Potential and limitation of algicidal bacteria for controlling natural Stephanodiscus blooms under environmentally realistic exposure conditions

Abstract

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. The field mesocosm were dosed with single application of isolated SK09 and monitored at Samnagjin in the lower part of the Nakdong River (South Korea) during 12 days of the winter season. We found that the tested bacterium acted against some species of Stephanodiscus- and Aulacoseria-like structure on in vitro and in vivo diatom bloom. However, this bacterium failed to fully control in vivo natural blooms of Stephanodiscus owing to the low water temperatures of <10oC and predation activity of protozooplankton (heterotrophic nanoflagellates and ciliates), and its selective inhibition indirectly affected the decrease of dissolved oxygen levels, the dramatic regeneration of N and P by large-scale Stephanodiscus-lysing process and a great increase in algal biomass of genera Chlamydomonas. This strongly suggests that we need to develop an effective strategy for enhancing the activity of algicidal bacteria and for mitigating some drawbacks to effective and safely regulate natural diatom blooms.