Study on intracellular detoxification mechanisms of Aspergillus sydowii under cadmium stress

Soil cadmium (Cd) contamination poses significant ecological and health risks because of its persistence and bioaccumulation. This study elucidated the intracellular detoxification mechanisms of Aspergillus sydowii, a Cd-resistant fungus isolated from contaminated soil, with a specific focus on the roles of the isolated protoplasts and vacuoles. Through subcellular fractionation, specific fluorescent probe analysis, and enzymatic assays, we quantified Cd distribution, chelation detoxification, and oxidative stress responses. The results revealed that 55.3-64.1 % of cellular Cd was stored in the cell wall, whereas vacuoles accounted for 22.1-28.9 %. Bound Cd was the predominant form, reaching 85.9 % in protoplasts and 83.1 % in vacuoles. Under low-to-medium Cd concentrations, chelators primarily localized in vacuoles to chelate abundant Cd therein. In contrast, high Cd stress triggered cellular allocation of limited chelator resources to protect vital organelles in the cytoplasm, with macromolecular chelators exhibiting relatively stronger protective effects. Although reactive oxygen species (ROS) levels increased by 3.5-fold, extravacuolar compartments displayed comparatively elevated glutathione/oxidized glutathione and acetylsalicylic acid/docosahexaenoic acid ratios versus vacuolar compartments, evidencing that vacuoles function not merely as heavy metal sequestration hubs but also as pivotal regulators in alleviating oxidative stress. These findings delineate vacuolar compartmentalization and chelation detoxification as co-essential mechanisms, providing critical insights for optimizing fungal-based bioremediation technologies.