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) by D. rotans were observed when they were fed the most toxic of the 5 Microcystis strains, M. aeruginosa NIER-10001. These results suggest that D. rotans has a high tolerance to M. aeruginosa and may undergo microcystin-mediated growth.KEY WORDS: Algivores · Heterotrophic flagellates · Diphylleia rotans · Microcystis spp. · Microcystin-mediated growth · Ingestion Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 45: [163][164][165][166][167][168][169][170] 2006 examined the ecophysiology of this flagellate on its prey using comparisons of grazing behavior on toxic and non-toxic Microcystis strains, along with other algal strains, which represent different food types and qualities. MATERIALS AND METHODSIsolation and culture of the heterotrophic flagellate. Furuike Pond (33°49' 21'' N, 132°48' 04'' E; altitude 40 m) is an impoundment located in Sancho, Matsuyama City, Ehime Prefecture, Japan. It has a surface area of 7400 m 2 and a maximum depth of 1.5 m. The pond is hypereutrophic due to anthropogenic loading from the watershed (Nakano et al. 2001b) and is heavily populated by cyanobacteria, such as Microcystis aeruginosa and M. wesenbergii, from early summer to fall each year (Manage et al. 1999).For isolation of a flagellate capable of grazing on Microcystis species, Microcystis aeruginosa NIES-298 was incubated in Cytophaga broth (CB) medium (MCC-NIES; www.nies.go.jp/biology/mcc/home_j.htm) and mixed with a pond water sample that had been filtered through a Nitex net (mesh size, 154 µm) for removal of larger zooplankton. This mixture was incubated at 25°C in the dark for 3 to 4 d. Flagellates were isolated using a Pasteur micropipette under a light microscope. We established a monoclonal flagellate culture using a repetitive serial isolation process consisting of enrichment, dilution and single cell isolation steps. The isolated flagellate was maintained using a commercial strain of Chlorella TM (Aquanet) as prey. Water was collected from the Pal'tang Reservoir, Korea, filtered through a Whatman GF/F filter and sterilized in an autoclave to yield filtered sterilized water (FSW). A quantity of Chlorella TM was suspended in the FSW, and the flagellate was inoculated into the Chlorella TM suspension. We maintained the flagellate strain by inoculating it weekly into new Chlorella TM suspensions. Incubations were performed at 25°C under a light intensity of 40 to 45 µE m -2 s -1 of cool white fluorescent light, with a 12:12 h light:dark photoperiod.To identify the flagellate, we used light and epifluorescence microscopy and 18S rDNA sequencing. Morphological observations, including the presence of 2 long apical and equal flagella inserting near the anterior end at the top of the ventral groove formed by the curving lateral margins of the cell, a cell dimension of 15 × 20 µm (subject to change during feeding), and feeding observations such as free movement or rotation during feeding via the ventral groove, identified the flagellate as Diphylleia rotans (Massart 1920...

-The diatoms are an ecologically important group of algae that have been extensively studied by ecologists and taxonomists. However, the large-scale patterns of diatom distribution and the factors underlying this distribution are largely unknown. The aims of this study were to identify the large-scale spatial patterns of benthic diatom assemblages in Korean streams and rivers, and to assess the importance of numerous environmental factors on diatom distribution. We classified 720 study sites based on diatom flora. Benthic diatoms, water chemistry, altitude, and riparian land cover and use were characterized by multivariate analyses, Monte Carlo permutation tests, and indicator species analysis. In total, we identified 531 diatom taxa. Diatom assemblages were mostly dominated by species of the genera Achnanthes, Navicula, Nitzschia, Cocconeis, Fragilaria (Synedra included), Cymbella, Gomphonema, and Melosira. Cluster analysis partitioned all 720 sites into eight groups based on diatom species composition. Canonical correspondence analysis indicated that altitude, land cover and use, current velocity, electrical conductivity, and nutrient levels explained a significant amount of the variation in the composition of assemblages of benthic diatoms. At the national scale, a downstream ecological gradient was apparent, from fast-flowing, mostly oligotrophic highland streams to slow-flowing, mostly eutrophic lowland rivers. Our data suggest that spatial factors explain some of the variation in diatom distribution. The present investigation of the spatial patterns of benthic diatoms, the ecological determinants of diatom occurrence, and the identification of diatom indicator species contributes to development of a program for assessing the biological integrity of lotic ecosystems in Korea.

