Phage Induction of Lysogenic Rhizobium leguminosarum biovar trifolii in both the Free-living and the Symbiotic Form

Abstract

A lysogenic strain, Rhizobium leguminosarum biovar trifolii UK-1: φU, was isolated from a wild white clover nodule. It was symbiotically effective on white clover. A lysogenic phage (U-mole) was induced from this strain by treatment with either UV irradiation or mitomycin C. Phage U-mole had an icosahedral head (40 nm wide), a short tail (9 nm long) and tail fibres (15 nm long). Phage U-mole was induced with mitomycin C both from bacterial cells in infection threads and from bacteroids in nodules. Southern hybridization using EcoRI fragments of phage U-mole as probe indicated that phage U-mole DNA was integrated into the chromosome of strain UK-1: øU at a site involving the 60 kb EcoRI fragment of phage U-mole. Phage U-mole also lysogenized the wild-type strain R. leguminosarum biovar trifolii 4S. The resulting lysogenized strain, 4S:øU, had lost its 315 kb Sym plasmid and its nodulation ability.