In the master's thesis we wanted to optimize the conditions of cocultivation of cultures of bacterial species S. rimosus and B. subtilis. We cocultivated bacteria in various solid and liquid growth media and monitored their growth and morphology. We used a wild type of B. subtilis and 3 different strains of S. rimosus bacteria, that produce different amounts of antibiotic oxytetracycline. The most noticeable influence on morphology of one bacterial species on another was observed on MSgg and MSgM media. On these media S. rimosus cocultured with B. subtilis secreted an unknown pink pigmented compound. The bacterium S. rimosus secreted the pigmented compound in both liquid and solid MSgg/MsgM media in the presence of various mutants of B. subtilis and in the presence of the B. subtilis conditioned medium. S. rimosus also secreted the pink compound in the presence of bacterial species B. subtilis, B. licheniformis, B. megaterium, E. coli and S. marcescens. We examined the effect of FeCl3 concentration on the secretion of the pigmented compound and found pigmentation to occur at concentrations above 25 µM FeCl3 and that the pigmentation intensity increased up to 125 µM FeCl3, when it reached the plateau. The pigmentation appeared only when the bacteria were grown in coculture, but not in the absence of FeCl3 and in S. rimosus monoculture. We investigated the influence of the media pH on pigmentation and no correlation was observed, except that in MSgM medium with 50 µM FeCl3 and pH 7 no pigmentation was observed. We also stuided effect of cocultivation on the expression of the surfactin promoter and exopolysaccharides (EPS) promoter in B. subtilis in the presence of 5% conditioned medium of S. rimosus R7. The expression of the surfactin promoter was lower in the presence of conditioned medium. Therefore, we conclude that S. rimosus secretes an unknown compound, that inhibits the activitiy of the surfactin promoter in B. subtilis. We did not notice the effect on the expression of EPS promoter.
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