Characterization of Simple Aquatic Microcosm for Ecotoxicity Screening

This study aimed at characterization of a simple aquatic microcosm consisting of algae Euglena gracilis as a producer, ciliate protozoa Tetrahymena thermophila as a consumer and bacteria Escherichia coli as a decomposer. The authors investigated changes in the cell densities, photosynthesis and respiration rates in the microcosm and its pure-culture systems when exposed or unexposed to copper. The following characteristics were deduced from the results. (1) The microcosm mimicked essential processes in natural aquatic microbial communities. That is, development of the microcosm could be regarded as a combination model of heterotrophic and autotrophic development in natural aquatic microbial communities. After such development, the microcosm reached a mature stage, in which the photosynthesis rate was balanced with the respiration rate. (2) The microcosm could evaluate not only direct effects of toxic agents but also community-level effects due to interspecies interactions or interactions between organisms and toxic agents. (3) The microcosm would have almost the same sensitivity to toxic agents as some other microcosms consisting of more diverse microbes. These three characteristics indicated that the microcosm studied was useful for community-level ecotoxicity screening for aquatic microbial communities.