In the master's thesis we studied the interspecies interaction between the bacteria Bacillus subtilis and Streptomyces rimosus. We wanted to find the signaling molecule synthesized by bacteria B. subtilis, that triggers the pink substance synthesis in bacteria S. rimosus on the MSgM medium by using the spent medium of B. subtilis from different time points and different concentrations of FeCl3. We found out that signaling molecule synthesized by bacteria B. subtilis is part of the basal metabolism, it’s weight is less than 3 kDa, it is not a protein, probably not a siderophore and it is synthesized independently of the concentration of FeCl3 in the medium. We studied whether the cocultivation of both bacteria in the MSgM medium induced intracellular oxidation in at least one of the studied organisms and whether the level of intracellular oxidation influences the synthesis of pink substance produced by S. rimosus. The formation of pink substance was checked by cultivation of S. rimosus with mutants B. subtilis (katA or perR). We have examined the expression of the katA gene promoter in B. subtilis while adding the spent medium of S. rimosus. The level of intracellular oxidation was determined using H2DCFDA.We have found that the cultivation of bacteria B. subtilis and S. rimosus influences the level of intracellular oxidation and that the increased level of intracellular oxidation most likely does not affect the production of pink substance in S. rimosus.