Diat.barcode, an open-access barcode library for diatoms

Diatoms (Bacillariophyta) are ubiquitous microalgae which produce a siliceous exoskeleton and which make a major contribution to the productivity of oceans and freshwaters. They display a huge diversity, which makes them excellent ecological indicators of aquatic ecosystems, and can also be used to reconstruct paleoenvironments. Usually, diatoms are identified using characteristics of their exoskeleton morphology, which can be time consuming and error-prone. DNA-barcoding is an alternative to this and the use of High-Throughput-Sequencing enables the rapid analysis of many environmental samples at a lower cost than if specialist analysts are used. However, to identify environmental sequences correctly, an expertly curated reference library is needed. Several curated libraries for protists exists; none, however, are dedicated to diatoms. Diat.barcode is an open-access library dedicated to diatoms which has been maintained since 2012. It was initiated with the barcoding network of INRA (French National Institute for Agricultural Research) R-Syst, is now an international initiative partly supported by a Cost network (DNAqua-net). Data come from two sources (1) the NCBI nucleotide database (National Center for Biotechnology Information) and (2) unpublished sequencing data of culture collections in France, UK and Russia. Since 2017, several European experts have collaborated to curate this library for rbcL, a chloroplast marker suitable for species-level identification of diatoms. For the latests versions of the database, more than 7800 curated barcodes are available. The database is accessible through https://www6.inra.fr/carrtel-collection_eng/Barcoding-database. A ready-to-use subset of the database for metabarcoding analyses is also accessible.