NC10 bacteria promoted methane oxidation coupled to chlorate reduction

The strictly anaerobic serum bottles were applied to investigate methane oxidation coupled to chlorate (ClO3−) reduction (MO-CR) without exogenous oxygen. 0.35 mM ClO3− was consumed within 20 days at the reduction rate of 17.50 μM/d, over three times than that of ClO4−. Chlorite (ClO2−) was not detected throughout the experiment and the mass recovery of Cl− was over 89%. Isotope tracing results showed most of 13CH4 was oxided to CO2, and the electrons recovery reached to 77.6%. Small amounts of 13CH4 was consumed for DOC production probably through aerobic methane oxidation process, with oxygen generated from disproportionation reaction. In pMMO (key enzyme in aerobic oxidation of methane) inhibition tests, ClO3− reduction rate was slowed to 7. 0 μmol/d by 2 mM C2H2, real-time quantitative PCR also showed the transcript abundance of pMMO and Cld were significantly dropped at the later period of experiment, indicating that the O2 disproportionated from ClO2− was utilized to active CH4. NC10 bacteria Candidatus Methylomirabilis, related closely to oxygenic denitrifiers M. oxyfera, was detected in the system, and got enriched along with chlorate reduction. Several pieces of evidence supported that NC10 bacteria promoted CH4 oxidation coupled to ClO3− reduction, these oxygenic denitrifiers may perform ClO2− disproportionation to produce O2, and then oxidized methane intracellularly.