A systematic approach to determine the outcome of the competition between two microbial species in bioreactor cocultures.

The two-species microbial cocultures are effective in terms of awakening the cryptic biosynthetic pathways. They may also lead to the improved production of previously discovered molecules. Importantly, only a few outcomes of the cocultures may prove desirable, namely those leading to the formation of useful secondary metabolites. To address this issue, a method allowing for the evaluation of the final outcome of the co-culture process and fine-tune the cocultivation strategy was proposed. The systematic approach was supported by the experimental data from the bioreactor runs with the participation of Aspergillus terreus and Penicillium rubens confronted with Streptomyces rimosus and Streptomyces noursei. Kinetic, morphological and metabolic aspects of dominance were analysed via the newly proposed formula describing the dominance pattern. The suggested method involved the determination of the numerical value representing the dominance level. When it was high (value 1) no useful metabolites were formed apart from those originating from the winning counterpart. But either for the partial dominances or when the winning organism changed within the run or when the competition ended in draw, the number of the secondary metabolites of interest in the broth was the highest. Next, the systematic approach illustrated how the delayed inoculation strategy influenced the level of dominance leading to the change of winning counterpart and the set of metabolites produced. The proposed systematic approach allows for the reliable determination of the level of dominance in the two-species cocultures to seek for the potentially useful substances for future applications.