Fig 1.
The upstream part of KAUST seawater reverse osmosis plant (A) and the schematic overview of the DNA recovery evaluation with different filtration volumes from tap (drinking) water in this study (B).
A 10% (v/v) solution of sodium metabisulfite (SMBS) (Na2S2O5) was used to quench the free chlorine (referred as dechlorination).
Fig 2.
Scheme of the batch experiments for evaluating DNA extraction yield via addition of E. coli cell solution.
The experiments were designed with three main scenarios: Tap water without E. coli spiking, tap water with E. coli spiking prior filtration, membrane spiking with E. coli without and after tap water filtration; and sub-scenarios (T: Tap water with residual chlorine, TD: Dechlorinated tap water, sterile: Tap water was pre-sterilized with membrane filtration to remove indigenous microbes, non-sterile: Tap water with no prior pre-filtration). Each replicate (n) comprises of four liters of tap water. Each treatment is explicitly assigned with the code shown at the second row of the table. Sterile mixed ester cellulose membrane filter (0.2 μm, 47 mm diameter) was used for tap water filtration (i.e., biomass collection). A 100 μL of 10% (v/v) solution sodium metabisulfite (SMBS) (Na2S2O5) was used as the dechlorinating agent.
Fig 3.
Cell concentration and DNA yield obtained from (T) tap water with residual chlorine and (TD) dechlorinated tap water.
The tap (drinking) water treatments were done by maintaining or removing residual chlorine, as summarized in Fig 2. A blue-coloured star indicates that total bacterial cell concentration was below the limit of detection (LOD) of flow cytometry which is 103 cells/mL. A red-coloured star indicates that the DNA concentration measured was below detection limit (BDL) of Qubit High Sensitivity assay dsDNA ≤ 0.01 ng/μL. The error bars show errors from three independent replicates.
Table 1.
DNA recovery from different filtration volumes of dechlorinated tap water before and after PCR, means ± SD.
Fig 4.
Total cell numbers and DNA yield obtained after Escherichia coli spiking into sterile and non-sterile (T) tap water with residual chlorine and (TD) dechlorinated tap water prior membrane filtration.
The details for (sterile, non-sterile) tap water treatments used for spiking treatments are summarized in Fig 2. Sterile: Tap water was pre-filtered by membrane filtration (0.2 μm, 47 mm diameter) before spiking. Non-sterile: Tap water without sterilization. + EC: Addition of Escherichia coli solution. A blue-coloured star indicates that total bacterial cell concentration was below the limit of detection (LOD) of flow cytometry which is 103 cells/mL. A red-coloured star indicates that the DNA concentration measured was below detection limit (BDL) of Qubit High Sensitivity assay dsDNA ≤ 0.01 ng/μL. The error bars show errors from triplicate samples.
Fig 5.
Total cells and DNA yield obtained from spiking onto membrane filters without and after tap water (T: Tap water with residual chlorine and TD: Dechlorinated tap water) filtration.
The details for membrane spiking treatments are summarized in Fig 2. T: Tap water containing residual chlorine. TD: Tap water with the removal of residual chlorine (addition of SMBS 10% (v/v)).–T + M + EC: Membrane spiked with E. coli only (without tap water filtration). +T + M + EC: Membrane spiked with E. coli after tap water (with residual chlorine) filtration. +TD + M + EC: Membrane spiked with E. coli after tap water (dechlorinated) filtration. The error bars show errors from triplicate samples.
Fig 6.
The extracted DNA concentration collected from dechlorinated tap water (A), membrane filters (B) spiked with Escherichia coli, and its subset (C) (sterile, non-sterile) dechlorinated tap water and membrane spiked with E. coli after filtration of dechlorinated tap water).
+ EC: Addition of Escherichia coli. TD: Dechlorinated tap water (addition of SMBS 10%). TD sterile: Dechlorinated tap water received prior membrane sterilization. TD non-sterile: Dechlorinated tap water without prior tap water sterilization.–T + M + EC: Membrane only (without tap water filtration) with the addition of E. coli. +T + M + EC: Membrane spiked with E. coli after filtration of tap water (residual chlorine). +TD + M + EC: Membrane spiked with E. coli after filtration of dechlorinated tap water. The error bars show errors from triplicate samples. P-value was shown for pairwise comparison (vs. control designees) based on ANOVA and post hoc Tukey’s test.