Botany Department, Faculty of Science, Tanta University, Egypt E. Mail: mostafaelsheekh@yahoo.com.
Correspondence Author.
1 Hydrobiology Lab., National Institute of Oceanography and Fisheries, Alexandria, Egypt.
In this study, we investigated the allelopathic effects of cyanobacterium Microcystis aeruginosa Kützing, on monocultures of phytoplankton [Oscillatoria angutissima West & West; Anabaena PCC.7120, Scendesmus obliquus (Turpin) Kützing and Chlorella vulgaris Beijerinck]. The allelopathic effects of cell-free filtrates of M. aeruginosa were determined on growth and pigments content (chlorophyll-a, b and carotenoides) at 0,3,7 and 14 days after incubation. The concentrations of microcystin-LR inside the cells of M. aeruginosa were determined by HPLC during log, stationary and retardation phases of growth and the toxicity was determined in Artemia salina bioassay. Some chemicals (total carbohydrates, protein, phenolic compounds, alkaloids and fatty acids) were also estimated in the M. aeruginosa cell free media during Log and Retardation phases. The HPLC results showed that microcystin-LR concentrations were 65.6, 1.2 and 0.8 μg.g−1 during the log, stationary and retardation phases of growth, respectively. The effective concentration to inhibit the brine shrimp (Artemia salina) growth by 50% (LC50) 24 h after incubation during the three growth phases was 1.96, 2.4 and 2.61μg.ml−1, respectively. The cell free filtrate of M. aeruginosa from the retardation phase caused maximum reduction in growth and photosynthetic pigments of all tested phytoplankton. The M. aeruginosa crude toxin extract inhibited the growth and chlorophyll-a content of four algal test species. These interactions (allelopathic and stimulatory), probably play a significant role in the succession of algal blooms in nature.
Allelopathy, Anabaena PCC.7120, Artemia salina, Chlorella vulgaris, HPLC, Microcystin LR, Microcystis aeruginosa, Oscillatoria angutissima, Scendesmus obliquus, toxins
