In situ bacterial mitigation of the toxic cyanobacterium Microcystis aeruginosa: implications for biological bloom control

Abstract

The algicidal bacterium Xanthobacter autotrophicus HYS0201‐SM02 (SM02) was isolated from the surface water of a eutrophic lake (Lake Daechung, Korea). In vivo and in situ experiments showed that SM02 had algicidal activity against both a cultured strain and natural colonial morphs of the toxic cyanobacterium, Microcystis aeruginosa. Both the SM02 bacteria and its culture filtrate showed anti‐algal activity against M. aeruginosa, indicating that an algicidal substance was released from SM02. The threshold concentration of SM02 for maximal algicidal activity against a natural bloom of M. aeruginosa was 107 CFU/mL. In situ co‐culture of SM02 and M. aeruginosa showed that SM02 did not benefit from the massive decay of M. aeruginosa. In fact, repeated inoculations with a low concentration of SM02 were required for optimal algicidal activity, suggesting that water quality worsened during co‐culture (i.e., nutrients and microcystin‐LR concentration increased). These results suggest a role for the algicidal bacterium X. autotrophicus SM02 in biorestoration but probably not in treating outdoor Microcystis blooms. When developing a biological agent to control M. aeruginosa blooms in the field, it will be important to screen for specific agents with low threshold concentrations and high algicidal activity.