Ubiquitous Bacteriophage Hosts In Rice Paddy Soil

Viruses are the most abundant biological entities in rice fields, and bacteriophages comprised the majority among viral communities. Sphingomonas/Novosphingobium phages were exclusively siphoviruses with various host ranges. The high frequency of phage-infected bacterial cells indicated that the bacterial mortality from phage lysis could be significant enough to redirect the microbial food web and change the bacterial communities. There was no significant difference in the frequency of lysogeny between oligotrophs and copiotrophs in soil. Superinfection immunity was not important for bacteria in rice fields, although slower growth from the burden of prophage DNA synthesis was indicated among strains at the genus or species level. The majority of the g23 sequences of T4-type bacteriophages in rice fields were distantly related to those of marine origins. Horizontal gene transfer was suggested by the identical g23 sequences found in distant rice fields. The g23 genes in rice fields have apparently diverged more compared with marine g23 genes.