Zen'ichiro Kawabata

Seasonal changes in densities of cyanophage infectious to Microcystis aeruginosa in a hypereutrophic pond

Seasonal changes in densities of cyanophages infectious to Microcystis aeruginosa were studied in a hypereutrophic pond from March 1997 to January 1998 to elucidate the potential impact of the cyanophage on M. aeruginosa mortality. Densities of M. aeruginosa ranged between 1.8 × 104 and 9.4 × 105 cells ml-1, while those of the cyanophages were between 2.0 × 102 and 4.2 × 104 PFU ml-1. Sharp decreases in densities of M. aeruginosa were detected on 10 June and 24 September, as densities of the cyanophages increased, suggesting release of the cyanophages due to the lysis of infected M. aeruginosa. Thus, infection by cyanophages may have a substantial effect on cyanobacterial succession in the pond. Densities of cyanophages became undetectable when those of M. aeruginosa were at low levels during winter. We suggest that there is a tight host-pathogen relationship between M. aeruginosa and the cyanophage in the pond.

Microbial interactions responsible for dissolved DNA production in a hypereutrophic pond

Concentration of dissolved DNA, microbial biomass, and consumption of bacteria by heterotrophic nanoflagellates (HNF) and ciliates were examined in a hypereutrophic pond for over 7 months to elucidate the main factors which influenced the release of dissolved DNA. Changes in concentration of dissolved DNA correlated well with both abundance of ciliates ( r = 0.788, p < 0.01) and rotifers ( r = 0.738, p < 0.01). A significant correlation was also found between dissolved DNA concentration and ciliate community ingestion rates ( r = 0.668, p <0.01). These results suggest that consumption of bacteria by ciliates is an important reason for the release of dissolved DNA.

Growth pattern and cellular nitrogen and phosphorus contents of the dinoflagellate Peridinium penardii (Lemm.) Lemm. causing a freshwater red tide in a reservoir

The population growth pattern and related changes in both the nitrogen and phosphorus contents in the cell of the dinoflagellate Peridinium penardii (Lemm.) Lemm., which formed a freshwater red tide in a reservoir, were studied in situ. An exponential increase with time in population density was found. A specific growth rate of 0.25 d−1 was observed. The cellular content of phosphorus per cell decreased from 6.0 × 10−5 µg to 9.2 × 10−6 µg along with an increase in population density from 8.0 × 102 cells ml−1 to 2.5 × 104 cells ml−1. A prominent change in the cellular nitrogen did not occur. Decreasing cell content and continuous uptake of phosphorus were advantageous for P. penardii to form a freshwater red tide under P-limited conditions.

Distribution pattern of the dinoflagellateCeratium hirundinella (O. F. Müller) Bergh in a reservoir

Horizontal distribution of the dinoflagellateCeratium hirundinella (O. F. Müller) Bergh in the Ishitegawa Reservoir, Ehime Prefecture, Japan, was investigated. Water quality was also surveyed. It was observed that the population ofC. hirundinella exponentially decreased in number from the head of the reservoir to the dam site. Further investigation proved thatC. hirundinella initiated growth at the head of the reservoir, and later gradually expanded downstream. It was found during the period of increase in water temperature that the cell density ofC. hirundinella at the uppermost station exponentially increased.

Dissolved DNA produced through a prey-predator relationship in a species-defined aquatic microcosm

Changes in concentration of dissolved DNA was studied in a species-defined microcosm consisting of bacteria Escherichia coli, protozoa Tetrahymena thermophila and algae Euglena gracilis. A marked increase in dissolved DNA was observed when T. thermophila grazed on E. coli and grew. This meant the prey–predatory relationship between E. coli and T. thermophila was responsible for the increase of dissolved DNA.

