An activated sludge sample that had originally been collected from an aeration tank of the Stickney wastewater treatment plant in Chicago, and... Show moreAn activated sludge sample that had originally been collected from an aeration tank of the Stickney wastewater treatment plant in Chicago, and had previously been cultured at low dissolved oxygen (DO) for 48 weekly passages was used as starting material for continuation of the low DO acclimation. The culture was continued at low dissolved oxygen in synthetic wastewater for 25 additional weekly passages to study what would happen to the activated sludge if the low DO continued. In order to do that, some important data were measured during the culture, including the specific oxygen uptake rates (SOUR) which could reflect the ability of oxygen utilization, 16S rDNA information which could tell the community diversity of sludge, and the dominant species genome data which suggested what really happened to the sludge and some reasons. The results showed that SOUR decreased modestly during the course of low DO adaptation, which was contrary to the results of the previous study. There were significant changes in community structure with respect to bacterial species during the first fifteen additional passages. Species known to produce both flavohemoglobins (FHbs) and truncated hemoglobins (trHbs) were common at all passages tested, although the dominant species were totally different from passage to passage. Specifically, during the course of the experiment, the frequency of cells encoding an FHb decreased substantially, from 84% to 50%, while the percentage of cells encoding a trHb decreased slightly from 84% to 78%. The overall content in the culture of heme b (the heme type found in bacterial hemoglobins) decreased, however, during continuation of the low DO conditions. So it is indicated that the oxygen utilization ability of the activated sludge does not increase all the time. M.S. in Biology, May 2016 Show less
