this study expand the understanding of redox fluctuations in association with the degradation of recalcitrant substrates in soil and the corresponding microbiome.. Reduction–Oxidation Fluctuations Shape the Soil Microbiome in the Hypoxic Bioremediation of Octachlorinated Dibenzodioxin- and Dibenzofuran-Contaminated Soil

The biodegradation of polychlorinated-p-dioxins and dibenzofurans (PCDD/Fs) has been recently demonstrated in a single reactor under hypoxic conditions. Maintaining hypoxic conditions through periodic aerations results in a marked fluctuation of reduction–oxidation (redox) potential. To further assess the effects of redox fluctuations, we operated two fed-batch continuously stirred tank reactors (CSTRs) with sophisticated redox controls at different anoxic/oxic fluctuations to reduce PCDD/Fs in contaminated soil. The results of long-term reactor operation showed that the CSTR with redox fluctuations at a narrow range (−111±56 mV) (CSTR_A) revealed a higher substrate hydrolysis activity level and PCDD/F degradation rate than did the CSTR with a redox potential that fluctuated at a broad range (1±114 mV) (CSTR_B). In accordance with analyses of bacterial 16S rRNA genes, the designated hypoxic conditions with added compost supported survival of bacterial populations at a density of approximately 109 cells/g slurry for both reactors. The evolved core microbiome was dominated by anoxic/oxic fluctuation-adapted Bacteroidetes, Alphaproteobacteria, and Actinobacteria, with higher diversity and complexity in addition to more abundant functionality of hydrolysis, including hydrolytic dehalogenases, and a higher degradation of dioxin-like compounds in CSTR_A than in CSTR_B. Taken together, the overall results of this study expand the understanding of redox fluctuations in association with the degradation of recalcitrant substrates in soil and the corresponding microbiome