FINAL PROOF FOR THE IDENTITY OF ENZYMIC SPECIFICITIES OF EGG-WHITE LYSOZYME AND PHAGE T2 ENZYME

Characterization of a bacteriophage-induced, host-specific lytic enzyme from lysates of Bacillus stearothermophilus infected with bacteriophage TP-8

Phage TP-8 lysates of Bacillus stearothermophilus 4S or 4S(8) contain lytic activity exhibiting two pH optima, one at pH 6.5 and the other at pH 7.5. Using a variety of fractionation procedures, the two lytic activities could not be separated. At pH 7.5 the lytic enzyme is an endopeptidase which hydrolyzes the l-alanyl-d-glutamyl linkage in the peptide subunits of the cell wall peptidoglycan and at pH 6.5 it exhibits N-acetylmuramidase activity. Endopeptidase activity is inhibited by NaCl and neither lytic activity was significantly affected by divalent cations or ethylenediaminetetraacetic acid. Crude lysates contain 2.5 to 3.0 times more endopeptidase activity than N-acetylmuramidase activity. The ratio of the two lytic activities (endopeptidase/N-acetylmuramidase) changes to 1.3 to 1.7 during the course of purification, to 1.0 after isoelectric focusing, and 3.9 and 6.00 after exposure for 2 h at 60 and 65 C, respectively. We conclude that the two lytic activities may be associated with a single protein or a lytic enzyme complex composed of two enzymes. Lytic activity at pH 7.5 is more effective in solubilizing cells or cell walls than the lytic activity at pH 6.5. LiCl extracts of 4S and 4S(8) cells contain lytic activity exhibiting endopeptidase activity at pH 7.5 and N-acetylmuramidase activity at pH 6.5. Lytic activity in these LiCl extracts also has a number of other properties in common with those in lysates of phage TP-8. We proposed that the lytic enzyme(s) are not coded for by the phage genome but are part of the host autolytic system.

Mode of host cell penetration by bacteriophage phi X174

Bacteriophage phiX174 is an icosahedral phage which attaches to host cells without the aid of a complex tail assembly. When phiX174 was mixed with cell walls isolated from the bacterial host, the virions attached to the wall fragments and the phage deoxyribonucleic acid (DNA) was released. Attachment was prevented if the cell walls were treated with chloroform. Release of phage DNA, but not viral attachment, was prevented if the cell walls were incubated with lysozyme or if the virions were inactivated with formaldehyde. Treatment of the cell walls with lysozyme released structures which were of uniform size (6.5 by 25 nm). These structures attached phiX174 at the tip of one of its 12 vertices, but the viral DNA was not released. The virions attached to these structures were oriented with their fivefold axis of symmetry normal to the long axis of the structure. No virions were attached to these structures by more than one vertex. Freeze-etch preparations of phiX174 adsorbed to intact bacteria showed that the virions were submerged to one half their diameter into the host cell wall, and the fivefold axis of symmetry was normal to the cell surface. A second cell could not be attached to the outwardly facing vertex of the adsorbed phage and thus the phage could not cross-link two cells. When the virions were labeled with (3)H-leucine, purified, and adsorbed to Escherichia coli cells, about 15% of the radioactivity was recovered as low-molecular-weight material from spheroplasts formed by lysozyme-ethylenediaminetetraacetic acid. Other experiments revealed that about 7% of the total parental virus protein label could be recovered in newly formed progeny virus.

Purification and physical properties of group C streptococcal phage-associated lysin

A purification procedure for the Group C phage-associated lysin is described utilizing tetrathionate to protect the enzyme's -SH group(s) from thiol-inactivating agents. A 652-fold purification has been accomplished yielding a solution in which the enzyme activity corresponds to essentially a single band on polyacrylamide gel which accounts for 70% of the total protein in the preparation. A molecular weight of 101,000 and frictional ratio of 1.526 was determined for the lysin utilizing experimentally determined values for its Stokes radius and sedimentation coefficient.

