Identification and characterization of phages parasitic on bradyrhizobia nodulating groundnut ( L.) in South Africa.

In this study, three lytic phages (namely, PRSA-1, PRSA-2 and PRSA-26) were isolated and characterized for their morphology, host range, profile and restriction endonuclease banding pattern of genome size. The susceptible rhizobial isolates were identified by H and II sequence analysis. The results showed that all phages had polyhedral head with non-contractile tail which confirmed their relationship with the family. All the three phages produced highly distinct plaques on their host bradyrhizobial lawn, and were highly sensitive to chloroform. The phage genome sizes ranged from 34.7 to 53.1 kbp. The phages were tested against groundnut-nodulating bradyrhizobial strains TUTAHSA75, TUTAHSA155 and TUTAHSA126 isolated from South African soils. The results revealed different bacterial susceptibilities to phages. Bradyrhizobial isolate TUTAHSA126 was susceptible to all three phages (i.e. PRSA-1, PRSA-2 and PRSA-26), TUTAHSA155 to two phages (i.e. PRSA-1, PRSA-2), and TUTAHSA75 to only one phage (i.e. PRSA-1). Phylogenetic analysis of H and II gene sequences of the phage-susceptible bradyrhizobial isolates revealed their close relatedness to a diverse group of species. Phage PRSA-1 could parasitize on all three bradyrhizobial strains, which indicates its potential role in horizontal gene transfer through lysogenic conversion, and/or genetic transduction in soil microbial environments.