Electron acceptors modulate methane oxidation and active methanotrophic communities in anoxic urban wetland sediments
Ruiyu Yang, Chao Peng, Yongliang Mo, Sara Kleindienst, Shun Li, Jiajia Wang, Andreas Kappler, Zimeng Wang, Lu Lu
Abstract
ABSTRACT Urban wetlands, although often overlooked, are hotspots for CH 4 cycling. However, the understanding of anaerobic CH 4 oxidation and microbial responses to different electron acceptors in urban wetlands remains limited. Here, we employed DNA-stable isotope probing (SIP) and metagenomic techniques to identify the core CH 4 -oxidizing microbial groups in the presence of NO 3 - , SO 4 2- , or ferrihydrite (Fe(III)) in anoxic urban-lake sediments. The addition of NO 3 - to sediment microcosms promoted CH 4 oxidation, whereas SO 4 2- and Fe(III) had minimal or inhibitory effects on CH 4 oxidation rates in anoxic microcosms. The SIP-identified methanotrophs in response to the addition of CH 4 comprised the Marine Benthic Group D (MBG-D), “ Candidatus Methylomirabilis Sh765B-TzT-35 and Z114MB74,” and the putatively aerobic methanotrophs Methylobacter and Methylocystis . The presence of NO 3 - further enriched Methylocaldum , Methylomonas , ‘ Ca . Methylomirabilis Sh765B-TzT-35 and Z114MB74’, Methylococcaceae , and Methylospira . In contrast, SO 4 2- and Fe(III) amendments notably shifted the dominant methanotrophs through the significant labeling of Methylocystis . Furthermore, metagenomic analysis of 13 C-labeled DNA showed enrichment of genes for oxidation of CH 4 and its intermediates, as well as the reduction of NO 3 - , SO 4 2- , Fe(III), and fermentation. These results underscore the activity of NO 3 - -dependent CH 4 -oxidizing microorganisms and highlight their potential metabolic versatility in highly anthropogenically influenced urban wetlands. IMPORTANCE Urban wetlands are critical ecosystems for CH 4 cycling but are increasingly impacted by complex pollutants from urban development, such as nitrates, sulfates, and Fe(III) from industrial runoff, atmospheric deposition, and wastewater discharge. This study reveals how these pollutants act as electron acceptors, modulating microbial metabolic pathways and reshaping methanotrophic communities under anoxic conditions. By uncovering the microbial mechanisms driving CH₄ oxidation in urban wetland sediments, our findings provide a deeper understanding of how anthropogenic pollution alters biogeochemical cycles. These insights are crucial for developing targeted strategies to mitigate CH₄ emissions and improve greenhouse gas control in rapidly urbanizing regions.