Specific Dissociation of Phage Xp12 by Sodium Citrate

In general, a low concentration (0.003 m) of citrate ion has little or no effect on phage stability, but concentrations greater than this accelerate phage inactivation (Lark & Adams, 1953). When phage T5, suspended in 0.2 m-potassium solution, is heated at 55°, 90% is inactivated after incubation for 150 min. When 0.04 m-citrate is added, however, only 20 min. is required (Lark & Adams, 1953). The phage Xp12 from Xanthomonas oryzae, possessing an unusual base in its DNA (5-methylcytosine completely replaces cytosine) (Kuo, Huang & Teng, 1968a), was extremely sensitive to low concentrations of citrate. Because of this unusual property the mechanism of the effect of citrate on phage Xp12 was carefully studied; citrate specifically causes the separation of the head from the tail of this phage.

The conditions for growth and maintenance of Xanthomonas oryzae strain 507 are described in a previous paper (Kuo et al. 1968b).