Transport Of Bacteriophages Research Articles

F-Specific RNA Bacteriophage Transport in Stream Water: Hydro-Meteorological Controls and Association with Suspended Solids

F-specific RNA bacteriophages (FRNAPHs) are commonly used as indicators of faecal and viral contamination in waters. Once they enter surface waters, the exact role of suspended solids, sediments and hydro-meteorological factors in their fluvial fate and transport is poorly understood, and long-term studies (e.g., over years) are lacking. In this study, FRNAPH concentrations and genogroup distribution were measured in the Orne River (France) during two years at weekly intervals, and during four storm runoff events. Hydro-meteorological driving factors were investigated at both time scales. FRNAPH concentrations and genogroups at different depths of a riverbank sediment core were also examined to better discriminate the origin of the faecal pollution. During low flows, the FRNAPH and the suspended solid transport were decoupled and the FRNAPH concentrations were mainly correlated with the air and water temperature. During storm runoff events, the FRNAPH concentrations only showed a significant correlation with conductivity, turbidity and water discharge. Despite the uncertainty of the predictions, multi parameter regression models using hydro-meteorological variables were suitable to predict log transformed FRNAPHs’ concentrations at low flows with a standard error of 0.46. Model performance using the storm runoff events dataset was low. This study highlights different driving factors at low flows and during storm runoff events, and the need to measure at both time scales to better understand phage transport dynamics in surface water.

Evaluating Bacteriophage P22 as a Tracer in a Complex Surface Water System: The Grand River, Michigan

Viruses are important pathogens in both marine and fresh water environments. There is a strong interest in using bacteriophages as tracers because of their role as model viruses, since dissolved chemical tracers may not adequately describe the behavior of viruses that are suspended colloids. Despite a large number of studies that examined the transport of bacteriophages in the subsurface environment, few studies examined phage transport in large and complex surface water systems. In this paper we report the results of a dual tracer study on a 40 km reach of the Grand River, the longest river in Michigan, and we examine the performance of bacteriophage P22 relative to a chemical tracer (Rhodamine WT). Our analysis based on the transient storage (TS) model indicated that P22 can be successfully used as a tracer in complex surface water environments. Estimated P22 inactivation rates were found to be in the range 0.27-0.57 per day (0.12-0.25 log10 per day). The highest inactivation rate was found in a reach with high suspended solids concentration, relatively low dissolved organic carbon content, and sediment with high clay content. Estimated TS model parameters for both tracers were found to be consistent with surficial geology and land use patterns. Maximum storage zone sizes for the two tracers were found in different river reaches, indicating that different processes contributed to TS within the same reach for the two tracers. This model can be used to examine the arrival times and concentrations of human viral pathogens released from untreated sewage at recreational areas.

Influence of DOC on MS-2 Bacteriophage Transport in a Sandy Soil

The purpose of this study was to investigate the influence of dissolved organic carbon (DOC) on MS-2 bacteriophage transport in a sandy soil. Miscible-displacement experiments were conducted to examine the retention and transport of MS-2, at two influent concentrations, in the absence and presence of DOC. Effluent recoveries of MS-2 were similar for both sets of experiments. The results of the experiments were analyzed with a mathematical model that incorporated inactivation and rate-limited attachment/detachment. The optimized attachment rate coefficients were similar for all experiments. These results indicate that DOC had no significant influence on the transport of MS-2 in this soil. A mass-balance analysis based on the mathematical-modeling results revealed that attachment was significant during the early stages of the experiments, and that the majority of attached MS-2 became inactivated by the time the experiments were completed.

Fate and transport of bacteriophage in UK aquifers as surrogates for pathogenic viruses

Recent threats to groundwater quality in the UK (arising from leaking sewers and burial pits used during the recent Foot and Mouth Disease epidemic) have highlighted the need to understand the fate and transport of pathogenic viruses in the subsurface so that a robust assessment of their potential threat to environmental and public health can be made. Non-hazardous microbial tracers (phage) that mimic the movement of pathogenic microorganisms through groundwater systems are being used. Bacteriophage have good potential as surrogates to help us better understand the fate and transport of viral pathogens and are discussed here in the light of their injection as tracers into UK aquifers. Specific bacteriophages (MS2, PRD1 and ϕX174) that exhibit good potential as tracers and have properties similar to pathogenic viruses of interest are discussed.

Virus Transport Experiments in a Sandy Aquifer

The occurrence of human enteric viruses in ground water has been well documented in the literature. Bacteriophages such as MS-2 and PRD1 have properties similar to pathogenic human viruses suggesting that bacteriophages can be used as proxies for virus transport. The objective of this study is to investigate a “worst case scenario” for virus transport in a ground water aquifer, i.e., sand and gravel aquifer under a forced-gradient, by using bacteriophages. Field studies have been conducted to trace large-scale (34 m) and small-scale (10 m) virus transport under natural- and forced-gradients through a sand and gravel aquifer at a ground water research site at the Texas A&M University. Virus transport was monitored under natural and forced-gradient conditions using MS-2 and PRD-1 as virus tracers and bromide as a conservative tracer. Results indicate virus and bromide transport to down-gradient monitoring wells in both the large- and small-scale field tests. During the tests conducted, MS-2 transport appears to exhibit little longitudinal dispersion, showing a narrow peak at the well nest 34 m down-gradient in 13 days which is 20 days before the bromide breakthroughs, indicating that bacteriophage transport through the aquifer was mainly by advective flow. Differences in tracer transport can be attributed to the heterogeneity of the sand and gravel aquifer at the site, different injection methods, different sampling methods, and different tracer properties. Heterogeneity of the aquifer would cause virus transport through preferential flow paths.

