London Calling 2023: Confirmation of Borg extrachromosomal genomes: analysis of their methylation patterns, metabolism, and tandem repeats

Huge novel extrachromosomal elements termed Borgs were recently associated with anaerobic methane-oxidizing archaea of the genus "Candidatus Methanoperedens". Oxford Nanopore assemblies yielded large fragments of previously partially sampled genomes and brought to light nine new Borg genomes, two of which were fully curated into the terminal inverted repeat regions. Nanopore sequencing reads also enabled identification of the native methylation patterns of Borg genomes and their hosts. An essentially complete, circularized nanopore-based 4.0 Mbp Methanoperedens genome was also recovered, polished to completion using Illumina reads, and used to compare its metabolic capacities with those provided by the associated Borgs. Overall, the findings confirm all key features of Borg genomes and substantially expand the genomic sampling of these enigmatic extrachromosomal elements of methane-oxidizing archaea.