Contrasting the dynamic changes of carotenoid accumulation in Rhodotorula mucilaginosa under Pb and Cd stress.

Carotenoids are synthesized to compete with ROS (reactive oxygen species) accumulation under HM stress. This study contrasted the dynamic responses of Rhodotorula mucilaginosa (Rho) under either Pb(Ⅱ) or Cd(Ⅱ) stress. Carotenoid accumulation was observed in all the treatments (except at 2500 mg/L) under Pb(Ⅱ) stress. In particular, Rho exhibited the most intense carotenoid accumulation at 200 mg/L Pb(Ⅱ) level. In addition, Pb(Ⅱ) cations were inclined to form Pb-rich deposits intra- and extracellularly, which weakened their toxicity. In contrast, carotenoid accumulation in Rho was relatively weak at Cd(Ⅱ) level of >100 mg/L due to its high toxicity. The carotenoid accumulation was only evident at 25 mg/L Cd(Ⅱ) level. Under Cd(Ⅱ) stress, the abundances of antioxidants (SOD and GSH) were peaked after 72 h incubation. In addition, the signal of tyrosine in 3D-EEM analysis was also peaked at 72 h. Meanwhile, the critical role of key genes involved in carotenoid metabolic process (HMGCs, mvaK2, mvaD, and GGPS1) were upregulated. Therefore, carotenoids would substantially contribute to the detoxification under strong Cd(Ⅱ) stress after 72 h incubation.