Browsing by Subject "happipitoisuus"

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  • Niemi, Justiina (Helsingin yliopisto, 2020)
    Propionibacterium freudenreichii is a dairy propionic acid bacterium and it is used as adjunct culture in Swiss-type cheese manufacture. The bacterial strain is known for its GRAS (Generally Recognized as Safe) status, and it is safe to use in food. Based on previous studies, P. freudenreichii requires anaerobic conditions to start bacterial growth. Bacterial viruses ‘bacteriophages’ uses two life cycles, lysogenic or lytic cycle. The life cycle of bacteriophages affects bacterial cell lysis or division. Researchers are interested in fortifying foods naturally with vitamin B12. P. freudenreichii is known for its ability to actively produce vitamin B12. This master's thesis aims were to study 1) The effect of oxygen contentration on Propionibacterium freudenreichii subsp. freudenreichii JS7 strain and 2) the effect of oxygen consentration on the prevalence of bacteriophage in P. freudenreichii JS7 strain. In this study, P. freudenreichii JS7 strain was grown at different oxygen concentrations. Bacterial growth was observed by cell density measurements and cell plating. In the preliminary experiment, the strain was grown 1) anaerobically 2) two stages which includes aerobic and anaerobic growth conditions and 3) aerobically. Based on the partial results of the preliminary experiment, the fermentation was performed in a bioreactor in an anaerobic growth condition. The cell plating results of the bioreactor experiment were used to study the effect of oxygen concentration on the presence of bacteriophage in a bacterial strain by using three primer pairs. The polymerase chain reaction was applied to study the presence of the bacteriophage genome as a plasmid, free, and prophage which means that phage genome is integrated into the bacterial chromosome. Based on the results of this study, the cell density of P. freudenreichii JS7 strain increases faster in anaerobic oxygen concentration comparing to aerobic and two staged oxygen concentrations. Based on the results of the bioreactor study, the bacterium can anaerobically form different size of colonies for the cell plating. The bacteriophage genome may be present as a plasmid, free and integrated into the bacterial chromosome. The results of the bacteriophage study might give signs that P. freudenreichii JS7 could be able to utilize the lysogenic life cycle in anaerobic growth condition.