No abstract

Environmental DNA (eDNA) metabarcoding is widely used for species analysis, while the use of environmental RNA (eRNA) metabarcoding is more limited. We conducted comparative eDNA/eRNA metabarcoding of the algae and arthropods (aquatic insects) in water samples from Naka River, Japan, to evaluate their potential for biological monitoring and water quality assessment. Both methods detected various algae and arthropod species; however, their compositions were remarkably different from those in traditional field surveys (TFSs), indicating low sensitivity. For algae, the species composition derived from eDNA and eRNA metabarcoding was equivalent. While TFSs focus on attached algae, metabarcoding analysis theoretically detects both planktonic and attached algae. A recently expanded genomic database for aquatic insects significantly contributed to the sensitivity and positive predictivity for arthropods. While the sensitivity of eRNA was lower than that of eDNA, the positive predictivity of eRNA was higher. The eRNA of terrestrial arthropods indicated extremely high or low read numbers when compared with eDNA, suggesting that eRNA could be an effective indicator of false positives. Arthropod and algae eDNA/eRNA metabarcoding analysis enabled water quality estimates from TFSs. The eRNA of algae and arthropods could thus be used to evaluate biodiversity and water quality and provide insights from ecological surveys.

Environmental nucleic acids (eDNA and eRNA) metabarcoding analyses have attracted considerable research attention as they non-invasively and cost-effectively monitor ecosystems. For heretofore unknown reasons, however, they often detect false positives. Here, we focused on domestic wastewater as a possible source of false positives and characterized fish nucleic acids in the influent and effluent of a wastewater treatment plant (WWTP). The metabarcoding analysis revealed that DNA and RNA detected in the influent wastewater originated from over 120 fish species, and most of these were consumed fish. The nucleic acid content was significantly higher in the influent than in the effluent, and the copy numbers of DNA in the influent were significantly higher than those of RNA. These findings were corroborated by the current literature and indicated that eRNA could effectively mitigate false positives. The present study demonstrated that rivers may be extensively contaminated by fish nucleic acids, and WWTPs substantially alter the quantities and ratios of fish DNA and RNA. Therefore, analyses of the wastewater near sampling points and coverage of the sewage system enable us to select and use the appropriate nucleic acid type (DNA or RNA) for metabarcoding analysis and improve the accuracy of fish species detection and identification.

Environmental DNA (eDNA) metabarcoding is widely used for species analysis, while the use of environmental RNA (eRNA) metabarcoding is more limited. We conducted comparative eDNA/eRNA metabarcoding of the algae and arthropods (aquatic insects) in water samples from Naka River, Japan to evaluate their potential for biological monitoring and water quality assessment. Both methods detected various algae and arthropod species, however, their compositions were remarkably different from those in traditional field surveys (TFSs), indicating a low sensitivity. For algae, the species composition derived from eDNA and eRNA metabarcoding was equivalent. While TFSs focus on attached algae, metabarcoding analysis theoretically detects both planktonic and attached algae. A recently expanded genomic database for aquatic insects significantly contributed to the sensitivity and positive predictivity for arthropods. While the sensitivity of eRNA was lower than that of eDNA, the positive predictivity of eRNA was higher. The eRNA of terrestrial arthropods indicated extremely high or low read numbers when compared with eDNA, suggesting that eRNA could be an effective indicator of false positives. Arthropod eDNA/eRNA metabarcoding analysis enabled water quality estimates from TFSs. The eRNA of algae and arthropods could thus be used to evaluate biodiversity and water quality and provide insights from ecological surveys.