Abstract
This study investigates the capability of a Bacillus flexus strain isolated from decayed cyanobacterial blooms for the bioremediation of Cylindrospermopsis raciborskii and cylindrospermopsin (CYN) toxin. The algicidal activity of this strain was tested by co-cultivation with C. raciborskii cultures. CYN biodegradation was investigated in the presence of living and heat-inactivated bacterial cells or bacterial filtrate. Living bacterial cells inhibited C. raciborskii growth after 2 days of incubation with complete cell death at day 5. Bacterial filtrate caused a rapid reduction in C. raciborskii growth at the first day, with complete cell lysis at day 3. Only living cells of SSZ01 caused reduction in CYN released into the medium during the bacterial decay of C. raciborskii cells. The biodegradation rate of CYN by SSZ01 relied on initial toxin concentrations. The highest rate (42 μg CYN L-1 day-1) was obtained at the higher initial concentration (300 μg L-1), and the lowest (4μg CYN L-1 day-1) was at lower concentration (50 μg L-1). These results suggest that this bacterial strain could be employed to bioremediate cyanobacterial blooms in freshwaters. Also, the application of this bacterium in slow sand filters would give possibilities for degradation and bioremediation of cyanotoxins in drinking water treatment plants.
Highlights
Harmful cyanobacterial blooms (HCBs) seriously threaten the environmental and human health
The cell density of C. raciborskii cocultivated with living bacterial cells increased in the first 2 days, and subsequently decreased and all cyanobacterial cells lysed by day 5 (Fig .1)
The strongest inhibition of cyanobacterial growth occurred at initial bacterial concentration of 106, which caused complete cell lysis by day 5, but the weakest inhibition occurred at initial concentration of 103, which caused no complete death of cyanobacterial cells (Fig.2)
Summary
Harmful cyanobacterial blooms (HCBs) seriously threaten the environmental and human health. Most cyanobacterial blooms are constituted by toxin-producing species which damage the aquatic ecosystem and impair the safety of drinking water (Mohamed et al.2015). The toxin exhibits a high persistent in different water environments because of its chemical stability and slow degradation (Wormer et al 2008). This trait is of a particular concern for water authorities for controlling Cylindrospermopsis growth and removing CYN toxin from drinking and irrigation waters
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