Simultaneous biodegradation of harmful Cylindrospermopsis raciborskii and cylindrospermopsin toxin in batch culture by single Bacillus strain

Abstract

This study investigates the capability of a Bacillus exus 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 ltrate. Living bacterial cells inhibited C. raciborskii growth after 2 days of incubation with complete cell death at day 5. Bacterial ltrate caused a rapid reduction in C. raciborskii growth at the rst day, with complete cell lysis at day3. 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 lters would give possibilities for degradation and bioremediation of cyanotoxins in drinking water treatment plants.

Biotransformation and detoxification of saxitoxin by Bacillus flexus in batch experiments

“…Strain SSZ01 grew well and showed no lag phase in the presence of STX in bacterial cultures. The absence of lag phase was also observed during CYN biodegradation by this strain (Mohamed et al 2022). These results support the hypothesis that biodegradation of cyanotoxins takes place rapidly by bacterial strains with a previous history of these toxins in the aquatic environment (Smith et This apparently the most common feature of the biodegradation of many organic pollutants.…”

“…It was identi ed by 16S rRNA gene analysis and deposited in the Gene bank with an accession of GU112451 (Alamri 2012). The strain was found to degrade other cyanotoxins such as microcystin and cylindrospermopsin (Alamri 2012;Mohamed et al 2022). STX was purchased from Abraxis (Warminster, PA, USA).…”

“…al. 2008; Mohamed and Alamri 2012;Mohamed et al 2022). By co-existing with toxic cyanobacterial blooms in the same environment, our strain could have been frequently exposed to this toxin produced by cyanobacteria.…”

“…As a result, an e cient cost-effective and eco-friendly methods of cyanotoxin elimination are required. In this respect, it has been reported that biodegradation is cost effective method with low risk for removing cyanotoxins from water (Mohamed and Alamri 2012;Li et al, 2015;Lezcano 2016;Mohamed et al 2022). However, little is known about biodegradation and biotransformation of STXs by bacteria, compared to microcystin and cylindrospermopsin.…”

“…Donovan et al (2008) has also demonstrated the biodegradation of STXs by seven unidenti ed marine bacteria, isolated from the digestive tract of blue mussels. Taken that Bacillus exus was referred as an environment-friendly bioagent for elimination of arsenic and other pollutants from wastewater (Jebeli et al 2017) and its capability for degradation of microcystin and cylindrospermopsin toxins (Alamri 2012;Mohamed et al 2022), it could also have the potentiality to degrade STXs in aquatic environment. Hence, the present study adopted the evaluation of biodegradation capability of STXs by Bacillus exus SSZ01 strain isolated from decayed cyanobacterial blooms in a eutrophic Saudi lake (Alamri 2010).…”