Release and degradation of environmental DNA and RNA in a marine system

Abstract

Over the last decade, there has been growing interest in the analysis of environmental DNA (eDNA) to infer the presence of organisms in aquatic environments. The efficacy of eDNA/eRNA based tools are highly depend on the turnover rate of the molecule (their release and degradation). Environmental DNA has been shown to persist for days, weeks or years in environmental samples. Environmental RNA (eRNA) is thought to degrade faster than eDNA, however to our knowledge, no experimental studies have explored this. Here we present an aquarium study to investigate eDNA and eRNA shedding rates and degradation for two sessile marine invertebrates. The copy numbers for eDNA and eRNA we reassessed using droplet digital PCR targeting the mitochondrial Cytochrome c Oxidase subunit 1 (COI) gene. Environmental RNA persisted after organism removal for much longer than expected with detections for upto 13h. In contrast, eDNA was detected is samples collected upto 94h after organism removal. There was no evidence that the decay rates constants for eDNA and eRNA were different (p=0.6, Kruskal-Wallistests). Both eDNA and eRNA was detected in biofilms collected at the end of the experiment (day21). This suggests binding with organic or inorganic compounds or stabilization of these molecules in the biofilmmatrix. The finding of the prolonged persistence of eRNA may provide new opportunities for improved biodiversity surveys through reducing false positives caused by legacy DNA and could also facilitate new research on environmental transcriptomics.