Deleterious mutations destabilize ribosomal RNA in endosymbiotic bacteria

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 95; no. 8; pp. 4458 - 4462
• Main Authors: Lambert, J.D. (University of Arizona, Tucson, AZ.), Moran, N.A
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences of the United States of America 14.04.1998; National Acad Sciences; National Academy of Sciences; The National Academy of Sciences
• Subjects: Animals; Ants - microbiology; Aphids - microbiology; ARN RIBOSOMAL; ARN RIBOSOMIAL; BACTERIA; Bacteria - genetics; Bacterial Physiological Phenomena; Base Composition; Biological Evolution; Biological Sciences; BODY CONFORMATION; Coleoptera - microbiology; CONFORMACION ANIMAL; CONFORMATION ANIMALE; Diptera - microbiology; Ecological competition; Endosymbionts; Escherichia coli - genetics; Escherichia coli - physiology; ESTABILIDAD; Evolution; FILOGENIA; FREE LIVING BACTERIA; Genetic mutation; Genetic Variation; INSECTE NUISIBLE; INSECTOS DANINOS; MUTACION; MUTATION; Nucleic Acid Conformation; PEST INSECTS; PHYLOGENETICS; PHYLOGENIE; PHYLOGENY; Population size; Ribonucleic acid; RIBOSOMAL RNA; RICKETTSIALES; RNA; RNA, Ribosomal, 16S - chemistry; RNA, Ribosomal, 16S - genetics; SECONDARY STRUCTURE; Selection, Genetic; SIMBIONTES; STABILITE; STABILITY; SYMBIONTS; Symbiosis; SYMBIOTE; Taxa; WOLBACHIA PIPIENTIS
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.95.8.4458

In populations that are small and asexual, mutations with slight negative effects on fitness will drift to fixation more often than in large or sexual populations in which they will be eliminated by selection. If such mutations occur in substantial numbers, the combined effects of long-term asexuality and small population size may result in substantial accumulation of mildly deleterious substitutions. Prokaryotic endosymbionts of animals that are transmitted maternally for very long periods are effectively asexual and experience smaller effective population size than their free-living relatives. The contrast between such endosymbionts and related free-living bacteria allows us to test whether a population structure imposing frequent bottlenecks and asexuality does lead to an accumulation of slightly deleterious substitutions. Here we show that several independently derived insect endosymbionts, each with a long history of maternal transmission, have accumulated destabilizing base substitutions in the highly conserved 16S rRNA. Stabilities of Domain I of this subunit are 15-25% lower in endosymbionts than in closely related free-living bacteria. By mapping destabilizing substitutions onto a reconstructed phylogeny, we show that decreased ribosomal stability has evolved separately in each endosymbiont lineage. Our phylogenetic approach allows us to demonstrate statistical significance for this pattern: becoming endosymbiotic predictably results in decreased stability of rRNA secondary structure