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Effect of spermine on host-cell lysis and reproduction by a lactic streptococcal bacteriophage
Abstract:
A method was tested for protecting a Streptococcus lactis strain, ML3, used as a starter in the manufacture of Cheddar cheese, against the lytic activity of its homologous phage, ml(3). At a concentration of 10(-2)m, a naturally occurring polyamine, spermine, in the form of its hydrochloride, protected ML3 against lysis-from-without and lysozyme activity and against lysis by the phage when added at the time of infection or up to 21 min after infection. It was found that the latter protective effect could be accounted for in terms of the spermine preventing the formation of mature particles rather than preventing the escape of viable phage. Single colonies selected from a culture of ML3 cells that had been previously infected with phage ml(3), in the presence of spermine, were all found to have acquired resistance to phage ml(3). They retained this resistance during a 3-month period of daily subculture in broth and, in the absence of spermine, could not be induced to liberate phage or phage components either by the techniques normally used for inducing lysogens or by artificial disruption of the cells. It is concluded that when spermine is added to ML3 cells before a certain critical stage of the phage infection cycle, the process of phage synthesis is irreversibly halted and the cells retain the infecting phage as a defective prophage that confers on the cells immunity to infection by the homologous phage. Phage-resistant cultures did not inherit reduced starter activity in association with their acquired resistance characteristic.
Insights
Spermine protects Streptococcus lactis ML3 starter cultures from phage lysis by halting phage synthesis. This results in phage-resistant cells that retain starter activity, crucial for Cheddar cheese production.
Area of Science:
- Microbiology
- Bacteriology
- Virology
Background:
- Bacteriophage lysis poses a significant threat to starter cultures in dairy fermentation.
- Streptococcus lactis ML3 is a key starter strain in Cheddar cheese manufacturing.
- Protecting starter cultures from phage infection is vital for consistent cheese production.
Purpose of the Study:
- To investigate the protective effect of spermine against homologous phage lysis in Streptococcus lactis ML3.
- To understand the mechanism by which spermine confers phage resistance.
- To assess the stability and impact of spermine-induced resistance on starter culture activity.
Main Methods:
- Treatment of Streptococcus lactis ML3 with spermine hydrochloride at various stages of phage ml(3) infection.
- Analysis of phage particle formation and release.
- Selection and subculturing of phage-resistant colonies.
- Induction assays for lysogeny and phage component release.
Main Results:
- Spermine (10(-2)m) protected ML3 against phage lysis, lysozyme activity, and lysis-from-without.
- Protection was effective when spermine was added during infection or up to 21 minutes post-infection.
- Spermine prevented mature phage particle formation, not phage escape.
- Phage-infected cells in the presence of spermine developed stable resistance to homologous phage.
- Resistant cultures did not exhibit reduced starter activity.
Conclusions:
- Spermine acts as a protective agent by irreversibly halting phage synthesis before a critical infection stage.
- This leads to the formation of defective prophages, conferring immunity to homologous phage infection.
- Spermine-induced phage resistance in starter cultures is stable and does not impair dairy fermentation capabilities.