Polynucleobacter necessarius, a model for genome reduction in both free-living and symbiotic bacteria

Vittorio Boscaro, Michele Felletti, Claudia Vannini, Matthew S. Ackerman, Patrick S.G. Chain, Stephanie Malfatti, Lisa M. Vergez, Maria Shin, Thomas G. Doak, Michael Lynch, Giulio Petroni

Research output: Contribution to journalArticlepeer-review

59 Scopus citations


We present the complete genomic sequence of the essential symbiont Polynucleobacter necessarius ( Betaproteobacteria), which is a valuable case study for several reasons. First, it is hosted by a ciliated protist, Euplotes; bacterial symbionts of ciliates are still poorly known because of a lack of extensive molecular data. Second, the single species P. necessarius contains both symbiotic and free-living strains, allowing for a comparison between closely related organisms with different ecologies. Third, free-living P. necessarius strains are exceptional by themselves because of their small genome size, reduced metabolic flexibility, and high worldwide abundance in freshwater systems. We provide a comparative analysis of P. necessarius metabolism and explore the peculiar features of a genome reduction that occurred on an already streamlined genome. We compare this unusual system with current hypotheses for genome erosion in symbionts and free-living bacteria, propose modifications to the presently accepted model, and discuss the potential consequences of translesion DNA polymerase loss.

Original languageEnglish (US)
Pages (from-to)18590-18595
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number46
StatePublished - Nov 12 2013
Externally publishedYes


  • Burkholderiales
  • Genome streamlining
  • Nonsynonymous mutation rates
  • Protozoa
  • Symbiosis

ASJC Scopus subject areas

  • General


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