Cultures of str. 1 are persistently infected with the virulent and extremely halophilic phage Hs1. The nature of phage infection depended on the salt concentration in the medium, changing from lytic to persistent as the salt concentration increased from 17.5 to 30% (w/v) NaCl. At salt concentrations below 25% (w/v) NaCl, phage infection resulted in a lytic development with phage production. The lytic development was characterized by a constant eclipse and latent period, irrespective of bacterial growth rate or salt concentration. At salt concentrations above 25% (w/v) NaCl phage infection resulted in the establishment of a carrier state in which lysis of the infected bacteria was delayed for several generations. In this carrier state the infected bacteria continued to multiply at the same rate as uninfected cells. Bacteria infected under conditions favouring lytic development could survive if transferred to a medium which favoured the formation of carrier cells. More than 77% of the bacteria infected with phage in a medium containing 20% (w/v) NaCl were able to form colonies if plated 90 min p.i. on agar plates containing 30% (w/v) NaCl. A majority of the colonies carried phage.


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