BOLDigger – a Python package to identify and organise sequences with the Barcode of Life Data systems

Abstract

DNA metabarcoding workflows produce hundreds to ten-thousands of Operational Taxonomic Units (OTUs) or Exact Sequence Variants (ESVs) per analysis. In most workflows, a taxonomic assignment to these generated sequences is needed. This is typically done using publicly available databases. Especially, yet not exclusively, for Eumetazoan metabarcoding, the Barcode of Life Data system (BOLD) is the most comprehensive and curated reference barcode database and, therefore, typically the first choice for taxonomic assignment. While an application programme interface (API) exists to query data in large batches, no information on the many and important unpublished data are obtained through the API. The alternative approach using the BOLD identification engine on the website provides full access, yet it is restricted to 100 sequences at once. We developed a small platform-independent and graphical user interface (GUI) software package, BOLDigger, which aims to solve this problem by automating the process of sending successive requests of up to 100 sequences without surpassing the capacities of BOLD. BOLDigger can be used to download the results of the identification engine, as well as metadata for the obtained hits. For the selection of the best fitting hit, three different methods are implemented. A new approach, combining a threshold-based approach with the metadata information, was implemented to make use of the metadata.