GROUP N STREPTOCOCCAL PHAGE LYSIN.

Abstract

Two stages of phage multiplications, the adsorption-penetration process and the lysis of the host, have recently been largely elucidated. For some time it has been postulated that an enzyme attached to, or contained in, the phage tail is involved in the adsorption process with at least some phage-host systems. Similarly, the earliest discovered effect of a lytic phage, namely the liberation of the mature phage particles (lysis of the host), is due to a lytic enzyme acting on the cell wall. Bronfenbrenner & Muckenfuss (1927) recognized that phage lysates contain a substance other than phage. This ‘ ferment-like ’ substance differed from phage because it only affected dead staphylococci. It was adsorbed to clay filters, inactivated on standing at room temperature, it was more heat labile than phage, and did not diffuse through collodion membranes. This description adequately fits the staphylococcal virolysin (or phage lysin) described by Ralston, Beer, Lieberman & Krueger (1955) which lysed only dead cells, although viable cells were lysed in the presence of the homologous phage. Brown (1956) showed that phage-free lysates of coliphage T, could dissolve cells of Eschterichia coli killed with chloroform, and Koch & Jordan (1957) demonstrated a free enzyme in T, phage lysates. Koch & Dreyer (1958) came to the conclusion that the phage lysin was a lysozyme. This was confirmed by Weidel & Katz (1961) and K,atz & Weidel (1961) who purified both the bound and free coli T, phage enzymes; and Murphy (1960), working on similar lines, found that the bound and free ‘ megaterium ’ enzymes differed only in their pH optima. Halo1 formation was observed by Naylor & Czulak (1956) with a lactic acid streptococcal phage, and by Murphy (1957; 1960) with Bacillus megaterium phage. They found that halos were due to an enzyme affecting the dead cells surrounding the phages without giving complete lysis. Murphy demonstrated that the enzyme was resistant to trypsin, pepsin, DNA-ase and RNA-ase but was inactivated by chymotrypsin. It is possible that the inhibition of a rhizobium phage by chymotrypsin reported by Kleczkowsky & Kleczkowsky (1954) may be due to the inhibition of a similar phage enzyme. Halo formation due to cell-wall lysis differs from the halos observed around plaques of mucoid strains of Escherichia coli by Sertic (1929), and since reported to occur with many other organisms. In these cases the halo is due to an enzyme hydrolysing capsular polysaccharides (Adams & Park, 1956). Other aspects of the action of phage lysin are the ‘nascent’ phage phenomenon and ‘lysis from without’. Nascent phage was first observed by Evans (1934) and shown by Maxted (1957) to be due to an enzyme liberated from the host at the same time as the phage. When some phages, e.g. coliphage T,, are adsorbed to their host