This paper describes interaction between sulfur-oxidizing bacteria and protozoa in a long time enrichment batch culture. The bacteria, collected from a neutralization plant of the abandoned Matsuo mine, has been cultured in an acidic environment (pH2), using iron-free 9K medium with elemental sulfur. In the culture, we have confirmed protozoa which belongs to Bodo edax, and whose sizes are about 5-15μm in length and 5-10μm in width. To investigate the interaction, time-dependency of the each number is examined under the following conditions: ventilation, air flow rate of 50, 25 cm3·s-1, shaking with a cycle of 2.2 s-1, and initial pH value, 1, 2, 3. The results obtained are summarized as follows:
(1) the ratio of protozoa to sulfur-oxidizing bacteria is nearly constant and from 10-1 to 10-4 in the enrichment culture;
(2) at initial pH value above 0.6, protozoa can increases, but decreases at the pH value less than 0.6;(3) when there exists protozoa in the enrichment culture, the yield factor of sulfur-oxidizing bacteria growth is about 1/7 of that in the protozoa-free case.
