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 su ciently removed by conventional water treatment methods. Therefore, this study investigates the potential STX biodegradation and detoxi cation by bacteria as a promising method for toxin removal. STX biodegradation experiments were conducted using Bacillus exus SSZ01 strain in batch cultures. The results revealed that SSZ01 strain grew well and rapidly detoxi ed STX, with no lag phase observed. STX detoxi cation 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 in uenced 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 lters for cyanotoxin removal in water treatment plants. Being nontoxic, this byproduct needs to be assayed for its therapeutic effects towards neurodegenerative diseases.

Photochemical Degradation of Saxitoxins in Surface Waters

“…While past research has suggested that saxitoxins are not susceptible to biodegradation, ,− recent work has identified bacterial strains capable of degrading the toxins. A new study found that saxitoxins were degraded into nontoxic products by the SSZ01 strain of Bacillus flexus . Another recent study demonstrated that bacterioplankton from a Denmark lake reduced concentrations of STX and analogues by 42–59% .…”

Microbial community structures and bacteria-Cylindrospermopsis raciborskii interactions in Yilong Lake

“…For instance, Bacillus cereus L7 and Lysobacter sp. SG-3 can lyse C. raciborskii cells; also, Bacillus flexus SSZ01 can inhibit C. raciborskii growth and degrade CYN (Flaherty et al 2007 , Hu et al 2023 , Mohamed et al 2023 ). However, compared with other bacteria-algae interaction studies, the diversity of C. raciborskii- interacting bacteria, as well as the mechanisms behind it and the ecological impacts, require further examination.…”