Kaszecki, Emma

Acid mine drainage (AMD) and metal-contaminated tailings represent some of the most inhospitable aquatic environments on Earth, characterized by low pH, elevated metal concentrations, and chronic carbon limitation. Yet these systems support microbial consortia with remarkable resilience. Among the most conspicuous inhabitants is Euglena mutabilis, an acidophilic protist traditionally regarded as an indicator species of AMD but seldom thoroughly investigated. This thesis reframes E. mutabilis at the center of a fungal-algal-bacterial (FAB) consortium, demonstrating that its cadmium tolerance and persistence are emergent properties of the consortium.

Culture-based experiments revealed that E. mutabilis survival under cadmium stress declined when fungal and bacterial partners were disrupted, underscoring their indispensability. Glucose supplementation revealed the consortium's capacity for structural and metabolic reorganization: fungal hyphae bound algal cells into flocs, bacterial associates proliferated, and hormone production shifted. Hormone profiling suggested a distributed signaling system in which fungi contributed cytokinins (CKs) and gibberellins while algae produced methyl-thiolated CKs, jasmonic acid, and salicylic acid. Transmission electron microscopy revealed bacterial-like inclusions within algal vacuoles, suggesting facultative endosymbiosis or phagotrophic retention. Transcriptomic analyses revealed that cadmium stress suppresses light-harvesting complexes and growth-promoting hormone biosynthesis while activating metal transporters and chloroplast sequestration mechanisms.

Beyond stress physiology, the FAB consortium unlocked chemical diversity inaccessible to axenic cultures. Molecular networking revealed that environmental consortia consistently produced unique metabolite families, often linked to silent biosynthetic pathways. Metagenomic sequencing linked these products to bacterial gene clusters further supporting the view that metabolic innovation is an emergent property of the collective.

Together, these findings suggest that the FAB consortium should be understood not as a loose association but as a microbial superorganism. This framing extends beyond the holobiont concept by dissolving the hierarchy between host and symbiont: E. mutabilis, fungi, and bacteria are all indispensable, and the identity of the host itself becomes blurred.

By reframing E. mutabilis as the nucleus of a microbial superorganism, this work highlights both theoretical and applied significance. It advances ecological understanding of how life persists under geochemical extremes, while pointing to new opportunities for sustainable bioremediation and natural product discovery through the deliberate cultivation of naturally evolved microbial consortia.

Author Keywords: Algal symbiosis, Bioremediation, Co-culture, Hormones, Microscopy, Transcrioptomics