In order to evaluate Testacealobosia Arcella vulgaris as an indicator in nitrification process, the feeding habits on nitrifying bacteria and the effect of nitrogen compounds on the growth characteristics were examined comparing with those of Vorticella microstoma and Opercularia sp. In batch culture experiments, it was clear that A. vulgaris could grow well with Nitrosomonas europaea and Nitrobacter winogradskyi as food bacteria, whereas the growth of V. microstoma and Opercularia sp. was not observed. In addition, the inhibition effects of NH4-N and NO2-N on the growth of A. vulgaris were observed significantly. In continuous culture experiments, the strong relation between the concentration of A. vulgaris and nitrification ratio were found due to the close prey-predator relation with nitrifying bacteria and its high sensitivity to NH4-N concentration. It is suggested that A. vulgaris is a good indicator for nitrifying process.
