Biodegradation of microcystin using free and alginate-immobilized Stenotrophomonas geniculate DMC-X3 bacterium

The eutrophication of water bodies and global warming have led to frequent cyanobacterial blooms, producing large quantities of algal toxins, which are released into water bodies, posing a threat to human health. Among known algal toxins, microcystin (MC) is the most harmful and most commonly detected. Because of its stable chemical structure, it is difficult to degrade MC though chemical and physical methods. Hence, effectively removing MC from water and ensuring water safety have become urgent issues. In this study, strain DMC-X3, which could rapidly and efficiently degrade MC, was isolated from a reservoir affected by a Microcystis aeruginosa bloom and identified as Stenotrophomonas geniculate. Inoculated at OD600=0.1, strain DMC-X3 degraded 70% of 1000 μg/L MC in 24 h, and over 90% within 48 h. When the inoculation density was increased to OD600=0.35, this bacterial strain completely degraded 1000 μg/L MC in 16 h and 5000 μg/L MC in 96 h. DMC-X3 maintained its MC degradation ability under the environmental conditions of pH 5–11 and 15–35°C. After 60 d of storage at room temperature, DMC-X3 embedded and immobilized on sodium alginate pellets showed 90% degradation of 200 μg/L MC in 48 h, and the pellets could be used for at least three cycles. Sustained-release pellets made by embedding and immobilizing both the degradation bacteria DMC-X3 and algicidal substance prodigiosin on sodium alginate effectively eradicated M. aeruginosa cells and degraded MC, promising a good application prospect in controlling M. aeruginosa blooms.