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Active release of microcystins controlled by an endogenous rhythm in the cyanobacterium Microcystis aeruginosa

Authors

  • Micheline Kézia Cordeiro-Araújo,

    1. Department of Biological Sciences, Luiz de Queiroz College of Agriculture, University of São Paulo, Piracicaba, Brazil
    2. Graduating Program on Botany, Rural and Federal University of Pernambuco, Recife, Brazil
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  • Maria do Carmo Bittencourt-Oliveira

    Corresponding author
    1. Graduating Program on Botany, Rural and Federal University of Pernambuco, Recife, Brazil
    • Department of Biological Sciences, Luiz de Queiroz College of Agriculture, University of São Paulo, Piracicaba, Brazil
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  • Communicating Editor: H. Miyashita.

To whom correspondence should be addressed.

Email: mbitt@usp.br

Summary

The active release of microcystins in cyanobacterium Microcystis aeruginosa (Kützing) Kützing, strain BCCUSP232 was confirmed. The microcystin release is controlled by an endogenous rhythm, pointing to a biosynthetic pattern of toxins in cyanobacteria. Proofing tests for this active release were carried out by experiments at two independent 24 h cycles, light : dark and continuous light (12:12 h) along the exponential growing phase. Cultivation samples at light, temperature and photoperiod controlled conditions were collected in 2-h intervals. Microcystin concentrations from the pellet aliquots (intracellular microcystin per cell-quota –IMC) and supernatant (extracellular microcystin per equivalent cell-quota – EMC) were quantified with enzyme linked immunosorbent assay. The IMC concentrations showed increases and decreases in both cycles. Decreases of IMC clearly demonstrate that the toxin was actively released to the surrounding medium and not by cell lysis. The total microcystins concentrations (IMC and EMC) between the light : dark and continuous light cycles presented similar variations between the same hours.

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