Understanding Viral Impacts in Soil Microbial Ecology Through the Persistence and Decay of Infectious Bacteriophage Particles

Marine bacteriophages have been well characterized in terms of decay rates, population dynamics in relation to their hosts, and their impacts on biogeochemical cycles in the global ocean. Knowledge on soil bacteriophage ecology lags considerably behind, with few studies documenting population dynamics with hosts and even fewer reporting decay rates. By using sterile soil or freshwater microcosms inoculated with a single bacteriophage stock, then extracting the phage at multiple time points and plating the sample using plaque assays, I was able to quantify loss of infectivity over time for phages, independent of host interactions, for five different model phages. When studied over multiple weeks, decay rates ranged from 0.07% h-1 for a natural soil phage in freshwater to 0.60% h-1 for a freshwater phage in soil microcosms. When studied over a short duration, decay rates for a Bacillus subtilis phage were 3.3% h-1 over 72 h and a Bacillus licheniformis phage was 14.38% h-1 over 42 hours. Slower rates of phage decay in soils indicate a lower turnover rate, which may have subsequent and potentially far-reaching impacts on virus-mediated mortality and bacterial activity. The wide range of decay rates observed in the present study and the lack of information on this critical aspect of virus-host dynamics in soil emphasizes the need for continued research in this field