Optimization of environmental DNA-based methods: A case study for
detecting brook trout (Salvelinus fontinalis).
Abstract
The utility of eDNA for fish species and community monitoring is
well-established using targeted amplification (i.e., qPCR and ddPCR) and
passive sequencing approaches (i.e., metabarcoding). However, the lack
of optimized and standardized methods reduces the sensitivity of this
approach and precludes the reliable comparison of findings across
studies, respectively. DNA extraction is a prime target for optimization
efforts because the extraction method is highly variable across eDNA
studies despite being the most influential factor in detection
efficiency across the entire post-collection workflow. Sequence analysis
is arguably the least standardized step in the workflow, with new
bioinformatics pipelines frequently emerging in the literature and being
implemented with innumerable unique combinations of parameter values.
The current study aimed to support the optimization and standardization
of eDNA methods for fish detection by assessing two commercial DNA
extraction kits manufactured by Qiagen and Macherey-Nagel on cost, time,
and performance specifications and comparing the success of brook trout
detection by metabarcoding across three bioinformatics pipelines, qPCR,
and ddPCR. Our protocols were effective in detecting brook trout in all
20 samples analyzed. Brook trout eDNA was detected by ddPCR in nine
(90%) Qiagen extracts but only seven (70%) Macherey-Nagel extracts. In
comparison, detection success was equal across the two extraction kits
using qPCR (70%) and metabarcoding (100%). The metabarcoding pipelines
performed equally well in detecting brook trout with no significant
differences in read numbers associated with the target species. Under
our experimental conditions, the Qiagen kit was selected as the
preferred kit due to its overall good performance and considerably lower
cost despite a slightly longer extraction time.