Temperate phage SPβ regulates the expression of the spsM gene in Bacillus subtilis through precisely controlled integration and excision. The spsM gene is involved in the formation of the spore crust and contributes to the dispersibility of spores in aquatic environments. Excision of the SPβ prophage from the spsM gene occurs exclusively in the spore mother cell and involves the sprB gene product, whose expression is associated with the sporulation program. Previous studies have shown that excision of the SPβ prophage is closely linked to the sporulation process in the bacterium Bacillus subtilis. Since sporulation dynamics differ between Bacillus subtilis strains and growth media, we investigated the dynamics of prophage excision in different Bacillus subtilis strains under different cultivation conditions. In this master's thesis we found that excision of the prophage in the laboratory strain 168 was delayed in LB medium compared with the natural isolate, whereas no such differences in the dynamics of prophage excision between the two strains were observed in the sporulation medium NSM. A similar pattern was observed in sporulation dynamics. The initiation of sporulation in LB medium was delayed in the laboratory strain, whereas in NSM medium the dynamics were more synchronised between strains. These results suggest that the composition of the growth medium plays an important role in determining sporulation timing. We found that mutationally preventing SPβ prophage excision does not directly affect the timing of sporulation initiation. Our results indicate that SPβ prophage excision and sporulation are developmentally coordinated processes that are strongly influenced by the genetic background of the host and environmental conditions. This study contributes to a better understanding of the role of temperate phages in the regulation of bacterial developmental processes.
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