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Appl Environ Microbiol. 1971 April; 21(4): 633-638
Copyright © 1971 American Society for Microbiology. All Rights Reserved.

Inhibition of the Plaquing Efficiency of T4r⁺ Bacteriophage by Subtilisin ¹

Department of Biology, Rensselaer Polytechnic Institute, Troy, New York 12181

ABSTRACT

The mechanism by which the replicative cycle of T4r⁺ phage is inhibited by certain nonhost bacterial systems was investigated. Some Bacillaceae, especially Bacillus subtilis, decreased the plaquing efficiency of this virus more than 95% within 24 hr of exposure. Sarcina lutea and Micrococcus sp. both failed to cause any significant change in the infectivity of T4r⁺ phage. Preliminary investigations into the nature of the inhibitory substance(s) suggested that an extracellularly elicited protein was at least partially responsible for this effect. Further analysis has implicated subtilisin, an exoprotease from B. subtilis, as the cause of some, if not all, of the observed decrease in plaquing efficiency. Gel-filtration chromatography of control and treated ¹⁴C-labeled T4r⁺ phage showed a wide dispersal of phage-specific material of these particles after 24 hr of exposure to pure subtilisin or to expended medium exoprotease from B. subtilis. It was concluded that B. subtilis exoprotease is capable of chemically altering the structure of the phage capsid, thus causing a decrease in its plaquing efficiency.

From a section of a dissertation submitted by the senior author in partial fulfillment of the requirements for the Ph.D degree in Biology at Rensselaer Polytechnic Institute. Parts of this work were presented at the Xth International Congress for Microbiology, Mexico City, Mexico, and the 160th American Chemical Society Meeting, Chicago, Ill.