Abstract
The crustacean zooplankton Daphnia magna is highly sensitive to chemicals and it has been used for chemical toxicity tests according to the OECD guidelines. Recently we identified symbiotic bacteria in Daphnia magna, which plays critical roles on the growth and the reproduction. To evaluate the effects of symbiotic bacteria on the chemical sensitivity of Daphnia, bacteria-free Daphnia were prepared and chemical sensitivities were compared between bacteria-free Daphnia and normal Daphnia (with symbiotic bacteria) under the acute immobilization test.
Firstly we developed a method for preparation of bacteria-free Daphnia. The elimination of symbiotic bacteria was confirmed by PCR targeted to bacterial 16S ribosomal DNA. Then acute immobilization test was performed using the bacteria-free Daphnia. Normal Daphnia showed greater chemical resistance to higher concentration of Nonylphenol, Fenoxycarb and Pentachlorophenol than bacteria-free Daphnia. Interestingly, toxicity of antimicirobial reagent Triclosan did not show significant difference between normal and bacteria-free Daphnia.
These results suggested potential roles of symbiotic bacteria in relation to the chemical resistance of its host Daphnia. Thus it is possible that multiple contaminant including antibiotics may rise the sensitivity of Daphnia to chemicals and that the differences of toxicity data on Daphnia among laboratories may partly depend on the composition of symbiotic bacteria.
