Techniques &applications: A first genome assembly for nanopore sequencing

Metagenomic surveys have identified uncultivated microbial species whose genomes are predicted to correspond to ultra-small cell sizes. In a new study, Brown et al. describe the genomes of 797 ultra-small bacteria obtained by metagenomic sequencing of 0.2 μm filtrates from aquifier samples. The genomes coalesced into ~35 candidate phyla, which the authors propose represent a ‘candidate phyla radiation (CPR)’ of common origin that may comprise more than 15% of the bacterial domain. CPR genomes have several unusual features, including in ribosomal genes: all genomes lack the gene for ribosome protein L30 (rpL30); one-third of the genomes have a self-splicing intron and/or open reading frame insertion in the 16S rRNA gene; and some of the genomes do not encode rpL1 or rpL9, which were thought to be universal in bacteria.