About PR2

The eukaryotic tree. From Burki et al. 2019. The New Tree of Eukaryotes. Trends in Ecology & Evolution. DOI: 10.1016/j.tree.2019.08.008.

Current version : 4.14.0
Last update : 25 June 2021

The PR2 sequence database

The PR2 sequence database was initiated in 2010 in the frame of the BioMarks project from work that had developed in the previous ten years in the Plankton Group of the Station Biologique of Roscoff. Its aim is to provide a reference database of carefully annotated 18S rRNA sequences using eight unique taxonomic fields (from kingdom to species). At present it contains about 184,000 sequences. A number of metadata fields are available for many sequences, including geo-localisation, whether it originates from a culture or a natural sample, host type etc… The annotation of PR2 is performed by experts from each taxonomic groups. One very important project in this respect is EukRef which has recently decided to merge its effort with PR2. EukRef has built bioinformatics pipelines that have been used during three workshops dedicated to specific taxonomic groups. As an example, part of the ciliate annotation originate from the first EukRef workshop.

Representation of the different taxonomic groups within PR2.

The PR2 primer database

We have developed in 2020 an interactive pr2-primers database focusing on the rRNA operon. You can download primer and primer sets. Primer pairs are evaluated against the PR2 sequence database and you can test your own primers.


Guillou, L., Bachar, D., Audic, S., Bass, D., Berney, C., Bittner, L., Boutte, C. et al. 2013. The Protist Ribosomal Reference database (PR2): a catalog of unicellular eukaryote Small Sub-Unit rRNA sequences with curated taxonomy. Nucleic Acids Res. 41:D597–604.

del Campo J., Kolisko M., Boscaro V., Santoferrara LF., Nenarokov S., Massana R., Guillou L., Simpson A., Berney C., de Vargas C., Brown MW., Keeling PJ., Wegener Parfrey L. 2018. EukRef: Phylogenetic curation of ribosomal RNA to enhance understanding of eukaryotic diversity and distribution. PLOS Biology 16:e2005849. DOI: 10.1371/journal.pbio.2005849.

Vaulot, D., Mahé, F., Bass, D., & Geisen, S. (2021). ╔pr2-primer : An 18S rRNA primer database for protists. Molecular Ecology Resources, in press. DOI: 10.11111755-0998.13465


Report on GitHub

Get the PR2 databases


You can contribute to the PR2 database in different ways.

  • The EukRef project has developed pipelines to obtain sequences from a given phylogenetic group. It organizes workshops focused on specific groups (more information soon on up-coming workshops).
  • You can also provide expert annotation or metadata for a taxonomic group you have analyzed in the framework of your thesis or a specific project. See detailed instructions here.

The PR2 Team

Core team


Javier del Campo

U. Miami, USA

Microbial Ecology and Evolution


Frédéric Mahé

CIRAD, France



Daniel Vaulot

NTU, Singapore

Marine Phytoplankton


Laure Guillou

CNRS, France

Marine parasites

Scientific Committee


Fabien Burki

Uppsala U., Sweden

Tree of eukaryotes, phylogenomics, metabarcoding, long-reads, protists, diversity


Bente Edvardsen

U. Oslo, Norway



Martin Kolísko

CAS, Czech Republic



Ramon Massana

ICM, Spain



Fabrice Not

CNRS, France



Laura Parfrey

UBC, Canada



Luciana Santoferrara

Hofstra University, USA