Bacillus subtilis synthesizes several secondary metabolites, one of which is also bacillaene. The synthesis of some secondary metabolites is regulated by the quorum sensing system (QS). In order to check whether bacillaene synthesis is also regulated by QS, we prepared strains with defects in the QS system and a reporter fusion of the PpksC promoter with yfp. The methods included monitoring fluorescence intensity with a fluorescence microplate reader at the level of the whole population, and with a confocal fluorescence microscope (CLSM) at the level of a single cell. Microscopy offers us an insight into the single-cell level; therefore, these two methods gave us different results. It can be confirmed that the bacillaene expression is affected by the QS system in PS-216, which on the other hand cannot be confirmed for the NCIB3610. Strains PS-216 and NCIB3610 differ in the expression of genes required for bacillaene synthesis, which can be confirmed at the single cell level and at the level of the whole population. Using the CLSM method, we found that two populations occur in all strains - the first - more numerous with a lower level of bacillaene synthesis, and the second - less numerous with a higher level of bacillaene synthesis. In addition, we observed differences in bacillaene expression during growth at different time points. There are minimal differences in the expression of genes required for bacillaene synthesis between wild-type PS-216 and QS-defective strains, while there are no statistically significant differences between NCIB3610 strains. The results with the CLSM method were not reproducible, so the hypotheses could be tested in the future with other independent methods (for example, flow cytometry), which would confirm or refute the proposed hypotheses with greater certainty.
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