The Role of Carotenoid Pigments in Cr(VI) Tolerance, Biosorption and Bioaccumulation by <i>Rhodotorula mucilaginosa</i> UCM Y-1776 and its Mutants

Abstract

To compare Cr (VI) tolerance, biosorption and bioaccumulation for initial carotenoidsproducing yeast Rhodotorula mucilaginosa UCM Y-1776 and its mutants, twenty stable mutants with various intensity of colors were obtained using nitrosoguanidine (NSG). The ultraviolet was found to be inefficient as a mutagen in our study. Light- and non-pigmented mutants (4L and 2) demonstrated a significant growth inhibition by 30 mg/l Cr (VI) whereas wild strain was able to grow at much higher chromium concentrations (500 mg/l). Cr (VI) sorption ability of R. mucilaginosa UCM Y-1776 was higher than those of mutants. Cr (VI) sorption/uptake parameters (Qmax, b) were found to be close for initial pink-pigmented R. mucilaginosa UCM Y-1776 (Qmax = 950 5M/g), and its light-pigmented mutant 4L (Qmax = 678 5M/g) and non-pigmented mutant 2 (Qmax = 790 5M/g) by non-living biomass. Non-pigmented “white” mutant 2 showed the highest ability to sorb chromium ions by living biomass (Qmax = 1020 mmol/g). The least chromiumtolerant light-pigmented (mutant 4L) and non-pigmented yeasts showed the highest chromium uptake for living biomass. The results showed that the presence of carotenoids did not affect Cr (VI) ions sorption by yeast biomass which could highlight significance of chitin and glucan-mannoprotein complex in chromium biosorption. However pigment absence increased Cr (VI) bioaccumulation by living yeast demonstrating the protective role of carotenoids against hexavalent chromium toxicity.