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Effects of Calcium on the Lytic Cycle of Bacillus subtilis Phage 41c

Department of Microbiology, University of New Hampshire, Durham, New Hampshire 03824 U.S.A.

The lytic cycle of Bacillus subtilis phage 41c required the presence of at least 10 mM-calcium. In the absence of this ion, the plaquing efficiency of the virus was reduced to less than 0.1. Likewise, replacement of Ca²⁺ with other divalent ions (Ba²⁺, Sr²⁺, Mg²⁺, Mn²⁺) resulted in reduced efficiencies.

Adsorption of 41c was Ca²⁺-dependent, requiring concentrations ranging from 0.1 to 10 mM. Although more than 90% of the phage adsorbed at 0.1 mM-Ca²⁺, successful infection could only be achieved at higher Ca²⁺ levels. Sub-optimal concentrations of the ion resulted in the loss of 90% of infected centres within 1 min after the initiation of infection, indicating an early post-adsorption ion requirement. Penetration experiments with ³²P-labelled phage DNA indicated that an irreversible inhibition of injection was occurring in the majority of the phage-bacterium complexes. A third level of cation involvement became apparent when phage-bacterium complexes in which penetration had occurred exhibited a greatly reduced burst size. The post-penetration ionic requirement occurred early in the infection process since dilution of infected complexes into Ca²⁺-free medium at 2.5 min p.i. resulted in reduced phage yields. The requirement was dispensable after 6 min p.i., since infected complexes diluted into Ca²⁺-free medium at this time exhibited a normal one-step growth curve. Analysis of messenger RNA production by molecular DNA-RNA hybridization techniques indicated that transcriptional events were similar in the presence and absence of Ca²⁺. At present, the identification of the third ion-dependent stage is unresolved.

^* Present address: Department of Energy and Environment, Brookhaven National Laboratory, Upton, New York 11973, U.S.A.

Received 19 March 1980; accepted 17 June 1980.