Biotransformation and detoxification of saxitoxin by Bacillus flexus in batch experiments

Abstract Saxitoxins (STXs) are carbamate alkaloid neurotoxins produced by some species of cyanobacteria. They are water soluble and relatively stable the natural environment, and thereby represent a risk to animal and human health through a long-time exposure. STXs cannot be sufficiently removed by conventional water treatment methods. Therefore, this study investigates the potential STX biodegradation and detoxification by bacteria as a promising method for toxin removal. STX biodegradation experiments were conducted using Bacillus flexus SSZ01 strain in batch cultures. The results revealed that SSZ01 strain grew well and rapidly detoxified STX, with no lag phase observed. STX detoxification by SSZ01 strain was initial-toxin-concentration–dependent. The highest biotransformation rate (10µg STX L-1 day-1) was obtained at the highest initial toxin concentrations (50µg L-1) and the lowest (0.06µg STX L-1 day-1) was recorded at the lowest initial concentration (0.5µg L-1). STX biotransformation rate increased with temperature, with highest occurred at 30 ºC. This rate was also influenced by pH, with highest obtained at pH8 and lowest at higher and lower pH values. HPLC chromatograms showed that STX biotransformation peak is corresponding to the least STX analogue (disulfated sulfocarbamoyl-C1 variant). The Artemia-based toxicity assay revealed that this biotransformation byproduct was nontoxic. This suggests the potential application of this bacterial strain in slow sand filters for cyanotoxin removal in water treatment plants. Being nontoxic, this byproduct needs to be assayed for its therapeutic effects towards neurodegenerative diseases.