Bacillus subtilis lives in an environment with frequent osmotic changes. In this master's thesis we aimed to investigate the influence of the DegQ-controlled DegS-DegU system and ComQXPA system, involved in cell density or quorum sensing, on the adaptation of B. subtilis to high salinity. Strains included were PS-216 wild-type (wt) strain, mutant strain PS-216 ΔcomQ without production of an active signal ComX of the ComQXPA system, and mutant strain PS-216 ΔdegQ without DegQ production. Growth and morphological properties of colonies in liquid and solid SM and MSgg media with different NaCl concentrations were determined. In addition, the expression of fluorescently labelled proH, epsA, and srfAA gene promoters was monitored at different salt levels in MSgg liquid medium. Similar areas of the colonies of the mutant ΔcomQ at all salinities and faster beginning of the proH gene promoter expression at increased salinity in comparison to the wt strain show more efficient mechanism of adaptation of the mutant ΔcomQ strain to high salinity. Expression of the epsA gene promoter was higher in the ΔcomQ mutant than in the wt strain, indicating better biofilm formation. The lower activity of the DegS-DegU system in the ΔdegQ mutant affects colony morphology, while the dynamics of colony formation and their final size are similar to those of the wt strain. The promoters of proH and epsA genes are expressed later and less intensely, indicating poorer adaptation to increased salinity and inhibited biofilm formation. The highest expression of srfAA gene promoter was in the ΔdegQ mutant, followed by the wt and ΔcomQ mutant. From the results obtained, we can conclude that the absence of the ComQXPA system accelerates the adaptation of the ΔcomQ mutant to increased salinity, while the lower activity of the DegS-DegU system slows down the adaptation of the ΔdegQ mutant to increased salinity.
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