Field assessment of the potential of algicidal bacteria against diatom blooms

The possible use of algicidal bacteria for the efficient termination of natural freshwater diatom blooms with minimal adverse effects on the freshwater ecosystem was assessed under laboratory and field conditions. A field mesocosm (150 L) was dosed with a single application of isolate SK09, and monitored at Samnang jin in the lower part of the Nakdong River (South Korea) over 12 days of the winter season. We found that the tested bacterium acted against some species of Stephanodiscus-and Aulacoseira-like structures on in vitro and in vivo diatom blooms. However, this bacterium failed to fully control in vivo natural blooms of Stephanodiscus due to the low water temperatures of less than 10 degrees C and predation activity of protozooplankton (heterotrophic nanoflagellates and ciliates). In addition, its selective inhibition indirectly affected the decrease of dissolved oxygen levels, the dramatic regeneration of N and P by the large-scale Stephanodiscus-lysing process, and a great increase in algal biomass of genera Chlamydomonas. This strongly suggests the necessity of developing an effective strategy for enhancing the activity of algicidal bacteria, and for mitigating some drawbacks to effectively and safely regulate natural diatom blooms.