Tyrosols retrieved from traditionally brewed yeasts assist in tolerance against heavy metals and promote the growth of cells.

Heavy metals act as cofactors for several microbial enzymes and are required in low concentrations for the proper biological functioning of yeasts. Because concentrations beyond the permitted threshold can damage a cell's functionality and viability, metal tolerance in yeasts towards such heavy metals is therefore desirable during fermentation. Tyrosol, a quorum-sensing molecule in yeasts, protects yeasts from oxidative stress induced by various factors, but the performance of the molecule under heavy metal-induced stress is not known. In this investigation, the metal tolerance of four species of endemic yeasts from northeast India, Wickerhamomyces anomalus, Candida tropicalis, Saccharomyces cerevisiae and Candida glabrata, isolated from traditional starter culture cakes, was tested towards zinc (Zn+2), manganese (Mn+2), cobalt (Co+2) and copper (Cu+2) in the presence and absence of tyrosols retrieved from these isolates. The decreasing order of the tolerance of isolates was found to be Mn+2 > Zn+2 > Co+2 > Cu+2. Under the influence of tyrosols, isolates showed enhanced growth at their upper metal tolerance limit. Candida tropicalis showed enhanced growth (2-48-fold, P < 0.0001) in all the tested metal consisting medium (2 mM Zn+2, 5 mM Mn+2, 2 mM Co+2 and 1 mM Cu+2), while W. anomalus, C. glabrata and S. cerevisiae showed increased growth (3-17-fold, P < 0.0001) in Zn+2 (2 mM), Mn+2 (5 mM) and Cu+2 (1 mM) augmented medium. The overall result suggests that tyrosol exerts a protective effect under heavy metal-induced stress, which could be useful in enhancing the quality of fermented products.