The impact of electron acceptor variation and reactive oxygen species on microbial respiration rates

This thesis investigates how redox fluctuations in environments with chemical gradients, and the reactive oxygen species often produced by such fluctuations, affect microbial metabolism in permeable sediments in the German Wadden Sea and wastewater photogranules. Manuscript 1 finds that sulfate and nitrate reduction occur simultaneously, and that sulfate reduction rates are correlated with rates of dissimilatory nitrate reduction to ammonia in permeable sediments from the German Wadden Sea. Manuscript 2 finds that enzymatically removing reactive oxygen species from incubations of Wadden Sea sediments increases rates of sulfate and iron reduction and well as aerobic respiration. Furthermore, H2O2 was found in the upper sediments, controlling early diagenesis. Manuscript 2 also finds that while sulfate reduction does not occur simultaneously to oxygen consumption in permeable Wadden Sea sediments, it recovers instantly upon anoxia, meaning that the cells and their metabolic apparatus are not damaged by oxygen. Manuscript 3 finds that the removal of reactive oxygen species does not affect rates of denitrification or dissimilatory nitrate reduction to ammonia. It also finds that pretreatment of sediments with oxygen can increase sulfate reduction in the subsequent anoxic period. Furthermore, it finds that ROS can decrease sulfate reduction even in sediments that have not been recently exposed to oxygen. Manuscript 4 finds that wastewater photogranules are well adapted to extreme changes in nutrient and oxygen concentrations, performing carbon fixation over a large range of nutrient concentrations. It also finds evidence of aerobic denitrification.
Overall, this thesis finds that resident microbes are well adapted to environments with frequent redox changes, and exhibit “braided” use of electron acceptors. It nonetheless finds that the reactive oxygen species produced over oxic-anoxic transitions can substantially decrease microbial activity.