The role of genus Bacillus in biodegradation of microcystins: Implications for the removal of cyanotoxins from tropical freshwaters

Abstract

The proliferation of harmful cyanobacterial blooms poses a threat to the ecosystem and human health. Microcystins (MCs) are the most frequently detected cyanotoxin released by cyanobacteria, including Microcystis sp. Our study aimed to isolate potential MC-degrading bacteria in Sri Lankan freshwater and determine their possible MC-degradation pathways. Twenty-two morphologically distinct bacterial strains from 13 freshwater bodies were isolated following the enrichment assay. MC-biodegradation assays further confirmed the MC-degradation potential of 21 strains, with Bacillus being the predominant genus. The strain Bacillus altitudinis BL1, isolated from Beira Lake, showed the highest efficiency in Microcystis sp. cell lysis (80%) and MC-degradation (87%). PCR assay results confirmed the absence of mlrABCD genes in all strains, indicating the presence of uncharacterized alternative MC-degradation mechanisms that require further exploration. The dual functions of Microcystis sp. cell lysis and MC-degradation in 21 strains support developing efficient bacteria-mediated strategies to remediate microcystins and eradicate Microcystis-blooms in tropical freshwaters.