Simultaneous <i>Microcystis</i> Algicidal and Microcystin Degrading Capability by a Single <i>Acinetobacter</i> Bacterial Strain

Abstract

Measures for removal of toxic harmful algal blooms often cause lysis of algal cells and release of microcystins (MCs). In this study, Acinetobacter sp. CMDB-2 that exhibits distinct algal lysing activity and MCs degradation capability was isolated. The physiological response and morphological characteristics of toxin-producing Microcystis aeruginosa, the dynamics of intra- and extracellular MC-LR concentration were studied in an algal/bacterial cocultured system. The results demonstrated that Acinetobacter sp. CMDB-2 caused thorough decomposition of algal cells and impairment of photosynthesis within 24 h. Enhanced algal lysis and MC-LR release appeared with increasing bacterial density from 1 × 10³ to 1 × 10⁷ cells/mL; however, the MC-LR was reduced by nearly 94% within 14 h irrespective of bacterial density. Measurement of extracellular and intracellular MC-LR revealed that the toxin was decreased by 92% in bacterial cell incubated systems relative to control and bacterial cell-free filtrate systems. The results confirmed that the bacterial metabolite caused 92% lysis of Microcystis aeruginosa cells, whereas the bacterial cells were responsible for approximately 91% reduction of MC-LR. The joint efforts of the bacterium and its metabolite accomplished the sustainable removal of algae and MC-LR. This is the first report of a single bacterial strain that achieves these dual actions.