Unlinked rRNA genes are widespread among bacteria and archaea

• Published in: The ISME Journal Vol. 14; no. 2; pp. 597 - 608
• Main Authors: Brewer, Tess E., Albertsen, Mads, Edwards, Arwyn, Kirkegaard, Rasmus H., Rocha, Eduardo P. C., Fierer, Noah
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01-02-2020; Nature Publishing Group
• Subjects: 45/23; 631/158/855; 631/1647/514; 631/208/212/748; 631/326/171; Archaea; Archaea - genetics; Bacteria; Bacteria - genetics; Bacteriology; Biochemistry, Molecular Biology; Biodegradation; Biodiversity; Bioinformatics; Biomedical and Life Sciences; Computer Science; Ecology; Environmental Microbiology; Evolutionary Biology; Gastrointestinal Microbiome; Gene expression; Gene frequency; Gene regulation; Genes; Genes, rRNA; Genetics; Genomes; Genomics; Humans; Intracellular; Life history; Life Sciences; Metagenomics; Microbial Ecology; Microbial Genetics and Genomics; Microbiology; Microbiology and Parasitology; Natural environment; Phylogeny; Populations and Evolution; Quantitative Methods; Ribonucleic acid; Ribosomes; RNA; RNA, Ribosomal, 16S - genetics; RNA, Ribosomal, 23S; rRNA 16S; rRNA 23S; rRNA Operon - genetics
• ISSN: 1751-7362; 1751-7370
• DOI: 10.1038/s41396-019-0552-3

Ribosomes are essential to cellular life and the genes for their RNA components are the most conserved and transcribed genes in bacteria and archaea. Ribosomal RNA genes are typically organized into a single operon, an arrangement thought to facilitate gene regulation. In reality, some bacteria and archaea do not share this canonical rRNA arrangement—their 16S and 23S rRNA genes are separated across the genome and referred to as “unlinked”. This rearrangement has previously been treated as an anomaly or a byproduct of genome degradation in intracellular bacteria. Here, we leverage complete genome and long-read metagenomic data to show that unlinked 16S and 23S rRNA genes are more common than previously thought. Unlinked rRNA genes occur in many phyla, most significantly within Deinococcus-Thermus, Chloroflexi, and Planctomycetes, and occur in differential frequencies across natural environments. We found that up to 41% of rRNA genes in soil were unlinked, in contrast to the human gut, where all sequenced rRNA genes were linked. The frequency of unlinked rRNA genes may reflect meaningful life history traits, as they tend to be associated with a mix of slow-growing free-living species and intracellular species. We speculate that unlinked rRNA genes may confer selective advantages in some environments, though the specific nature of these advantages remains undetermined and worthy of further investigation. More generally, the prevalence of unlinked rRNA genes in poorly-studied taxa serves as a reminder that paradigms derived from model organisms do not necessarily extend to the broader diversity of bacteria and archaea.