic changes in light absorbance spectra and by PCR amplification of the rRNA internal transcribed spacer region in combination with denaturing gradient gel electrophoresis, which allowed identification and semiquantification of the competing strains. In all experiments, the toxic strains lost competition for light from nontoxic strains. As a consequence, the total microcystin concentrations in the competition experiments gradually declined. We did not find evidence for allelopathic interactions, as nontoxic strains became dominant even when toxic strains were given a major initial advantage. These findings show that, in our experiments, nontoxic strains of Microcystis were better competitors for light than toxic strains. The generality of this finding deserves further investigation with other Microcystis strains. The competitive replacement of toxic by nontoxic strains offers a plausible explanation for the gradual decrease in average toxicity per cell during the development of dense Microcystis blooms.

* Corresponding author. Mailing address: Aquatic Microbiology, Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Nieuwe Achtergracht 127, 1018 WS Amsterdam, The Netherlands. Phone: 31 20 5257073. Fax: 31 20 5257064. E-mail: pvisser{at}science.uva.nl

{triangledown} Published ahead of print on 2 March 2007.

{dagger} W.E.A.K. and L.T. contributed equally to this work.

{ddagger} Present address: DHV Consultancy, P.O. Box 1132, 3800 BC Amersfoort, The Netherlands.

§ Present address: National Institute for Public Health and the Environment, P.O. Box 1, 3720 BA Bilthoven, The Netherlands.

Applied and Environmental Microbiology, May 2007, p. 2939-2946, Vol. 73, No. 9
0099-2240/07/$08.00+0     doi:10.1128/AEM.02892-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

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  • Briand, E., Gugger, M., Francois, J.-C., Bernard, C., Humbert, J.-F., Quiblier, C. (2008). Temporal Variations in the Dynamics of Potentially Microcystin-Producing Strains in a Bloom-Forming Planktothrix agardhii (Cyanobacterium) Population. Appl. Environ. Microbiol. 74: 3839-3848 [Abstract] [Full Text]  


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