Comparison of the Rhodotorula mucilaginosa Biofilm and Planktonic Culture on Heavy Metal Susceptibility and Removal Potential

This study compares the effect of heavy metals (Hg2+, Cu2+, and Pb2+) on the Rhodotorula mucilaginosa and Saccharomyces boulardii biofilm and planktonic cells. A MBEC (TM)-HTP assay was used to test the levels of tolerance to heavy metals. The minimum inhibitory concentration (MICp) and minimum lethal concentration (MLCp) of the R. mucilaginosa and S. boulardii planktonic cells were determined, as well as minimum biofilm eradication concentration (MBEC). Metal removal efficiency was determined by batch biosorption assay. Previous studies had focused on heavy metal tolerance and removal efficiency of planktonic cells from Rhodotorula species only. Hence, our study presents and compares results for metal tolerance and removal efficiency of the R. mucilaginosa planktonic cells and biofilm. Biofilm tolerance was higher than the planktonic cells. The R. mucilaginosa planktonic cells showed the tolerance in the presence of Hg2+ (MICp 0.08 mM), Cu2+ (MICp 6.40 mM), and Pb2+ (MICp 3.51 mM), while the S. boulardii planktonic cells only tolerated Pb2+ (MICp 0.43 mM). The R. mucilaginosa biofilm showed the highest tolerance in the presence of Hg2+ (MBEC >0.31 mM), Cu2+(MBEC >12.81 mM), Pb2+ (MBEC >7.12 mM), and obtained results were confirmed by fluorescence microscopy. S. boulardii did not show potential in biofilm formation. The R. mucilaginosa biofilm exhibited better efficiency in removal of all tested metals than the planktonic cells. Metal removal efficiency was in the range from 4.79-10.25% for planktonic cells and 91.71-95.39% for biofilm.