ABSTRACT
Environmental DNA (eDNA) metabarcoding from water samples has, in recent years, shown great promise for biodiversity monitoring. However, universal primers targeting the cytochrome oxidase I (COI) marker gene popular in metazoan studies have displayed high levels of nontarget amplification. To date, enrichment methods bypassing amplification have not been able to match the detection levels of conventional metabarcoding. This study evaluated the use of universal metabarcoding primers as capture probes to either isolate target DNA or to remove nontarget DNA, prior to amplification, by using biotinylated versions of universal metazoan and bacterial barcoding primers, namely metazoan COI (mlCOIintF) and bacterial 16S (515F). Additionally, each step of the protocol was assessed by amplifying for both metazoan COI (mlCOIintF/jgHCO2198) and bacterial 16S (515F/806R) to investigate the effect on the metazoan and bacterial communities. Bacterial read abundance increased significantly in response to the captures (COI library), while the quality of the captured DNA was also improved. The metazoan-based probe captured bacterial DNA in a range that was also amplifiable with the 16S primers, demonstrating the ability of universal capture probes to isolate larger fragments of DNA from eDNA. Although the use of the tested COI probe cannot be recommended for metazoan enrichment, based on the experimental results, the concept of capturing longer fragments could be applied to metazoan metabarcoding. By using a truly conserved site without a high-level taxonomic resolution as a target for capture, it may be possible to isolate DNA fragments large enough to span over a nearby barcoding region (e.g., COI), which can then be processed through a conventional metabarcoding-by-amplification protocol.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
An error was located in the demultiplexing process of the manuscript methods, leading to a re-analysis of the results after correcting the bioinformatics pipeline. The results and discussion have been updated to reflect the newly analysed data. Additionally, the supplementary file ASV_table_with_tax.csv (ASV abundance table with taxonomy) was separated into two files, one for each COI and 16S libraries.