The dynamic roles of intracellular vacuoles in heavy metal detoxification by Rhodotorula mucilaginosa.

Aims: Rhodotorula mucilaginosa (Rho) can develop a range of strategies to resist the toxicity of heavy metals. This study aimed to investigate the physiological responses and transcriptomic regulation of the fungus under different heavy metal stresses.

Methods and results: This study applied transmission electron microscopy and RNA-seq to investigate the fungal resistance to Pb, Cd, and Cu stresses. Under Pb stress, the activated autophagy-related genes, vesicle-fusing ATPase, and vacuolar ATP synthase improved vacuolar sequestration. This offsets the loss of lipids. However, the metal sequestration by vacuoles was not improved under Cd stress. Vacuolar fusion was also inhibited following the interference of intravacuolar Ca2+ due to their similar ionic radii. Cu2+ showed the maximum toxic effects due to its lowest cellular sorption (as low as 7%) with respect to Pb2+ and Cd2+, although the efflux pumps and divalent metal ion transporters partially contributed to the detoxification.

Conclusions: Divalent cation transporters and vacuolar sequestration are the critical strategies for Rho to resist Pb stress. Superoxide dismutase (SOD) is the main strategy for Cd resistance in Rho. The intracellular Cu level was decreased by efflux pump and divalent metal ion transporters.