Enrichment of denitrifying methane-oxidizing microorganisms using up-flow continuous reactors and batch cultures

Area of Science:

• Microbiology
• Environmental Science
• Biogeochemistry

Background:

• Methane is a potent greenhouse gas, and its oxidation by microorganisms is crucial for mitigating climate change.
• Denitrifying anaerobic methane oxidation (DAMO) is a key process in environments like paddy fields, converting methane and nitrate/nitrite.
• Understanding DAMO microbial communities is essential for optimizing methane mitigation strategies.

Purpose of the Study:

• To enrich and characterize Denitrifying Anaerobic Methane Oxidizing (DAMO) microorganisms from paddy field soils.
• To investigate the influence of different electron acceptors (nitrate vs. nitrite) and cultivation methods (continuous-flow vs. batch) on DAMO microbial community structure and function.
• To determine the efficiency of methane oxidation and nitrite/nitrate reduction under various conditions.

Main Methods:

• Enrichment of DAMO microorganisms using continuous-flow and batch cultures with paddy field soil inocula.
• Cultivation with either nitrate or nitrite as the sole electron acceptor.
• Monitoring of methane oxidation and nitrite/nitrate reduction rates.
• Microbial community analysis using fluorescence in situ hybridization (FISH) and phylogenetic analysis of the pmoA gene.

Main Results:

• Continuous-flow cultures with nitrite demonstrated efficient simultaneous methane oxidation and nitrite reduction, enriching DAMO bacteria from the NC10 phylum.
• A maximum volumetric nitrite consumption rate of 70.4±3.4 mg-N·L(-1)·day(-1) was achieved with a short hydraulic retention time of 2.1 hours.
• Continuous-flow cultures with nitrite were dominated by bacteria (68%), with no archaea detected by FISH.
• Phylogenetic analysis revealed high sequence similarity (>98%) of enriched DAMO bacteria to the inoculum in continuous-flow cultures, contrasting with lower similarity (89-91%) in batch cultures.

Conclusions:

• The choice of electron acceptor and cultivation method significantly impacts the microbial community structure of DAMO consortia.
• Continuous-flow cultivation, particularly with nitrite, is effective for enriching specific DAMO bacteria (NC10 phylum) and achieving high methane oxidation rates.
• These findings provide insights into optimizing microbial processes for methane mitigation in anaerobic environments.