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Applied and Environmental Microbiology, February 2003, p. 787-795, Vol. 69, No. 2
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.2.787-795.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

The Abundance of Microcystin-Producing Genotypes Correlates Positively with Colony Size in Microcystis sp. and Determines Its Microcystin Net Production in Lake Wannsee

Rainer Kurmayer,1,2* Guntram Christiansen,3 and Ingrid Chorus1

Federal Environmental Agency, 14195 Berlin,1 Institute for Biology (Genetics), Humboldt University, 10115 Berlin, Germany,3 Institute for Limnology, Austrian Academy of Sciences, 5310 Mondsee, Austria2

Received 24 July 2002/ Accepted 14 November 2002

The working hypotheses tested on a natural population of Microcystis sp. in Lake Wannsee (Berlin, Germany) were that (i) the varying abundance of microcystin-producing genotypes versus non-microcystin-producing genotypes is a key factor for microcystin net production and (ii) the occurrence of a gene for microcystin net production is related to colony morphology, particularly colony size. To test these hypotheses, samples were fractionated by colony size with a sieving procedure during the summer of 2000. Each colony size class was analyzed for cell numbers, the proportion of microcystin-producing genotypes, and microcystin concentrations. The smallest size class of Microcystis colonies (<50 µm) showed the lowest proportion of microcystin-producing genotypes, the highest proportion of non-microcystin-producing cells, and the lowest microcystin cell quotas (sum of microcystins RR, YR, LR, and WR). In contrast, the larger size classes of Microcystis colonies (>100 µm) showed the highest proportion of microcystin-producing genotypes, the lowest proportion of non-microcystin-producing cells, and the highest microcystin cell quotas. The microcystin net production rate was nearly one to one positively related to the population growth rate for the larger colony size classes (>100 µm); however, no relationship could be found for the smaller size classes. It was concluded that the variations found in microcystin net production between colony size classes are chiefly due to differences in genotype composition and that the microcystin net production in the lake is mainly influenced by the abundance of the larger (>100-µm) microcystin-producing colonies.

* Corresponding author. Mailing address: Austrian Academy of Sciences, Institute for Limnology, Mondseestraße 9, 5310 Mondsee, Austria. Phone: 43 6232 3125 32. Fax: 43 6232 3578. E-mail: rainer.kurmayer{at}oeaw.ac.at.

Applied and Environmental Microbiology, February 2003, p. 787-795, Vol. 69, No. 2
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.2.787-795.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



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