Soil pH influences the composition of bacteriophage communities infecting individual hosts

Bacteriophages (phages) can infect a range of hosts in highly diverse soil bacterial communities. However, selection of host communities across ecological gradients and co-evolutionary processes may influence both the distribution of phages and the susceptibility of individual hosts through virus interactions and local adaptation within distinct ecological niches. Metagenomic-based analyses have revealed that soil pH selects for distinct populations and community structures for both phage and hosts at local and global scales. However, whether contrasting soil pH represents a selective barrier for phages capable of infecting an individual host is unknown. To examine the influence of pH on individual host-virus interactions, two closely related Bacillus strains were isolated and characterized from pH 7.5 soil associated with a long-term contiguous pH gradient (pH 4.5 to 7.5). Phages infecting each strain were subsequently enriched from soils across the pH gradient (pH 4.5, 5.5, 6.5 and 7.5), enumerated using a plaque assay, and characterized via metagenomic analysis. Phages infecting each strain were cultivated from all soils but their community composition and abundance varied with pH. Phage populations infecting each of the two strains were distinct despite the close relatedness of the two hosts, indicating relatively narrow host ranges for each virus. These results suggest that while phage community structures vary substantially across an ecological gradient, soil pH alone does not represent a barrier for the distribution of phages capable of infecting an individual host.