Isolation and Characterization of Two Endogenous Phages of Rhodobacter sphaeroides

Abstract

Two new temperate bacteriophages for Rhodobacter sphaeroides, designated ϕRsA and ϕRsD, were isolated from a stock of phage ϕRsGl using R. sphaeroides strain DSM 159–2 as the indicator strain. Electron-microscopic examination showed that phage ϕRsA belonged to group B and phage ϕRsD belonged to group A of Bradley’s morphological classification. Phage ϕRsA had a polyhedral head (50 nm in diameter) and a long, flexible, non-contractile tail (250 by 11 nm). Phage ϕRsD also had a polyhedral head (56 nm in diameter) and a sheathed contractile tail (160 by 18 nm). Both phages contained double-stranded DNA with cohesive ends. The size of the ϕRsA genome was about 40 kb and the G + C content was 72·4 mol%. The size of the ϕRsD genome was about 56 kb and the G + C content was approximately 72·6 mol%. Biotinylated DNA probes of phage ϕRsA and of phage ϕRsD hybridized to genomic DNA from R. sphaeroides strains Y and Si 4 but not to DNA from other sources. The host ranges of the two phages were determined using 26 R. sphaeroides strains and six strains of Rhodobacter capsulatus. Phage ϕRsA formed plaques on R. sphaeroides DSM 159–2 only, while phage ϕRsD plaqued on another six strains of R. sphaeroides but not on R. capsulatus.