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Applied and Environmental Microbiology, January 2001, p. 278-283, Vol. 67, No. 1
0099-2240/01/$04.00+0   DOI: 10.1128/AEM.67.1.278-283.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Cellular Microcystin Content in N-Limited Microcystis aeruginosa Can Be Predicted from Growth Rate

Benedict M. Long,1 Gary J. Jones,2,* and Philip T. Orr2

Department of Botany, La Trobe University, Victoria 3086,1 and CSIRO Land and Water, Indooroopilly, Queensland 4068,2 Australia

Received 25 May 2000/Accepted 11 October 2000

Cell quotas of microcystin (QMCYST; femtomoles of MCYST per cell), protein, and chlorophyll a (Chl a), cell dry weight, and cell volume were measured over a range of growth rates in N-limited chemostat cultures of the toxic cyanobacterium Microcystis aeruginosa MASH 01-A19. There was a positive linear relationship between QMCYST and specific growth rate (µ), from which we propose a generalized model that enables QMCYST at any nutrient-limited growth rate to be predicted based on a single batch culture experiment. The model predicts QMCYST from µ, µmax (maximum specific growth rate), QMCYSTmax (maximum cell quota), and QMCYSTmin (minimum cell quota). Under the conditions examined in this study, we predict a QMCYSTmax of 0.129 fmol cell-1 at µmax and a QMCYSTmin of 0.050 fmol cell-1 at µ = 0. Net MCYST production rate (RMCYST) asymptotes to zero at µ = 0 and reaches a maximum of 0.155 fmol cell-1 day-1 at µmax. MCYST/dry weight ratio (milligrams per gram [dry weight]) increased linearly with µ, whereas the MCYST/protein ratio reached a maximum at intermediate µ. In contrast, the MCYST/Chl a ratio remained constant. Cell volume correlated negatively with µ, leading to an increase in intracellular MCYST concentration at high µ. Taken together, our results show that fast-growing cells of N-limited M. aeruginosa are smaller, are of lower mass, and have a higher intracellular MCYST quota and concentration than slow-growing cells. The data also highlight the importance of determining cell MCYST quotas, as potentially confusing interpretations can arise from determining MCYST content as a ratio to other cell components.

* Corresponding author. Mailing address: CRC for Freshwater Ecology, University of Canberra, Building 15, Canberra, ACT 2601, Australia. Phone: 61 2 6201 5168. Fax: 61 2 6201 5038.

Applied and Environmental Microbiology, January 2001, p. 278-283, Vol. 67, No. 1
0099-2240/01/$04.00+0   DOI: 10.1128/AEM.67.1.278-283.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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