Katsura Sugiura

The use of an aquatic microcosm for pollution effects assessment

Abstract The effects of Cu 2+ ions and β-HCH (β-1,2,3,4,5,6-hexachlorocyclohexane) on microcosms containing bacteria, a protozoa ( Cyclidium ), two rotifers ( Philodina and Lepadella ) and a green alga ( Chlorella ) were investigated. The time-dependent changes in the respiration rate (community metabolic rate) were different from those of the control at a Cu 2+ ion concentration of 0.4 ppm and at a β-HCH concentration of 0.1 ppm. The calculation of the time-dependent changes in the respiration rate was assumed to be used as an index which determines whether the concentrations of the chemical agents have an effect on the material cycles in the system. This inference was supported by the results calculated using the mathematical model of changing the maximum (physiological) growth rate coefficient of organisms. In addition, the possibility of changes in the degree of changes in the respiration rate when changing the growth rate coefficient was discussed based on the kinds of constituent organisms and the structure of the system.

Microbial degradation of polychlorinated biphenyls in aquatic environments

Two bacterial strains belonging to the genus Pseudomonas were isolated from a lake sediment by using p-chlorobiphenyl as a sole carbon source. Metabolic degradation of various polychlorinated biphenyls (PCBs) was investigated. Some of PCBs were converted to chlorinated benzoic acids, and total mineralization was observed for monochlorinated and monobrominated biphenyls. Biodegradation kinetics was studied in shake cultures and in soil, both in the presence and absence of an alternative carbon source. The results showed that PCBs degrade better in the presence of another substrate, and that the solubility of PCBs in water and the desorption rate from soil plays a significant part in determining the degradation rate.

A mathematical model for microcosms: formation of the colonies and coupled oscillation in population densities of bacteria

A microcosm constructed, in the present study, consisted of bacteria (five or more species), green algae and rotifers and maintained a steady state for more than 100 days. This microcosm formed numerous colonies at the bottom of the flask and demonstrated coupled oscillation in the population densities of bacteria. The population dynamics and the spatial patterns of organisms were simulated using a cellular automata method. From the calculation results, the following facts were inferred: (1) heterogeneous metabolite concentrations due to the diffusion phenomenon as well as the frequencies of interactions among rotifers, bacteria and green algae and the strengths of their interactions are the contributing factors to the colony formation; (2) the system becomes stable when colonies are formed; and (3) coupled oscillation occurres in the population densities of bacteria when certain combinations are selected for the specific growth rate coefficients of the coexisting bacteria, and the distribution of the ratios of specific growth rate coefficients of the bacteria which can coexist in a stable manner is discrete rather than continuous.

The ABS (Autonomous Biological System): Spaceflight Results from a Bioregenerative Closed Life Support System

Materially-closed aquatic life support systems containing vascular plants, invertebrate animals, algae and microbes were tested in three space flight experiments with ground controls. Termed Autonomous Biological Systems (ABS), the 0.9 liter systems were completely isolated from spacecraft life support systems and cabin atmosphere contaminants, and needed minimal intervention from astronauts. The first experiment, aboard the Space Shuttle in 1996 for 10 days, was the first time that aquatic angiosperms were successfully grown in space. The second and third experiments aboard the Mir space station had 4-month durations, in 1996-97 and 1997-98, and were the first time that higher organisms (aquatic invertebrate animals) completed their life cycles in space. Compared to the ground control ABS, the flight units showed clearer water and slightly higher total organic carbon and soluble free amino acids. ABS units from all 3 flights returned as diverse and complex ecosystems. The ABS are the first completely bioregenerative, closed ecological life support systems to thrive in space, demonstrating their efficacy for research in space biology and gravitational ecology.

Effects of Al3+ ions and Cu2+ ions on microcosms with three different biological complexities

Cu(2+) ions or Al(3+) ions were added to microcosms containing three, four and eight species (S-3, S-4, S-8) at the beginning of the culture, or at the 15th day from the beginning of the culture to determine the production rates (P), the respiration rates (R), and P/R ratios. There was a balance between the oxygen production rates and the oxygen consumption rates in the microcosms (S-4) and (S-8), whereas there was no balance between two quantities in the microcosm (S-3). There were no significant differences in the Cu(2+) and Al(3+) ion concentrations influencing the material cycles and the metabolic balance between the case when the number of species was four and the case when the number of species was eight. It was assumed that the effects concentrations of the chemical substances are not significantly related to the degree of diversity of the constituent species in the microcosms having a balance between production and consumption.

Congener-specific PCB analyses of a sediment core of lake Shinji, Japan

Abstract Samples of a sediment core of Lake Shinji were analyzed for PCB congeners. KC-500 discharged from the nearby plant was assumed to be the sole cause of PCB contamination in this lake. The analytical results for biphenyls contanining four or more chlorine atoms indicated that the composition ratio was constant for the lower to upper layers of the sediment core sample. Correlations were found the PCB composition ratio of KC-500 to sediment and the values of Kow. The results suggested that PCBs are transported primarily in association with suspended sediment, and that the contribution of transfer based on diffusion of PCBs in the sediment is minimum in this lake.

Cultivation of bacterial with ecological capsules in space

Abstract A hermetically materially-closed aquatic microcosm containing bacteria, algae, and invertebrates was developed as a tool for determining the changes of ecological systems in space. The species composition was maintained for more than 365 days. The microcosm could be readily replicated. The results obtained from the simulation models indicated that there is a self-regulation homeostasis in coupling of production and consumption, which make the microcosm remarkably stable, and that the transfer of metabolites by diffusion is one of the important factors determining the behavior of the system. The microcosms were continuously irradiated using a 60 Co source. After 80 days, no elimination of organisms was found at any of the three irradiation levels (0.015, 0.55 and 3.0 mGy/day). The number of radio-resistance bacteria mutants was not increased in the microcosm at three irradiation levels. We proposed to research whether this microcosm is self-sustainable in space.