Mapping pathways of possible phage-mediated genetic interchange among soil bacilli

Bacillus pumilus (Strain W43) has been shown to sustain the growth of an unusually large number of different phages. From 22 isolates 16 distinguishable phages have been obtained. Phage BPPX which is similar to the defective particle PBSX of B. subtilis is induced by four of the phages. When tested against a variety of Bacillus spp 12 of the non-defective phages had host ranges crossing at least one species line: Phage K13 infected 14 of 25 strains, distributed among six species some of which are considered to be taxonomically distant. It is suggested that the relatively restricted host ranges noted for most Bacillus phages may result from the use. as test organisms, of bacteria isolated from soils ecologically distinct from the source(s) of phage. A genetic “circuit diagram” constructed from the host range table, maps possible genetic connexions between various soil bacilli made possible by the phages. These data are set in the context of recent theories which postulate that viruses are agents of accelerated cell evolution.