Biological control of Stephanodiscus hantzschii (Bacillariophyceae) blooms in a field mesocosm by immobilized algicidal bacteria Pseudomonas fluorescens HYK0210-SK09

Abstract

The aim of the study was to determine the activity of an immobilized algicidal bacterium, Pseudomonas fluorescens HYK0210-SK09 (SK09), against blooms of Stephanodiscus hantzschii and to characterize its effect in an ecosystem. To this end, SK09 cells that had been immobilized using an activated carbon polyvinyl alcohol sponge (APVAS) were tested in a field mesocosm in the Nakdong River, South Korea. Immobilized SK09 cells showed species-specific activity towards S. hantzschii throughout the study, whereby up to 72% of the population of this species was killed. The APVAS carrier absorbed nutrients in the mesocosms effectively, which reduced the free concentrations of nutrients. Other phytoplankton species, such as Cryptomonas ovata, did not show any fluctuation in abundance. The abundance of heterotrophic protists, such as heterotrophic flagellates and ciliates, increased significantly owing to the utilization of SK09 as a food source. The high level of algicidal activity of SK09 against S. hantzschii was sustained by release of these algicidal cells from the carrier. Thus, the immobilization of algicidal bacteria has various advantages, which include high packing ability, enhancement of bacterial growth, protection of bacterial cells predators, effective nutrient removal, and improved algicidal activity. The present study demonstrates that immobilized SK09 is an effective biocontrol ag