The association of viruses with settling particles is certainly a major process controlling the spread of viral pollution in surface water and sediment. To better understand the viral distribution in a river system, the behavior of F-specific RNA bacteriophages (FRNAPHs) was investigated in relationship with the suspended solids and sediment. The partitioning of phage particles (free or associated with solids) in surface water and the attachment capabilities of eight distinct strains of phages to sediment were studied in lab experiments. In situ observations were also performed with the genotyping of 166 individual plaques of FRNAPHs isolated from surface water and sediment. The results reported here demonstrate a variation of the status of infectious phages as a function of the hydro-climatological conditions. Phage-solid association seems to mainly occur during the peak of rainfall-runoff events but also to a certain extent during the recession phase compared to low flow conditions. The transfer of phages from the water column to sediment may occur at this time. Furthermore, the ability of FRNAPHs to interact with sediment was established for six strains out of eight, belonging to genogroups II, III and IV. A similar dynamic was observed for strains within a same genogroup despite different intensity of attachment and inactivation rates for strains of genogroups III and IV. The latter results match the in situ observations in the water and sediment compartments of the studied area. Infectious FRNAPH genogroup II was more abundant in sediment than in surface water. Its capability to sorb to sediment and its higher persistence in the environment compared to genogroups III and IV were the two main explanations. Together, lab and in situ experiments produce an overall vision of the mechanisms governing FRNAPH distribution among the water column and riverbed sediment.
Heavy rainfall events were previously reported to bring large amounts of microorganisms in surface water, including viruses. However, little information is available on the origin and transport of viral particles in water during such rain events. In this study, an integrative approach combining microbiological and hydrological measurements was investigated to appreciate the dynamics and origins of F-specific RNA bacteriophage fluxes during two distinct rainfall-runoff events. A high frequency sampling (automatic sampler) was set up to monitor the F-specific RNA bacteriophages fluxes at a fine temporal scale during the whole course of the rainfall-runoff events. A total of 276 rainfall-runoff samples were collected and analysed using both infectivity and RT-qPCR assays. The results highlight an increase of 2.5 log10 and 1.8 log10 of infectious F-specific RNA bacteriophage fluxes in parallel of an increase of the water flow levels for both events. Faecal pollution was characterised as being mainly from anthropic origin with a significant flux of phage particles belonging to the genogroup II. At the temporal scale, two successive distinct waves of phage pollution were established and identified through the hydrological measurements. The first arrival of phages in the water column was likely to be linked to the resuspension of riverbed sediments that was responsible for a high input of genogroup II. Surface runoff contributed further to the second input of phages, and more particularly of genogroup I. In addition, an important contribution of infectious phage particles has been highlighted. These findings imply the existence of a close relationship between the risk for human health and the viral contamination of flood water.
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