A novel method to isolate free-floating extracellular DNA from wastewater for quantitation and metagenomic profiling of mobile genetic elements and antibiotic resistance genes
Antibiotic resistant genes (ARGs) and mobile genetic elements (MGEs) can be found in the free-floating extracellular DNA (eDNA) fraction of microbial systems. These xenogenic components can generate bacterial cells resistant to one or more antibiotics by natural transformation. Because of low concentration in wastewater, the obtaining of a high quality and a high yield of eDNA extract is challenging. We developed a method using chromatography to isolate eDNA without causing cell lysis (often unchecked) from complex wastewater matrices. The chromatographic step involved a diethylaminoethyl-cellulose-monolithic column to capture the eDNA found in cell-free filtered wastewater samples (e.g. influent wastewater, activated sludge and treated effluent wastewaster). Free-floating eDNA yields from 1 L of influent, activated sludge and treated effluent water reached 12.5 ± 1.9 µg, 12.3 ± 1 µg and 5.6 ± 2.9 µg of raw eDNA and 9.0 ± 0.7 µg, 5.6 ± 0.46 µg and 2.6 ± 1.3 µg of purified eDNA, respectively. In order to check the suitability of free-floating eDNA extracts for molecular analysis, qPCR and metagenomics were performed. eDNA extracts from treated effluent water were analyzed by qPCR to quantify a selected panel of ARGs and MGEs. Microbiome, resistome, and mobilome profiles from activated sludge free-floating eDNA were measured by metagenomic sequencing. Between iDNA and eDNA fractions, qPCR showed differences of 0.94, 1.11, 1.92 and 1.32 log10 gene copies mL-1 for sulfonamides resistant genes (sul1 and sul2), beta-lactamase resistance gene blaCTXM, and the class 1 integron-integrase (intI1) MGE, respectively. These differences highlighted the crucial need for an isolation method to discern both iDNA and eDNA to understand ARGs persistence and quantity in complex cultures. The eDNA yields obtained from 1 L of activated sludge (3.6 g of total suspended solids L-1) samples were substantially higher than the amount of DNA template needed for high-throughput sequencing (>1 µg) in service facilities. Subsystems classification showed that the eDNA metagenome was mainly composed by MGEs (65.1%). The 35.9% rest related to traditional functional genetic signatures. It was the first time the resistome from the eDNA fraction was analyzed showing lower number of primary aligned reads when compared to the iDNA and a predominance of aminoglycosides and β-lactamams. Metagenome results showed that eDNA can not be discarded as a pool of ARGs and MGEs for horizontal gene transfer. This novel isolation method was powerful to elucidate the molecular compositions of free-floating eDNA fractions in complex environmental samples such as wastewater environments at different microbial densities. Data obtained using this extraction method will foster xenogenic and microbial risk assessments across urban and natural water systems. This will support water authorities in the delineation of measures to adopt at wastewater treatment plants to remove them and safeguard environmental and public health. ### Competing Interest Statement The authors have declared no competing interest.
- Downloaded 434 times
- Download rankings, all-time:
- Site-wide: 44,587 out of 105,623
- In molecular biology: 1,458 out of 3,584
- Year to date:
- Site-wide: 10,614 out of 105,623
- Since beginning of last month:
- Site-wide: 7,381 out of 105,623
Downloads over time
Distribution of downloads per paper, site-wide
- 18 Dec 2019: We're pleased to announce PanLingua, a new tool that enables you to search for machine-translated bioRxiv preprints using more than 100 different languages.
- 21 May 2019: PLOS Biology has published a community page about Rxivist.org and its design.
- 10 May 2019: The paper analyzing the Rxivist dataset has been published at eLife.
- 1 Mar 2019: We now have summary statistics about bioRxiv downloads and submissions.
- 8 Feb 2019: Data from Altmetric is now available on the Rxivist details page for every preprint. Look for the "donut" under the download metrics.
- 30 Jan 2019: preLights has featured the Rxivist preprint and written about our findings.
- 22 Jan 2019: Nature just published an article about Rxivist and our data.
- 13 Jan 2019: The Rxivist preprint is live!