Simultaneous changes in cell quotas of microcystin, chlorophyll a, protein and carbohydrate during different growth phases of a batch culture experiment with Microcystis aeruginosa

The cell quotas of microcystin (Qmcyst), protein (Qprot), chlorophyll a (Qchloro) and carbohydrate (Qcarbo), as well as the net production rates of these parameters, were determined during the exponential and stationary phases in nine batch cultures of Microcystis aeruginosa (CYA 228) at light regimes from 33 to 53 μmol photons m−2 s−1. The following results were obtained. (i) A parallel pattern was found in the changes of Qmcyst, Qprot, Qchloro and Qcarbo during the entire growth cycle and significant correlations were recorded between Qmcyst and Qprot, Qchloro and Qcarbo. (ii) The net microcystin production rate (μmcyst) was positively correlated with the specific cell division rate (μc), the chlorophyll production rate (μchloro) and the protein production rate. (iii) A significant inverse linear relationship was found between μc and Qmcyst, i.e. cultures with a positive μc had a Qmcyst between 110 and 400 fg microcystin cell−1, while declining cultures had Qmcyst values >400 fg microcystin cell−1. Maximum variation in Qmcyst within cultures was 3.5-fold. Collectively, the results show that cells produced microcystin at rates approximating those needed to replace losses to daughter cells during division and that microcystin was produced in a similar way to protein and chlorophyll, indicating a constitutive microcystin production.