Hg tolerance and biouptake of an isolated pigmentation yeast Rhodotorula mucilaginosa

A pigmented yeast R1 with strong tolerance to Hg(2+) was isolated. Phylogenetic identification based on the analysis of 26S rDNA and ITS revealed R1 is a Rhodotorula mucilaginosa species. R1 was able to grow in the presence of 80 mg/L Hg(2+), but the lag phase was much prolonged compared to its growth in the absence of Hg(2+). The maximum Hg(2+) binding capacity of R1 was 69.9 mg/g, and dead cells could bind 15% more Hg(2+) than living cells. Presence of organic substances drastically reduced bioavailability of Hg(2+) and subsequently decreased Hg(2+) removal ratio from aqueous solution, but this adverse effect could be remarkably alleviated by the simultaneous process of cell propagation and Hg(2+) biouptake with actively growing R1. Furthermore, among the functional groups involved in Hg(2+) binding, carboxyl group contributed the most, followed by amino & hydroxyl group and phosphate group. XPS analysis disclosed the mercury species bound on yeast cells was HgCl(2) rather than HgO or Hg(0).