The production of secondary metabolites by microorganisms depends on many factors. Therefore, it is crucial to establish the main conditions of microbial growth to obtain products with biotechnological potential. The aim of the research was to determine the optimal culture conditions of the Rhodococcus opacus FCL1069 strain producing an exopolymer with flocculating properties. Different carbon (e.g. glucose, lactose) and nitrogen (e.g. yeast extract, peptone) sources were used for optimization of bacterial growth. Moreover, the impact of addition of ions to the culture broth was established. During bacterial growth, the protein content was determined with the Bradford method and flocculating activity was tested using a kaolin and calcium chloride mixture. The total sugar concentration in the culture broths on the subsequent days of cultivation was measured with the Dubois method. The investigations presented in this study allowed obtaining an exopolymer with the highest possible flocculating activity in the shortest incubation time.

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