Mutually beneficial FAB consortia fortify stress resistance of Euglena mutabilis: evidence from sequencing, antibiotics, and Cd challenges

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Abstract Background Synthetic algal-fungal and algal-bacterial cultures have been investigated for technological applications because the microbe interactions enhance growth and improve stress tolerance of the co-cultures. Yet these studies often disregarded natural consortia due to the complexity of environmental samples. The protist Euglena mutabilis is found in association with other microbes in acidic environments with high heavy metal (HM) concentrations. This may suggest that microbial interactions are essential for the alga’s ability to tolerate these extreme environments. Our study assessed the Cd tolerance of a natural fungal-algal-bacterial (FAB) association where the algae is replaced by the photosynthetic protist E. mutabilis. Results This study provides the first assessment of antimycotic and antibiotic agents on E. mutabilis. Our results indicate that suppression of associated fungal and bacterial partners significantly decreases the number of viable E. mutabilis cells upon Cd exposure. However, axenic Euglena gracilis recovered and grew well following antibiotic treatments. Interestingly, both Euglena species displayed increased chlorophyll production upon Cd exposure. Finally, the constituent organisms in the E. mutabilis FAB consortia were identified using PacBio sequencing to be a Talaromyces sp and Acidiphilium acidophilum. Conclusion This study uncovers a possible tripartite symbiotic relationship, a FAB consortia, that withstands exposure to high concentrations of HM. This unique fungus, bacterium, and E. mutabilis interaction strengthens the photobiont’s resistance to Cd and provides a model for the types of FAB interactions that could be used to create a self-sustaining bioremediation technology.

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