Jae-Hyoung Joo

Use of immobilized algicidal bacteria to control natural freshwater diatom blooms

The purpose of this investigation was to assess the possible use of algicidal bacteria in conjunction with an immobilization technique for efficient termination of natural blooms of Stephanodiscus concomitant with minimization of adverse effects caused by a single application of bacteria. The performance of Pseudomonas fluorescens cells immobilized on cellulose sponges (CIS) was compared with that of freely suspended cells (FSC) of the organism at low water temperature (WT) of <10°C in co-cultures and natural microcosms. In the co-cultures, CIS resulted in more effective lysis of Stephanodiscus, irrespective of similar bacterivore (Spumella sp.) density, and significantly reduced the concentrations of nitrate and soluble reactive phosphorus (SRP), but not that of silicate, compared with FSC. In the microcosms containing natural freshwater, CIS reduced the densities of Stephanodiscus spp. and Aulacoseira spp. but had no effect on other phytoplankton. Compared with FSC, removal of nutrients by the CIS prevented secondary blooms caused by other phytoplankton. Our results indicate that the CIS affords effective protection of P. fluorescens from low WT and heterotrophs, and restrained regeneration of both SRP and nitrate. Thus, it was demonstrated that the CIS may be an attractive alternative to FSC for control of natural blooms.

Relationship between dissolved organic carbon and bacterial community in the coastal waters of Incheon, Korea

Abstract Bacteria constitute a large domain of prokaryotic microorganisms present in marine ecosystems and play a significant role in energy flow and nutrient cycling. Bacterial community changes may affect organisms of higher trophic levels. We conducted field monitoring to study the relationship between dissolved organic carbon (DOC) and the bacterial community in the coastal waters of Incheon, Korea. Results showed that abiotic factors, such as temperature, salinity, dissolved oxygen (DO), pH, and dissolved inorganic nutrients, were not significantly different among the sampling sites during the study period. On the other hand, nutrient conditions were significantly different among the sites between 2012-2013 and 2014. Nitrogen was the limiting factor from 2012 to 2013, and phosphate in 2014. Biotic data showed that DOC affected both bacterial abundance and bacterial composition. A similar fluctuation pattern was observed for phytoplankton and Chlorophyll a. However, a close correlation was not observed between phytoplankton and other variables. Redundancy analysis (RDA) and Pearson correlation analysis of abiotic and biotic factors also showed that DOC concentration and bacterial abundance were correlated. Therefore, DOC appears to be an important factor affecting bacterial abundance and composition in the coastal waters of Incheon, Korea.

Improvement of cyanobacterial-killing biologically derived substances (BDSs) using an ecologically safe and cost-effective naphthoquinone derivative

In previous studies, naphthoquinone (NQ) compounds have been shown to be effective, selective, and ecologically safe algicides for controlling harmful algal blooming species (HABs) or winter bloom species, such as Stephanodiscus hantzschii. However, there are no reports on NQ-based algicides for use with cyanobacterial blooming species. In this study, we developed 31 NQ compounds to investigate algicides for mitigating cyanobacterial blooms. In addition, to better apply these compounds in the field, we reduced the number of production steps to develop a cost-effective algicide. In preliminary testing, we screened NQ compounds that showed the best algicidal activity on target cyanobacteria, including Aphanizomenon, Dolichospermum, Microcystis, Oscillatoria, and Nostoc species. The compound NQ 2-0 showed the highest algicidal activity (90%) at a low concentration (≥1μM) on target algae. These were very limiting algicidal effects of 1µM NQ 2-0 observed against non-target algae, such as diatoms (Stephanodiscus hantzschii, Cyclotella meneghiniana, Synedra acus, and Aulacoseira granulata) or green algae (Cosmarium bioculatum and Scenedesmus quadricauda), and the effect did not exceed 15-25% (except against S. quadricauda). NQ 2-0 (1μM) showed no eco-toxicity, as represented by the survival rates of Pseudokirchneriella subcapitata (100%), Daphnia magna (100%), and Danio rerio (100%). Additionally, a chronic eco-toxicity assessment showed no toxicity toward the survival, growth or reproduction of D. magna. Moreover, NQ 2-0 quickly dissipated from field water samples and had a half-life of approximately 3.2 days. These results suggest that NQ 2-0 could be a selective and ecologically safe algicide to mitigate harmful cyanobacterial blooms.

Fabrication of Biodegradable Polylactide Foam for Algal Bloom Control

Eutrophication of reservoirs, lakes and rivers is the phenomenon that induces algal blooms by accumulating nutriments in the water system because of the continuous inflow of pollutants such as domestic sewage and industrial wastewater. This phenomenon is a global environmental problem that threatens water systems, coastal ecosystems and even human life. A recent method to solve the problem is the use of scaffolding for releasing algicide. Although this method has the effect of controlling algae, it can cause secondary environmental problems such as toxicity to other species and waste of the used scaffold. In this research, to improve the eco-friendliness and efficiency of the algicide-releasing process, biodegradable polymer foam as a carrier of the algicide was prepared. Polylactide is a biodegradable polymer that can be obtained from natural resources such as cornstarch and tapioca starch. Polylactide foam, which has high porosity and surface area because of its open-cell structure, was produced using the salt-leaching method. The most important property of polylactide foam is controlling the pore size to make it suitable for the size of the algicide. The pore size of polylactide foam is controlled by the size of the used salt particle itself. The pore size and porosity were confirmed by analyzing the morphology of polylactide foam. The algicide was loaded on the polylactide foam using the injection method. A microcosm test of Stephanodiscus was performed to confirm the efficiency of algicide release from the polylactide foam. To investigate the biodegradability of the polylactide foam, an enzymatic degradation test was performed.