Transport and Survival of Marine Tracer Phages in Topsoil at Field Conditions

Phages are ubiquitous in soil, shaping microbial diversity and nutrient cycling. Phage replication requires maintaining infectivity and finding the right host. Yet, there are limited data on phage persistence and transport in soil under field conditions. The potential presence of hosts enabling phage replication impedes the assessment of the mobility of autochthonous phages in soils. In lysimeters installed in forest and pasture topsoil, we elucidated the transport of the tailed marine <i>Pseudoalteromonas</i> phage HS2 in comparison to deuterium. Transport of infectious phages as well as numbers of tracer phage genomes and tracer capsid-bound genomes were quantified to account for phage retention and inactivation. Phages were transported up to 4 times faster than the simultaneously applied deuterium tracer, which was attributed to pore size exclusion. Retention in immobile regions and remobilization during precipitation caused pronounced tailing in tracer breakthroughs. High phage survival in pasture soil resulted in mass recoveries of infectious phages that were up to 6 times higher than those in forest soil. However, long-term observations showed that the infectivity was also preserved in forest soil, enabling event-driven remobilization. This remobilization underscores the importance of distinguishing between phage retention and inactivation, which is crucial for accurately predicting phage transport dynamics and their ecological impact in terrestrial environments.