Biodegradation of cylindrospermopsin toxin by microcystin-degrading bacteria isolated from cyanobacterial blooms.

Cylindrospermopsin (CYN) is highly water soluble and stable cyanotoxin which can persist in water sources and pose health hazards to human, animals and plants. Consequently, there is a need to fully understand the fate of CYN in the aquatic environment, in particular, its biodegradation by endemic organisms. Although there is evidence of CYN degradation by microbial population, bacterial strains responsible for the toxin degradation are not yet identified. This study reports for the first time CYN degradation by Bacillus strain (AMRI-03) isolated from cyanobacterial blooms. In degradation batch experiment, the strain grew well in the presence of CYN without showing any lag period, and this growth increased with the initial CYN concentration. CYN degradation occurred rapidly, and the complete degradation was dependent on the initial CYN concentration. It occurred after 6 days at the highest concentration (300 μg L(-1)) compared to 7 and 8 days at lower concentrations (10 & 100 μg L(-1)). Also, the degradation rate correlated positively with the initial CYN concentration with maximum value (50 μg L(-1) day(-1)) obtained at the highest CYN concentration. Furthermore, the biodegradation rate of CYN by this strain depended remarkably on temperature and pH. The highest biodegradation rates were obtained at 25 and 30 °C, and at pH 7 and pH 8. Taken that such microcystin-degrading strain can also degrade CYN, bacterial strains reported worldwide as microcystin degraders could be tested for their capability of CYN degradation.