Abstract Anaerobic Oxidation Of Methane Research Articles

Active pathways of anaerobic methane oxidization in deep-sea cold seeps of the South China Sea.

Anaerobic oxidation of methane (AOM) is critical for controlling methane emissions from deep-sea cold seeps. Microbial groups associated with different AOM processes have been briefly investigated, but the AOM activities associated with the utilization of different electron acceptors in the deep-sea methane seeps remain largely unknown. Here, surface sediments (0-4 cm) from two cold seeps (Site F/Haima) and the Xisha trough in the South China Sea (SCS) were incubated to measure AOM potentials driven by nitrite, nitrate, and sulfate as different electron acceptors with isotopically labeled methane gas (13CH4), and the population shifts of microbial communities along the incubation were investigated by high-throughput sequencing and quantitative polymerase chain reaction based on both the 16S rRNA gene and functional genes. Nitrite and nitrate were preferentially used prior to sulfate during the incubation, and nitrate-/nitrite-dependent anaerobic methane oxidation (Nr-/N-DAMO) contributed more to the methane flux in both the cold seeps and the trough. The highest rates of DAMO and sulfate-dependent anaerobic methane oxidation (SAMO) were detected at Site F, consistent with the transcript abundance of mcrA and dsrB genes during the incubation, and might be explained by the in situ active functional groups. The former process might be explained by Campylobacteria, which could couple sulfide oxidation and nitrate consumption to further participate in the N-DAMO process, while the latter process might be due to the higher proportions of Desulfobacterota. This study elucidates the diversity and potential activities of major microbial groups in the DAMO and SAMO processes in the deep-sea cold seeps using isotopic tracing incubations and provides direct evidence for the occurrence of Nr-/N-DAMO as a previously overlooked microbial methane sink in the deep-sea hydrate-bearing sediments in the SCS. IMPORTANCE Cold seeps occur in continental margins worldwide and are deep-sea oases. Anaerobic oxidation of methane is an important microbial process in the cold seeps and plays an important role in regulating methane content. This study elucidates the diversity and potential activities of major microbial groups in dependent anaerobic methane oxidation and sulfate-dependent anaerobic methane oxidation processes and provides direct evidence for the occurrence of nitrate-/nitrite-dependent anaerobic methane oxidation (Nr-/N-DAMO) as a previously overlooked microbial methane sink in the hydrate-bearing sediments of the South China Sea. This study provides direct evidence for occurrence of Nr-/N-DAMO as an important methane sink in the deep-sea cold seeps.

Anaerobic Oxidation of Methane in Sediments of Lake Constance, an Oligotrophic Freshwater Lake

Anaerobic oxidation of methane (AOM) with sulfate as terminal electron acceptor has been reported for various environments, including freshwater habitats, and also, nitrate and nitrite were recently shown to act as electron acceptors for methane oxidation in eutrophic freshwater habitats. Radiotracer experiments with sediment material of Lake Constance, an oligotrophic freshwater lake, were performed to follow 14CO2 formation from 14CH4 in sediment incubations in the presence of different electron acceptors, namely, nitrate, nitrite, sulfate, or oxygen. Whereas 14CO2 formation without and with sulfate addition was negligible, addition of nitrate increased 14CO2 formation significantly, suggesting that AOM could be coupled to denitrification. Nonetheless, denitrification-dependent AOM rates remained at least 1 order of magnitude lower than rates of aerobic methane oxidation. Using molecular techniques, putative denitrifying methanotrophs belonging to the NC10 phylum were detected on the basis of the pmoA and 16S rRNA gene sequences. These findings show that sulfate-dependent AOM was insignificant in Lake constant sediments. However, AOM can also be coupled to denitrification in this oligotrophic freshwater habitat, providing first indications that this might be a widespread process that plays an important role in mitigating methane emissions.