‘Candidatus Methanoperedens’ is a genus of strictly anaerobic methanotrophic archaea (ANME). ANME mitigate the release of methane to the atmosphere by oxidizing this potent greenhouse gas to the less ...

Archaeal extrachromosomal elements (ECEs) are arguably the least well understood of all genetic elements, and few have >200 kbp (jumbo) genomes. Here, we report circular, jumbo ECEs with genomes of up to 535 kbp in length that associate with anaerobic methane-oxidizing Methanoperedens archaea. Notably, a 409-kbp genome related to jumbo ECEs is integrated into a subset of the ~4.2 Mbp Methanoperedens chromosomes at the tRNA-Asp genes. This represents the largest integrative element in Archaea and supports the jumbo ECE–host association. Multiple genome alignments and phylogenetic analyses suggest that the large ECE sizes developed by extensive DNA acquisition from Methanoperedens. The newly identified ECEs encode, and in some cases express, metabolic genes such as tetrahydromethanopterin S-methyltransferase exclusively involved in methane metabolism, and genes for nitrogen and sulfur compound transformations. Also encoded are defense systems, some of which are absent in hosts, such a

Archaeal extrachromosomal elements are poorly understood. Here, Shi et al. identify large, circular extrachromosomal elements associated with anaerobic methane-oxidizing archaea, encoding metabolic en...

Proceedings of the National Academy of Sciences (PNAS), a peer reviewed journal of the National Academy of Sciences (NAS) - an authoritative source of high-impact, original research that broadly spans...

U atmospheric scientists show proposed ‘geoengineering’ effort to remove potent greenhouse gas could worse air quality while providing minimal benefits

Consortia of anaerobic methane-oxidizing archaea and sulphate-reducing bacteria can grow with minimal amounts of free energy. Here, Guo et al. show that these consortia can oxidize carbon monoxide, wh...

In eutrophic coastal waters, aerobic methane-oxidizing bacteria (MOB) mitigate methane emissions by oxidizing benthic methane even in the stratified, anoxic water column. However, ongoing warming and eutrophication lead to extended stratification periods, enhancing anoxic and sulfidic conditions (euxinia), potentially affecting methane removal capacity. Here we compared overall water column methane removal between sites with irregular, seasonal and longer-term euxinia in the Stockholm Archipelago during summer 2022. The highest water–air methane emissions, bottom water–methane and sulfide accumulation, and the lowest methane oxidation potential were observed under longer-term euxinic bottom water conditions. While MOB relative abundance and potential activity indicated high functioning of the methane biofilter in the seasonally euxinic bottom water layer, the methane-filtering potential was much lower in the longer-term euxinic bottom water. Under persistent euxinic conditions, overall bacterial diversity and microbial network connectivity were lower, likely following a simultaneous shift in redox conditions and a shift toward anaerobic sulfur-cycling. This shift may force MOB to retreat from the euxinic bottom water into the narrow oxycline, reducing the capacity of the methane biofilter and resulting in higher methane emissions. These findings highlight the positive feedback loop that can further amplify oceanic methane emissions, particularly from eutrophic and shallow coastal waters prone to prolonged stratification under global warming.

Proceedings of the National Academy of Sciences (PNAS), a peer reviewed journal of the National Academy of Sciences (NAS) - an authoritative source of high-impact, original research that broadly spans...

Methane-munching symbionts fuel sea spiders in the deep sea