Purification and properties of a thermophilic bacteriophage lytic enzyme

A phage lytic enzyme was isolated from lysates of Bacillus stearothermophilus (NCA 1503-4R). The enzyme was purified 1,998-fold with a 27% recovery of enzyme activity. By use of polyacrylamide gel electrophoresis and sucrose gradient centrifugation the enzyme was judged free from protein contaminants. The lytic enzyme was active over a pH range of 6.0 to 7.0, with a maximum at 6.3, and it was stable between pH 7.0 and 8.0 and at 5.0 and unstable between pH 5.5 and 6.5. The temperature coefficient (Q(10)) was 2.27 between 35 and 45 C, 2.01 between 45 and 55 C, and 2.00 between 50 and 60 C. Lytic enzyme in 0.1 m sodium phosphate was not inactivated after a 1-hr exposure to temperatures below 65.5 C, whereas a 1% inactivation was observed at 70.6 C. A 2-hr exposure at 60.1, 65.5, and 70.6 C resulted in an inactivation of 1.2, 9.6, and 12.0%, respectively. A sodium phosphate concentration of at least 0.1 m was necessary for the prolonged exposure of lytic enzyme at 55 C (pH 6.3), whereas 0.005 m was required for maximal lytic activity. Lytic activity was stimulated 169, 165, and 160% by 10(-4)m Mg(++), Ca(++), and Mn(++), respectively. Lytic activity was inhibited 75% by 10(-4)m ethylenediaminetetraacetic acid (EDTA). The EDTA inhibition could be reversed by the addition of excess Mg(++), Ca(++), or Mn(++). Lytic activity was not affected by NaCl, KCl, or NH(4)Cl. Lytic activity was inhibited 100, 91, 25, 61, and 56% by 10(-4)m Hg(++), Cu(++), Zn(++), p-chloromercuribenzoate, and p-hydroxymercuribenzoate, respectively. Cysteine or 2-mercaptoethanol did not stimulate lytic activity, nor were these sulfhydryl compounds required for maintenance of enzyme activity during handling or storage. Cell walls were rapidly solubilized when incubated with lytic enzyme. Lytic action was complete after 1.5 min, with a 70% reduction in optical density (OD). Cell walls without lytic enzyme showed no reduction in OD during this period. The solubilization of N-terminal amino groups paralleled the reduction in OD and reached a level of 0.3 mumole/mg of cell wall after 4 min of incubation. Cell walls with and without lytic enzyme treatment showed a 3- and a 1.3-fold increase, respectively, in N-terminal amino groups after 3 hr of incubation. There was no release of reducing power in either the untreated cell wall suspensions or those treated with lytic enzyme. Electron micrographs of treated and untreated cell walls showed that the enzyme partially degrades the cell wall with the release of small wall fragments.

Polysaccharide depolymerase associated with bacteriophage infection

Bartell, Pasquale F. (University of Pennsylvania, Philadelphia), Thomas E. Orr, and Grace K. H. Lam. Polysaccharide depolymerase associated with bacteriophage infection. J. Bacteriol. 92:56-62. 1966.-A recently isolated bacteriophage of Pseudomonas aeruginosa was observed, in association with bacteria, to produce a polysaccharide depolymerase. Exposure of slime polysaccharide to the enzyme at the pH optimum of 7.5 for 30 to 60 min resulted in a decreased viscosity of 20 to 25%, and a measurable increase in the levels of hexosamines, hexoses, and reducing substances, distinguishing it from other phage-associated depolymerases. Like egg-white lysozyme, the depolymerase produced a clearing of mature bacterial lawns, but was shown to be devoid of muralytic activity by turbidimetric and paper chromatographic analysis. The depolymerase reacted with polysaccharides of only certain strains of P. aeruginosa, and there appeared to be no correlation with phage susceptibility. The enzyme was not detectable in uninfected cultures, nor was it synthesized when infection was initiated by phages other than phage 2. The available data suggest that the genetic information required for biosynthesis of this enzyme is furnished by the phage 2 genome.