SUMMARY: Clupein at 0·02-0·05% in the liquid nutrient medium used to cultivate nodule bacteria, rapidly killed the bacteria and slowly inactivated a bacteriophage that attacked them. When added to a bacterial culture in liquid medium before adding phage, clupein prevented phage and bacteria from combining; when added after the two had combined, clupein interrupted further stages of phage-host interaction. Clupein at 0·0016% acted bacteriostatically and slowed phage multiplication but did not stop it. Trypsin and chymotrypsin hydrolyse clupein, trypsin breaking about twice as many peptide bonds as chymotrypsin. At a concentration corresponding to 0·02-0·05% clupein, the peptides produced by chymotrypsin acted bacteriostatically in the liquid nutrient medium; the peptides inactivated phage much more slowly than did intact clupein, and they inhibited phage multiplication by interfering with the combination between phage and host. When added after phage and bacteria had combined, the peptides did not interfere with further stages of phage-host interaction. The smaller peptides produced by trypsin had no effect on host bacteria, phage, or phage/host interaction.

Phage preparations partially inactivated by clupein had their activity partially restored by incubation with trypsin or chymotrypsin.

Clupein, but none of its hydrolytic products, made phage with much non-phage material sedimentable by slow-speed centrifugation.


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