In the master's thesis, we investigated the relationship between dissolved oxygen, surfactin operon expression, and optical density in shaken cultures of Bacillus subtilis. We have successfully assembled a device for simultaneous cultivation, sampling, and monitoring of dissolved oxygen. Surfactin operon expression was indirectly monitored using the srfA-lacZ genetic construct. The results show that dissolved oxygen generally decreases with increasing cell density; however, at the end of the exponential growth phase, fluctuations in dissolved oxygen concentration occur, followed by fluctuations in surfactin operon expression. The increased extracellular β-galactosidase concentrations, oxygen availability, and altered oxygen concentration fluctuations in mutants deficient in ΔlytABC, genes encoding enzymes responsible for autolysis, suggest that cell lysis is involved in local oxygen concentration fluctuations. Overall, during growth, the expression of the surfactin operon is positively correlated with cell density and negatively correlated with dissolved oxygen. In shaken cultures, the relationship between cell density and dissolved oxygen is generally in a negatively linearly related.
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