MUTUAL EXCLUSION BETWEEN RELATED PHAGES

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Abstract
Bacteria infected with phage T2r+ are stimulated to exclude superinfecting phage T2r arriving after a time interval, and vice versa. The superinfacting phage is excluded in 50% of the bacteria if the time interval between infections is one minute. This time scale is similar to the one established by French et al. (1951) for the disruption of the nucleic acid of superinfecting phage. T2 irradiated with ultraviolet for 380 sec. leads to this stimulation to exclude superinfecting phage at nearly the same rate as does active phage. When the active phage is added simultaneously to the bacteria the inactive phage does not exclude it. If both the primary and the superinfecting phage have been inactivated by irradiation with ultra-violet, the ability of the superinfecting phage to cooperate with the primary phage in multiplicity reactivation drops off at the same rate at which the stimulation to exclusion is manifested. Under conditions which permit multiplicity reactivation to occur, the genetic markers of both parents enter into the progeny, i.e., both parents are reactivated in at least 50% of the cases. The stimulation to exclusion is dependent on processes requiring an external energy supply. It is practically absent in resting bacteria in buffer. The relationship between this exclusion, the nucleic acid breakdown observed by French et al., and the destruction of chromatinic bodies of infected bacteria (Luria and Human, 1950) is discussed.