Isolation and Characterization of Two Endogenous Phages of Rhodobacter sphaeroides

Institut für Mikrobiologie der Universität Göttingen, Grisebachstrasse 8, D-3400 Göttingen, FRG ABSTRACT SUMMARY: Two new temperate bacteriophages for Rhodobacter sphaeroides , designated RsA and RsD, were isolated from a stock of phage RsGl using R. sphaeroides strain DSM 159-2 as the indicator strain. Electron-microscopic examination showed that phage RsA belonged to group B and phage RsD belonged to group A of Bradley's morphological classification. Phage RsA had a polyhedral head (50 nm in diameter) and a long, flexible, non-contractile tail (250 by 11 nm). Phage RsD 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 RsA genome was about 40 kb and the G + C content was 72.4 mol%. The size of the RsD genome was about 56 kb and the G + C content was approximately 72.6 mol%. Biotinylated DNA probes of phage RsA and of phage RsD 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 RsA formed plaques on R. sphaeroides DSM 159-2 only, while phage RsD plaqued on another six strains of R. sphaeroides but not on R. capsulatus. Present address: Institut für Angewandte Mikrobiologie der Universität des Saarlandes, D-6600 Saarbrücken, FRG.