Glucose amendments are associated with structural and hormonal shifts in a Fungal-Algal-Bacterial (FAB) consortium

Abstract The fungal-algal-bacterial (FAB) consortium composed of Euglena mutabilis, Talaromyces, and Acidiphilium acidophilum is a natural acid-tolerant assemblage whose heavy metal handling may depend on interspecies cooperation rather than a single-organism uptake alone. Here, glucose was used as a simplified laboratory model of labile carbon availability to test whether carbon input reorganizes consortium structure and stress responses under CdCl2 exposure. Glucose supplementation promoted fungal hyphal development, more extensive visible bacterial colonization, pronounced flocculation, and higher Euglena cell densities under CdCl2 stress. CdCl2 accumulation relative to Euglena cell abundance increased over time in all CdCl2-treated cultures but did not differ significantly among glucose treatments. Hormone profiling revealed distinct extracellular responses under glucose + CdCl2, including elevated bioactive trans-Zeatin (tZ), gibberellin GA7, methyl-thiolated cytokinins (CKs), and jasmonic acid (JA), consistent with coordinated consortium-level signalling under metal stress. Scanning electron microscopy (SEM) provided visual evidence of the FAB physically restructuring when grown in glucose, while transmission electron microscopy (TEM) identified previously uncharacterized electron-dense intravacuole bodies within E. mutabilis, although their identity could not be determined. Together, these findings show that glucose availability reorganizes structural and biochemical signalling of the FAB consortium and is associated with changes in consortium organization and physiological responses under heavy metal stress. They also highlight coordinated structural and biochemical responses associated with consortium persistence under acidic, metal-rich conditions and identify directions for future mechanistic investigations.