Algicidal activity of the bacterium, Pseudomonas fluorescens SK09, to mitigate Stephanodiscus hantzschii (Bacillariophyceae) blooms using field mesocosms

Seong Yu Noh,Seung Won Jung,Baek Ho Kim,Toshiya Katano,Myung-Soo Han

doi:10.1080/02705060.2017.1323682

Abstract

ABSTRACTThe main goal of this study was to characterize mortality and trophic interactions of Stephanodiscus hantzschii (small centric diatoms) in the presence of an algicidal bacterium, Pseudomonas fluorescens HYK0210-SK09 (SK09) in outdoor mesocosm experiments with an extremely low temperature and also in direct application in a river. SK09 at an inoculation density of 5 × 106 cells/mL (Experiment 1) and SK09 cells immobilized in activated carbon polyvinyl alcohol sponge carriers (Experiment 2) did not appear to attack S. hantzschii in a species-specific manner at temperatures close to freezing. Furthermore, SK09 did not control the diatom blooms when SK09 cells immobilized in the carriers were directly applied in the river. The dynamics of both the heterotrophic flagellate and ciliate abundances showed similar trends to the activity of algicidal bacteria; moreover the heterotrophic protists could not control the total bacterial density. Inorganic nutrient concentrations and conductivity remained unchanged compared with those in the control group. The results obtained in this study and previous results are important for assessing biological control using algicidal bacteria in the wild.

Highlights

The small centric freshwater diatom Stephanodiscus hantzschii Grunow is one of the common species causing blooms in winter worldwide (e.g. Kilham et al 1986; Kobanova & Genkal 1989)
The bacteria were immobilized in the carrier as described previously by Jung et al (2009a, 2013): the sterilized cubes of the activated carbon polyvinyl alcohol sponge (APVAS) carrier were placed in 40 L of SK09 cells grown in nutrient broth (NB) medium in log phase to a cell density of over 1010 cells/mL, and incubated for 4 hours at 25 C and stirred at 30 rpm in the dark
The changes in the abundance of S. hantzschii and the maximum algicidal effect (MAE) of SK09 are presented in Tables 2 and 3

Summary

Introduction

The small centric freshwater diatom Stephanodiscus hantzschii Grunow is one of the common species causing blooms in winter worldwide (e.g. Kilham et al 1986; Kobanova & Genkal 1989). In South Korea, S. hantzschii blooms occur annually and can reach a density of over 105 cells/mL during winter in the Han, Nakdong, and Yeongsan rivers (Jung et al 2009b, 2011, 2013; Jeong et al 2014). These diatom blooms have adverse social, economic, and environmental effects, such as low water transparency, unpleasant water odor and taste, as well as clogging of and/or sedimentation in water treatment equipment (Oksiyuk 1965; Lee et al 2001; Kolmakov et al 2002; Hijnen et al 2007).

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