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Background Microbial co-cultures are of great interest in biotechnology in quest to mimic competition and interaction within the natural environment. Thereby, the production of novel natural products can be stimulated. Especially filamentous organisms offer a huge metabolic diversity. However, most studies in this direction empirically combine different organisms without a deep understanding of the underlying interactions and population dynamics. Results Here, we apply high-throughput online monitoring of the respiration rate and fluorescence of tagged strains to provide detailed insight into co-culture interactions. A model synthetic filamentous co-culture of the cellulolytic fungus Trichoderma reesei RUT-C30 and the non-cellulolytic bacterium Streptomyces coelicolor A3(2) was developed. The aforementioned co-culture was set-up to use α-cellulose as carbon source. This established a dependency of S. coelicolor on T. reesei, which secretes cellulases that in turn provide cellulose hydrolysate sugars to S. coelicolor. For this process, the respiration rate allowed to assess the degree of cellulose consumption and thereby, clearly differentiate between conditions of successful and non-successful cellulase formation. Furthermore, T. reesei and S. coelicolor were tagged with mCherry and mNeonGreen fluorescence proteins, respectively. Hence, the individual contributions of the strains in this co-culture system could be dissected, which provided detailed information on the population dynamics. As tunable biotic parameter, the inoculation ratio was tested. Both partners were observed to outcompete the other when given a too high inoculation advantage. However, adequate inoculation ratios for a co-culture with successful cellulase production and simultaneous growth of both partners were found. In these co-cultivations, production of pigments could be triggered, which was not observed in respective axenic control cultures. Finally, population dynamics were also tuned in co-cultures by modulation of abiotic factors, osmolality and shaking frequency. Increased osmolality provided a growth advantage to S. coelicolor and delay of T. reesei growth and cellulase production. In contrast, an increase of shaking frequency had a drastic negative effect on S. coelicolor biomass formation. Conclusion This work presents how information gaps for complex co-cultures can be comprehensively resolved by detailed online insight. The information gathered with respiration rate and fluorescence monitoring allows for set-up of tailor-made co-culture bioprocesses. |
