Degradation of the cyanobacterial toxin anatoxin-a by a Bacillus strain in batch culture

Abstract

Abstract Anatoxin-a (ATX-a) is an alkaloid neurotoxin produced by certain species of cyanobacteria. It is water soluble and relatively stable in natural water, and thereby could present health hazards to human, animals and plants through prolonged exposure. Conventional water treatment methods are insufficient for ATX-a removal, and sometimes cause cell lysis and release on intracellular toxin. Biodegradation could be a promising method for removal of this toxin. This study addresses for the first time ATX-a biodegradation by Bacillus strain into a nontoxic byproduct (epioxy-ATX-a). The results showed that Bacillus strain AMRI-03 grew without lag phase in a lake water containing ATX-a.The strain also exhibited rapid ATX-a degradation, and the total degradation was initial- toxin-concentration–dependent.Total degradation of ATX-a occurred within 4 days at the highest two initial concentrations (50 & 100µg L− 1), compared to 6 and 7 days at lower concentrations (20, 10, and 1µg L− 1, respectively). Biodegradation rate by this bacterium also depended on initial ATX-a concentration, with highest value (12.5µg ATX L− 1 day− 1) recorded at the highest initial toxin concentrations (50 & 100µg L− 1). ATX-a biodegradation rate was influenced by temperature, with highest occurred at 25 and 30 ºC. pH also affected this rate, and the highest rates were obtained under neutral and slightly alkaline conditions (i.e., pH7 and 8). Both lower and higher pHs slowed the degradation rate. Being nontoxic, this bacterial strain could be applied in slow sand filters for degradation and removal of anatoxin-a in water treatment plants, after setting up mesocosm experiments to assess the potential effects of this bacterium on water quality.