Degradation of organic pollutants by anaerobic methane-oxidizing microorganisms using methyl orange as example

Anaerobic oxidation of methane (AOM) microorganisms widespread in nature and they are able to utilize methane as electron donor to reduce sulfate, nitrate, nitrite, and high valence metals. However, whether persistent organic contaminants can also be degraded remains unknown. In this study, the organic pollutant methyl orange (MO) was used to address this open question. The initial concentration of MO affected its degradation efficiency and higher concentration (>100 mg/L) caused considerable inhibition. A ¹³CH₄ isotope experiment indicated that methane oxidation was involved in MO degradation, which produced N, N-dimethyl-p-phenylenediamine, and 4-aminobenzenesulfonic acid corresponded stoichiometrically. During the long-term experiment, the maximum degradation rate was 47.91 mg/(L·d). The percentage of Candidatus Methanoperedens and Pseudoxanthomonas significantly increased after 30-d of MO degradation under CH₄ conditions; moreover, Candidatus Methanoperedens dominated (46.83%) the microbial community. Candidatus Methanoperedens, either alone or in combination with Pseudoxanthomonas, utilized methane as the sole carbon source to degrade MO via direct interspecies electron transfer or the syntrophy pathway. This study will add to our understanding of the functions and applications of AOM microorganisms.