Comparison of bioactivity of 3 strains of non-toxic Microcystis (Cyanobacteria) grown in different culture media
2006
Victory, K.J. | Lewis, D.M. | Thomas, C.J. | Kumar, M. | King, K.D.
Nutrient bioavailability exerts a significant impact on the production of secondary metabolites by cyanobacteria. The presence of an essential nutrient in a particular form will dictate whether it can be utilized by cells for growth and metabolic functions. The synthesis of bioactive compounds will be influenced by the availability of nutrients within the growth medium. In this study we have examined the growth characteristics and antimicrobial activity of three strains of non-toxic Microcystis cultured under controlled laboratory conditions. All strains were grown in nutrient-rich BG-II, water collected from the River Torrens (Adelaide), and River Torrens water enriched with nitrate, phosphate and Fe-EDTA. Cultures were grown in triplicate in shake flasks at 24 deg C, with mild agitation under a 14:10 hr light/dark cycle. Growth of cultures was assessed by monitoring absorbance at 675 nm. Stationary phase cultures were harvested by centrifugation and freeze-dried to lyophilize the biomass. Cell pellets were extracted with 75% v/v methanol. Extracts were assessed for evidence of growth inhibition of Staphylococcus aureus, Escherichia coli and Bacillus subtilis using an agar disc diffusion assay. Extracts were also tested for antiviral activity against viruses, including dengue virus. All strains demonstrated higher growth rates in BG-II media compared to media prepared from river water. However, M. aeruginosa (Bolivar isolate) exhibited a higher growth rate than other Microcystis isolates when grown in media prepared from Torrens water, regardless of nutrient enrichment. Extracts prepared from these field isolate cells are inhibitory for S. aureus. No extract was found to be toxic to mammalian cells. The authors are currently comparing the bioactivity of Microcystis cultures grown under different conditions as a prelude to large-scale production.
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