An algicidal bacterium Pseudomonas fluorescens HYK0210-SK09 (SK09) was applied to a natural bloom of Stephanodiscus hantzschii using a small-scale mesocosm (SM) and a large-scale mesocosm (LM) to clarify the algicidal effects and evaluate the response of the planktonic community and environments. When SK09 cells were inoculated at a final concentration of 5×10 6 cells mL −1 , the abundance of S. hantzschii decreased significantly by 95% in SM and 85% in LM. The microcosm in the laboratory revealed that the abundance of Pseudomonas increased rapidly after inoculation with a corresponding decrease in the S. hantzschii population. Nutrient concentrations increased following the decline in the diatom cells. The abundances of nondominant species such as Chlamydomonas, Cryptomonas, and Navicula increased slightly with increased nutrient concentrations. The abundance of heterotrophic protists also increased significantly due to utilization of SK09 as food. The present study demonstrates that SK09 is an effective biocontrol agent for natural S. hantzschii bloom, and grazing pressure plays a crucial role in the successful application of algicidal bacteria to natural environments.

Blooms of Alexandrium pacificum (formerly Alexandrium tamarense) are common in Chinhae Bay (Korea), presumably linked to anthropogenic eutrophication. Here we examine PSP toxin content and composition in axenic chemostat and batch cultures of A. pacificum using growth conditions that differed according to dilution rate, nutrient limitations, and enrichments. Phosphate (P)-limited cells in chemostat cultures had higher toxin content and a toxin composition that differed from that of nitrogen (N)-limited cells at the highest growth rates. Therefore, toxin composition changes do occur in axenic cultures of A. pacificum following extended growth under steady state conditions. In nutrient-limited batch cultures that received N and P enrichment, the N-enriched cultures showed a more diverse toxin profile than the P-enriched cells; the toxin content of N-enriched cells was lower than in the P-enriched cultures. We infer the following order for the biosynthesis of individual toxins: C1, C2>GTX3>GTX1>neoSTX.

Stable isotope tracers were first applied to evaluate the Microcystis cell assimilation efficiency of Sinanodonta bivalves, since the past identification method has been limited to tracking the changes of each chl-a, clearity, and nutrient. The toxicity profile and accumulation of MC-LR, -RR and -YR in different organs (foot and digestive organs) from the three filter-feeders (Sinanodonta woodiana, Sinanodonta arcaeformis, and Unio douglasiae) were assessed under the condition of toxigenic cyanobacteria (Microcystis aeruginosa) blooms through an in situ pond experiment using 13C and 15N dual isotope tracers. Chl-a concentration in the manipulated pond was dramatically decreased after the beginning of the second day, ranging from 217.5 to 15.6 μg·L−1. The highest amount of MCs was incorporated into muscle and gland tissues in U. douglasiae during the study period, at nearly 2 or 3 times higher than in S. woodiana and S. arcaeformis. In addition, the incorporated 13C and 15N atom % in the U. douglasiae bivalve showed lower values than in other bivalves. The results demonstrate that U. douglasiae has less capacity to assimilate toxic cyanobacteria derived from diet. However, the incorporated 13C and 15N atom % of S. arcaeformis showed a larger feeding capacity than U. douglasiae and S. woodiana. Our results therefore also indicate that S. arcaeformis can eliminate the toxin more rapidly than U. douglasiae, having a larger detoxification capacity.