Fate of the Toxic Cyclic Heptapeptides, the Microcystins, from Blooms of Microcystis (Cyanobacteria) in a Hypertrophic LAKE1 (original) (raw)

Live cultures of the toxic MicrocY.l'fis viridis (A. Brown) Lemmermann (Chroococcales, Cyanobacteria) were inoculated as prey into cultures of the mixotrophic chrysomonad POferioochromonas malhamensis (Pringsheim) Peterfi (Ochromonadales. Chrysophyceae). POferioochromonas malhamensis ingested and digested all of the prey cells within 5 days. Analysis of the microcystin content in the filtered culture medium and the harvested P. malhamensis cells showed almost all the microcystin in filtered culture medium and never in the chrysomonad cells. Similar results were obtained when lyophilized, cultured samples of M. viridis were inoculated into P. malhamensis cultures. However, when lyophilized samples of a natural toxic cyanobacterial bloom were added as prey to P. malhamensis cultures , 53% of the microcystin concentration was detected in the filtered culture medium and 14.4% in the P. malhamensis cells. The remaining 32.6% may have been degraded by associated heterotrophic bacteria after excretion into the culture medium. It is concluded that almost all of the microcystins are excluded from the chrysomonad cells immediately after release into the food vacuole. Microcystins may be released into lake water not only by bacterial decomposition of toxic cyanobacterial cells but also during grazing and digestion by mixotrophic chrysomonads. * Dedicated to Professors Tadao Yoshida and Masakazu Tatewaki on the occasion of their academic retirement.