Increased production of extracellular polysaccharides in Arthrospira platensis as a protective response against saxitoxin: Implications to outdoor mass production

Cyanobacteria of both toxic and nontoxic species frequently coexist and thrive in the same habitat. However, little is known about how nontoxic species can mitigate the negative impacts of the toxins produced by toxic species. The current study examined the potential adaptive response of Arthrospira platensis to saxitoxin (STX) in batch cultures. This cyanobacterium was exposed to various STX concentrations for seven days, and growth and antioxidative biomarkers were observed. During the first two days of incubation, the growth (i.e., cell density and chlorophyll-a) dramatically decreased in STX-treated cultures compared to control. Glutathione-S-transferase (GST), superoxide dismutase (SOD), and lipid peroxidation levels increased along with this decline in growth in STX-treated cultures. These parameters were restored to control values on day 3 of incubation and remained at levels that were relatively close to those of control cultures during the remaining period of experiment. The changes in these parameters were associated with the amount of extracellular polysaccharides (EPS) released into the media of STX-treated cultures, demonstrating the role of this EPS in protecting A. platensis cells from this toxin. The results of isotherm experiments confirmed the ability of the released EPS to adsorb STX onto their surfaces, with adsorption capacity (k = 2.9) comparable with that of activated carbon (k = 3.6). This suggests that A. platensis used EPS to build a defense mechanism to limit STX uptake into its cells. This EPS can give A. platensis the advantage of growing in natural lake water in outdoor systems for mass production without experiencing any negative effects from STX. Additionally, EPS could be used in drinking water and wastewater treatment facilities as an ecofriendly adsorbent for saxitoxin and other positively charged cyanotoxins. •Arthrospira platensis can combat STX stress by EPS production•A. platensis released much more EPS in the presence of STX•The released EPS had high capacity for adsorption of STX onto their surfaces.•EPS could also be utilized as ecofriendly adsorbent for saxitoxin from water