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Abstract
SUMMARY: Magnesium or certain other divalent metal ions are needed for the adsorption of phage anti-R to its host, a ‘rough’ strain of Salmonella typhi. In medium containing magnesium ions the infected organisms burst after a latent period of about 20 min. at 37° but when infected organisms are diluted into medium without added divalent metal ions phage growth is considerably inhibited. A rapid increase in phage titre occurs when magnesium ions are added late, i.e. at some time after the end of the normal latent period, to dilute cultures of phage-infected organisms. During the interval between infection and this late addition of magnesium ions no appreciable numbers of infective intracellular phage were detected after ultrasonic disruption of the organisms. It is concluded that in addition to being an adsorption cofactor, magnesium functions at some late stage in phage development. Phage anti-R is probably related to ϕX 174; it consists of particles approximately 30 mμ in diameter and the intact phage reacts similarly with formaldehyde.
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