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Title: A study of bacteriophage, with particular reference to a lysin-producing lactic streptococcal phage-host system
Author: Mullan, William Michael Anthony
ISNI:       0000 0001 3429 6848
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1982
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Paired and multi-strain cultures containing phage-unrelated strains of lactic streptococci are widely used in phage control schemes in cheese factories. Infection of such cultures with phage will not normally markedly affect acid production since the phage-resistant strains will continue to produce acid and enable cheese manufacture to continue. The work contained in this Thesis relates to a previously undocumented phage for str. lactis C2, phiC2(W), which when added to paired and multi-strain cultures containing C2 inhibits acid production. The phage was partially characterised with respect to host range, plaque morphology, latent period and burst size, particle morphology and the effect of temperature on replication. The phage which had a prolate polyhedral head had a short latent period (21 min) and was unusual in that it formed plaques surrounded by haloes. This latter property is indicative of a lysin-producing phage. phiC2(W) lysates of C2 were shown to contain a lytic agent which lysed both phage-sensitive and phage-insensitive lactic streptococci. An assay method for measuring lytic activity is described. The lytic agent was shown to be distinct from particulate phage. Centrifugation and acetone precipitation both reduced the level of phage (99 and 95% respectively) in phiC2(W) lysates without markedly affecting lytic activity. Lytic activity, but not phage, was destroyed by mild heat treatment and was lost after chromatography on the dye ligand Green A. Lytic activity, but not phage, could also be washed out of phiC2(W) lysates using ultrafiltration. Lytic activity was demonstrated in cells of C2 infected with phiC2(W) 10 min after infection and increased throughout the latent period reaching a high concentration at the rise period. Control cells or cells infected with phi712 did not demonstrate lytic activity. These results were interpreted as showing that the lytic activity in phiC2(W) lysates was phage induced and that phage lysin could be involved in the release of phage from infected cells. Experiments designed to determine the mechanism involved in the inhibition of acid production of paired and multi-strain cultures by phiC2(W) yielded evidence that the inhibition was due to the lysis of the non-homologous strains by a lytic enzyme released from phage-infected cells of C2. The significance of these results to starter selection for cheese-making and measures for controlling the nascent phenomenon are discussed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Bacteria in cheese production