Biodegradation of the cyanotoxin cylindrospermopsin by Bacillus cereus, Micrococcus luteus and Alcaligenes faecalis

Abstract

Cylindrospermopsin (CYN) is a cyanotoxin found in natural waters, with potential risk to human health through the inhibition of protein synthesis. Despite the implementation of conventional water treatment procedures, complete removal of CYN remains a question due to its heat-stable nature. Hence, contamination of water sources with CYN is a challenge in providing safe drinking water throughout the world. The present study was conducted to test the ability to degrade CYN at 280C and pH 7, of four bacterial strains: Bacillus cereus-Y, Bacillus cereus-S (B. cereus-S), Micrococcus luteus, and Alcaligenes faecalis, which were previously isolated from different water sources as different hydrocarbon degraders. The CYN degradation kinetics of each bacterial species were studied using High Performance Liquid Chromatography. The greatest CYN degradation (28.22 ± 0.24%) was shown by the bacterium B. cereus-S in 5.0 mg/L CYN within 14 days. The CYN degradation by the other strains was lower than 10% under the same conditions. Further studies employing different initial concentrations of CYN revealed that B. cereus-S could degrade lower CYN concentrations at a higher percentage (1.0 mg/L, 2.5 mg/L, and 5.0 mg/L of CYN removal percentages were 36.83 ± 2.43%, 32.25 ± 1.25%, and 24.72 ± 0.40%, respectively, after 14 days of incubation at 280C and pH 7). The maximum average degradation rates were recorded for 1.0 mg/L, 2.5 mg/L, and 5.0 mg/L CYN on the 6th (0.05 ± 0.00 mg/L/day), 8th (0.04 ± 0.01 mg/L/day), and 12th (0.02 ± 0.01 mg/L/day) days of incubation, respectively. The study showed the potentiality of the bacterium B. cereus-S on the application for degrading CYN among the tested bacteria species.