Microcystin quota, cell division and microcystin net production of precultured Microcystis aeruginosa CYA 228 (Chroococcales, Cyanophyceae) under field conditions

Abstract

AbstractThe relationship between the specific cell division rate (μc), the specific microcystin (mcyst) production rate (μmcyst) and the cellular content of mcyst (μmcyst) was investigated during growth of Microcystis aeruginosa strain CYA 228 cells in the field (microcosms), and the results were compared with previous data obtained from batch cultures. Growth of an easily recognizable unicellular culture alga in the field made it possible to evaluate different ways of expressing mcyst field data as the ratio of mcyst to dry weight, protein or chlorophyll a (Chl a) against the mcyst quota. The population of CYA 228 cells increased from day 1 to day 7, but decreased from day 7 to day 1 7. More than a threefold variation was observed in Qmcyst of M. aeruginosa cells under field conditions, which indicates that the relationship between μc and μmcyst was not strictly linear. The data from the present experiment support the hypothesis of a constitutive mcyst net production. The average Qmcyst of cells grown under field conditions was 85.7 ± 43.6 (x̄ ± s) fg mcyst cell−1 compared to the average of 278 ± 115 (x̄ ± s) fg mcyst cell−1 found previously under laboratory conditions. The less favourable light conditions during the field study probably caused the reduction in mcyst quota. The data highlight the importance of determining mcyst quotas or the ratio of mcyst to Chl a, because confusing interpretations arise from determining the gravimetric mcyst content or mcyst: protein ratios in the field.