Transport of marine tracer phage particles in soil

Longitudinal dispersivity and saturation of sand-clay mixtures: Impact of clay content, initial degree of saturation, and swelling potential

Dispersion plays a critical role in predicting solute transport through unsaturated soils. Therefore, this study comprehensively investigated the unsaturated longitudinal dispersivity of sand-clay mixtures using laboratory soil-column experiments. The effects of clay content, average degree of saturation, flow path length, and swelling potential on the unsaturated longitudinal dispersivity were examined. The longitudinal dispersivity was evaluated based on the observed breakthrough curves using the advection-dispersion equation. It was found that an increase in illite content, initial degree of saturation, flow path length, and swelling potential led to an increase in longitudinal dispersivity. In addition, the longitudinal dispersivity under saturated conditions was lower than when the initial average degree of saturation was 80 % whereas an increase in unsaturated longitudinal dispersivity as the initial degree of saturation increased from 20 to 80 % was observed. This observation led to a bilinear trend of longitudinal dispersivity as a function of the initial degree of saturation in sand-clay mixtures. The trend in the longitudinal dispersivity of sand-clay mixtures observed in this study differs from that reported in the literature for sand, suggesting the need for incorporating clay content, swelling potential, and initial degree of saturation when predicting the unsaturated longitudinal dispersivity of clay-containing soils.

Mycelia-Assisted Isolation of Non-Host Bacteria Able to Co-Transport Phages

Recent studies have demonstrated that phages can be co-transported with motile non-host bacteria, thereby enabling their invasion of biofilms and control of biofilm composition. Here, we developed a novel approach to isolate non-host bacteria able to co-transport phages from soil. It is based on the capability of phage-carrying non-host bacteria to move along mycelia out of soil and form colonies in plaques of their co-transported phages. The approach was tested using two model phages of differing surface hydrophobicity, i.e., hydrophobic Escherichia virus T4 (T4) and hydrophilic Pseudoalteromonas phage HS2 (HS2). The phages were mixed into soil and allowed to be transported by soil bacteria along the mycelia of Pythium ultimum. Five phage-carrying bacterial species were isolated (Viridibacillus sp., Enterobacter sp., Serratia sp., Bacillus sp., Janthinobacterium sp.). These bacteria exhibited phage adsorption efficiencies of ≈90-95% for hydrophobic T4 and 30-95% for hydrophilic HS2. The phage adsorption efficiency of Viridibacillus sp. was ≈95% for both phages and twofold higher than T4-or HS2-adsorption to their respective hosts, qualifying Viridibacillus sp. as a potential super carrier for phages. Our approach offers an effective and target-specific way to identify and isolate phage-carrying bacteria in natural and man-made environments.