Effect of water temperature on the excystment of the dinoflagellate Ceratium hirundinella (O.F. Müller) Bergh

The effect of water temperature on the excystment of the dinoflagellate Ceratium hirundinella (O. F. Müller) Bergh was studied in the laboratory. Excystment was observed between 15–30 °C and was 2% at an optimum water temperature of 20 °C–25°C. Little excystment occurred between 5 and 10 °C. The results at low temperatures are not in accordance with those obtained in an English lake. This disagreement suggests an adaptability of excystment to the temperature regime of the lake.

Fate of a PCBS degrading recombinant pseudomonas putida AC30(PMFB2) and its effect on the densities of microbes in marine microcosms contaminated with PCBS

The fate of a genetically engineered microorganism, Pseudomonas putida AC30 (pMFB2) [AC30(pMFB2)], which is capable of degrading PCBs, and its effect on the densities of microbes were studied in seawater and seawater‐sediment microcosms contaminated with PCBs. In both microcosms AC30(pMFB2) had no apparent effect on the population densities of indigenous microbes such as virus, bacteria and phytoplankton. It was considered that this was caused by a rapid decrease of AC30(pMFB2). Obtained results confirmed that non‐indigenous genetically engineered microbes could not survive and had no significant effect on the population changes of indigenous microbes, as seen in other experiments.

Factors affecting the survival of genetically engineered Escherichia coli bearing a plasmid in a paddy field microcosm

In order to clarify some of the factors affecting the survival of a genetically engineered Escherichia coli (g‐E. coli) bearing a plasmid in a paddy field microcosm and its parent E. coli (p‐E. coli), we focused on protozoa and the metabolites of indigenous bacteria. It was found that both g‐E. coli and p‐E. coli decreased remarkably in a microcosm with protozoa but not so in that without protozoa. The populations of both g‐E. coli and p‐E. coli decreased much more in the metabolites of indigenous bacteria than in those of their respective metabolites. Therefore, the metabolites of indigenous bacteria as well as protozoa are factors affecting the decreases of both g‐E. coli and p‐E. coli in a paddy field microcosm.

Fate of a genetically engineered escherichia coli bearing a plasmid in a paddy field microcosm

Escherichia coli DH5 a pBluescript II SK+, bearing a plasmid which has a resistant gene to ampicillin as a genetically engineered bacteria (g‐E. coli) and its parent E. coli DH5 a (p‐E. coli), were introduced into a paddy field microcosm on the initial, 0.5th, 5th and 20th days after the microcosm was cultured. The population densities of both g‐E. coli and p‐E. coli decreased exponentially, irrespective of the day they were introduced. After that, p‐E. coli remained at 102 cells/ml level, but the population density of g‐E. coli was less than that of p‐E. coli and died out within 30 days. Neither g‐E. coli nor p‐E. coli had any effect on the population densities of indigenous bacteria and protozoa. From the point of population density, no interaction between g‐E. coli and p‐E. coli was found in the microcosm. Considering that there was no difference in the growth pattern between g‐E. coli and p‐E. coli in the single cultures in the microcosm medium, the indigenous community had the plasmid burden on the s...

Effect of ammonia on the survival of Zacco platypus (Temminck and Schlegel) at each developmental stage.

The survival rates were studied of fertilized eggs, larvae, fry, and adults of pale chub Zacco platypus (Temminck and Schlegel) exposed to various concentrations of ammonia. There was a decrease in hatching rate and an increase in deformed alevins at a concentration of 0.9 mg liter(-1) of ammonia. All alevins were deformed at a concentration of 1.6 mg liter(-1) of ammonia and no eggs hatched at a concentration of 3.1 mg liter(-1) of ammonia. No larvae survived for 84, 24 and 12 h at concentrations of 1.2, 2.0 and 4.7 mg liter(-1) of ammonia, respectively. Eighty percent of the fry died after 168 h and no fry survived for 24 h at concentrations of 1.6 and 2.1 mg liter(-1) of ammonia, respectively. Eighty percent of the adults died after 24 h and no adult survived for 12 h at concentrations of 1.0 and 1.9 mg liter(-1), respectively. Larger adults were the most susceptible to ammonia. The order of resistance to ammonia was eggs, fry, larvae, and adults.