Bacteriophage transport through a fining-upwards sedimentary sequence: laboratory experiments and simulation

A column containing four concentric layers of progressively finer-grained glass beads (graded column) was used to study the transport of the bacteriophage T7 in water flowing parallel to layering through a fining-upwards (FU) sedimentary structure. By passing a pulse of T7, and a conservative solute tracer upwards through a column packed with a single bead size (uniform column), the capacity of each bead type to attenuate the bacteriophage was determined. Solute and bacteriophage responses were modelled using an analytical solution to the advection–dispersion equation, with first-order kinetic deposition simulating bacteriophage attenuation. Resulting deposition constants for different flow velocities indicated that filtration theory-determined values differed from experimentally determined values by less than 10%. In contrast, the responses of solute and bacteriophage tracers passing upwards through graded columns could not be reproduced with a single analytical solution. However, a flux-weighted summation of four one-dimensional advective–dispersive analytical terms approximated solute breakthrough curves. The prolonged tailing observed in the resulting curve resembled that typically generated from field-based tracer test data, reflecting the potential importance of textural heterogeneity in the transport of dissolved substances in groundwater. Moreover, bacteriophage deposition terms, determined from filtration theory, reproduced the T7 breakthrough curve once desorption and inactivation on grain surfaces were incorporated. To evaluate the effect of FU sequences on mass transport processes in more detail, bacteriophage passage through sequences resembling those sampled from a FU bed in a fluvioglacial gravel pit were carried out using an analogous approach to that employed in the laboratory. Both solute and bacteriophage breakthrough responses resembled those generated from field-based test data and in the graded column experiments. Comparisons with the results of simulations using averaged hydraulic conductivities show that simulations employing averaged parameters overestimate bacteriophage travel times and underestimate masses recovered and peak concentrations.

Influence of flow rate on transport of bacteriophage in shale saprolite.

The objective of this study was to investigate the influence of flow rate on transport and retention of bacteriophage tracers in a fractured shale saprolite, which is a highly weathered, fine-grained subsoil that retains much of the fabric of the parent bedrock. Synthetic ground water containing PRD-1, MS-2, and bromide was passed through a saturated column of undisturbed shale saprolite at rates ranging from 0.0075 to 0.96 m d '. First arrival of the bacteriophage tracers in effluent samples in each of the experiments occurred within 0.01 to 0.04 pore volumes (PV) of the start of injection, indicating that bacteriophage were advectively transported mainly through fractures or macropores. Bacteriophage transport velocities, based on first arrival in the effluent, were very similar to fracture flow velocities calculated using the cubic law for flow in a fractured material. For MS-2, maximum concentration and mass of tracer recovered both increased steadily as flow rate increased. For PRD-1, these values initially increased, but were nearly constant at flow rates above 0.039 m d(-1), indicating that approximately 50% of the observed losses were independent of flow rate. Evaluation of the data indicates that physical straining and electrostatic or hydrophobic attachment to fracture or macropore walls were the dominant retention processes. Inactivation and gravitational settling playing secondary roles, except at the slowest flow rates. The study suggests that microbial contamination from sources such as septic fields and sewage ponds may pose a threat to the quality of ground water and surface water in areas with saprolitic subsoils.

Kinetic modeling of virus transport at the field scale

Bacteriophage removal by soil passage in two field studies was re-analyzed with the goal to investigate differences between one- and two-dimensional modeling approaches, differences between one- and two-site kinetic sorption models, and the role of heterogeneities in the soil properties. The first study involved removal of bacteriophages MS2 and PRD1 by dune recharge, while the second study represented removal of MS2 by deep well injection. In both studies, removal was higher during the first meters of soil passage than thereafter. The software packages HYDRUS-1D and HYDRUS-2D, which simulate water flow and solute transport in one- and two-dimensional variably saturated porous media, respectively, were used. The two codes were modified by incorporating reversible adsorption to two types of kinetic sites. Tracer concentrations were used first to calibrate flow and transport parameters of both models before analyzing transport of bacteriophages. The one-dimensional one-site model did not fully describe the tails of the measured breakthrough curves of MS2 and PRD1 from the dune recharge study. While the one-dimensional one-site model predicted a sudden decrease in virus concentrations immediately after the peaks, measured data displayed much smoother decline and tailing. The one-dimensional two-site model simulated the overall behavior of the breakthrough curves very well. The two-dimensional one-site model predicted a more gradual decrease in virus concentrations after the peaks than the one-dimensional one-site model, but not as good as the one-dimensional two-site model. The dimensionality of the problem hence can partly explain the smooth decrease in concentration after peak breakthrough. The two-dimensional two-site model provided the best results. Values for k att2 and k det2 could not be determined at the last two of four monitoring wells, thus suggesting that either a second type of kinetic sites is present in the first few meters of dune passage and not beyond the second monitoring well, or that effects of soil heterogeneity and dimensionality of the problem overshadowed this process. Variations between single collector efficiencies were relatively small, whereas collision efficiencies varied greatly. This implies that the nonlinear removal of MS2 and PRD1 is mainly caused by variations in interactions between grain and virus surfaces rather than by physical heterogeneity of the porous medium. Similarly, a two-site model performed better than the one-site model in describing MS2 concentrations for the deep well injection study. However, the concentration data were too sparse in this study to have much confidence in the fitted parameters.

