Optimum growth condition and microcystin utilization in bacteria isolated from a lake and a rice field in Japan
2009
Satoh, M.(Tokai Univ., Shizuoka (Japan). School of Marine Science and Technology) | Ishii, H. | Abe, T.
Three Sphingomonas strains, S5, S6, and 7CY, capable of degrading hepatotoxin microcystins produced by a blue-green alga, were grown to evaluate the optimum growth condition in LB medium under various conditions as follows: temperature: 25, 30, 35, 40, 45 and 50degC; pH: 6.0, 7.0, 8.0, 9.0 and 10.0; and the density of ingredients of the medium: 1/4-fold, 1/2-fold and 1-fold. Under these conditions, S5, S6, and 7CY strains at 35degC showed the highest kg in 1/2-fold LB at pH 7.0, in l/2-fold LB at pH 8.0, and in LB at pH 7.0, respectively. Average generation times were 1.8 in S5, 1.7 in S6, and 2.4 hours in 7CY under each optimum condition. When microcystin-LR, -LY, -LW, and -LF were added to S6 cell suspension, S6 cells were able to degrade all these microcystins, and the rate of microcystin-LR degradation was 0.59 micro g/ml/day. S6 strains, furthermore, grew much faster in minimal medium in the presence of microcystin-LR than in the absence of the toxin. These results indicate that environmental factors such as pH and temperature which regulate the growth of microcystin-decomposing bacteria are considerably close to those of toxic blue-green algae. It is, therefore, suggested that water bodies where toxic blue-green algae are dominant should be convenient for these bacteria as well, and that they should take up microcystins as nutrient after toxic blue-green algae disappear. It should be noted that the rate of decomposing microcystins by S6 strain is high enough to exhaust microcystin-LR guideline value (1 micro g/l) recommended by WHO and the usual concentration of microcystins produced by blue-green algae in eutrophic water bodies.
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