A key limitation in our understanding of microbial ecology and evolution is the fact that a large proportion of microorganisms remains unculturable. One method used to bypass this bottleneck is metagenomics — shotgun sequencing of DNA directly extracted from environmental samples — followed by genome assembly. However, even this technique is not fully effective for genome sequencing of rare species owing to the difficulties in binning (classification of reads into taxons) and in the assembly of individual genomes from complex metagenomes. The authors of this study developed a new differential coverage binning approach for the assembly of high-quality genomes from rare species. By testing it on DNA from an activated sludge bioreactor, they were able to assemble 12 complete or near-complete genomes, four of which belonged to the candidate phylum TM7, which the authors rename Saccharibacteria.