Transport and retention of bacteriophages in two types of willow‐cropped lysimeters

Irrigation and fertilization of short‐rotation willow coppice with wastewater is a new way of reusing wastewater in Sweden. To evaluate the possible impact of viruses on groundwater quality, the transport and retention of the bacteriophage Salmonella Typhimurium type 28B were studied in two types of willow‐cropped field lysimeters containing clay or sand soil. Phages were applied to the soil surface and moderate irrigation was done daily under field‐like conditions. In the clay, soil rapid transport of bacteriophages was recorded with breakthrough at 1,2‐m depth after 2–24 hours indicating macropore flow through the soil. Phage transport through the sand soil varied considerably, but was in general much slower and the phage retention much higher compared with the clay soil. The willow plants were not found to facilitate phage leaching. Instead, the results indicate the presence of phage retaining processes in the rhizosphere.

Viral tracer studies indicate contamination of marine waters by sewage disposal practices in key largo, Florida

Domestic wastewater disposal practices in the Florida Keys are primarily limited to on-site disposal systems such as septic tanks, injection wells, and illegal cesspits. Poorly treated sewage is thus released into the highly porous subsurface Key Largo limestone matrix. To investigate the fate and transport of sewage in the subsurface environment and the potential for contamination of marine surface waters, we employed bacteriophages as tracers in a domestic septic system and a simulated injection well in Key Largo, Florida. Transport of bacteriophage (Phi)HSIC-1 from the septic tank to adjacent surface canal waters and outstanding marine waters occurred in as little as 11 and 23 h, respectively. Transport of the Salmonella phage PRD1 from the simulated injection well to a canal adjacent to the injection site occurred in 11.2 h. Estimated rates of migration of viral tracers ranged from 0.57 to 24.2 m/h, over 500-fold greater than flow rates measured previously by subsurface flow meters in similar environments. These results suggest that current on-site disposal practices can lead to contamination of the subsurface and surface marine waters in the Keys.

Effect of pH on bacteriophage transport through sandy soils

Effects of pH and hydrophobicity on attachment and detachment of PRD- 1 and MS- 2 in three different sandy soils were investigated in a series of laboratory-column experiments. Concentrations of the lipid-containing phage PRD- 1 decreased 3–4 orders of magnitude during passage through the 10–15-cm-long columns. Attachment of the lipid-containing phage PRD- 1 was insensitive to pH and was apparently controlled by hydrophobic interactions in soil media. The less-hydrophobic phage MS-2 acted conservatively; it was not removed in the columns at pH's 5.7–8.0. The sticking efficiency (α) in a colloid-filtration model was between 0.1 and 1 for PRD- 1, indicating a relatively high removal efficiency. Phage attachment was reversible, but detachment under steady-state conditions was slow. An increase in pH had a moderate effect on enhancing detachment. Still, these soils should continue to release phage to virus-free water for days to weeks following exposure to virus-containing water. In sandy soils with a mass-fraction organic carbon as low as a few hundredths of a percent, pH changes in the range 5.7–8.0 should have little effect on retention of more-hydrophobic virus (e.g., PRD- 1), in that retardation will be dominated by hydrophobic effects. Sharp increases in pH should enhance detachment and transport of virus previously deposited on soil grains. A more hydrophilic virus (e.g., MS- 2) will transport as a conservative tracer in low-carbon sandy soil.

Bacteriophage Transport in Sandy Soil and Fractured Tuff

Bacteriophage transport was investigated in laboratory column experiments using sandy soil, a controlled field study in a sandy wash, and laboratory experiments using fractured rock. In the soil columns, the phage MS-2 exhibited significant dispersion and was excluded from 35 to 40% of the void volume but did not adsorb. Dispersion in the field was similiar to that observed in the laboratory. The phage f2 was largely excluded from the porous matrix of the two fractured-rock cores studied, coming through 1.2 and 2.0 times later than predicted on the basis of fracture flow alone. Because of matrix diffusion, nonsorbing solutes were retarded by over a factor of three relative to fracture flow. The time for a solute tracer to equilibrate with the porous matrix of 6.5-cm-diameter by 25-cm-long cores was measured in days. Results of both granular-medium and fractured-rock experiments illustrate the inability of a solute tracer to provide estimates for dispersion and effective porosity that are applicable to a colloid. Bacteriophage can be used to better estimate the maximum subsurface transport rate of colloidal contaminants through a porous formation.