A bacterium capable of degrading microcystin-RR (MC-RR) was isolated from a Saudi eutrophic lake which was previously reported to have microcystin-producing cyanobacteria. Based on the analysis of the 16S rRNA gene sequence, the isolated strain SSZ01, most likely belong to the genus Bacillus with a highest sequence similarity (99%) with Bacillus flexus strain EMGA5. It was found that B. flexus strain SSZ01, possesses an mlrA gene encoding the most important enzyme for MC degradation. This strain was capable of degrading MC-RR, at a concentration of 10 mg l(-1), in batch experiments under environmentally relevant conditions. The degradation of MC-RR was completely removed within 4 d. The degradation of MC-RR by this strain occurred in a rich medium nutrient broth (NB), indicating that this could likely occur along with other organic compounds found in the environment. Therefore, the coexistence of such bacteria with MCs in the same environment can contribute to the self-purification of the ecosystem from such potent toxins. This is the first study to report that B. flexus can degrade MCs.
Keywords: 16S rRNA gene; Bacillus; Biodegradation; Microcystins; mlrA gene.