Oxidative stress response of native yeasts to heavy metals

Abstract

A possible consequence of heavy metal exposure is an increased production of reactive oxygen species (ROS) that could induce or exacerbate intracellular oxidative stress and can cause physiological stress. Defense mechanisms which counteract the impact of ROS, including enzyme and non-enzyme antioxidant systems, are found in all aerobic cells. In this work we study the antioxidant response of native yeasts to the oxidative stress produced by heavy metals. Yeast strains Meyerozyma guilliermondii 6N and Rhodotorula mucilaginosa 7Apo1 were cultured in YM media in absence/presence of K2Cr2O7 and CuSO4 alone or in metal mixtures. Cell-free extract was prepared and antioxidant enzymatic activities [catalase (CAT), superoxide dismutase (SOD) and thioredoxin reductase (TrxR)] were determined. The specific activity is given as U/mg protein. Total antioxidant capacity was determined by the modified ABTS* discoloration method [2,2'-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid)]. In both strains, the activity of SOD was higher in the presence of Cr (VI) showing significant differences with the control condition without the metal (p < 0.05, Tukey test), the CAT activity, in both strains the highest values were obtained with Cr (VI) and the mixture of metals but this activity was while this activity was reduced in the presence of Cu (II) and the mixture of metals. For lower in the presence of Cu (II). In the case of the TrxR activity, 7Apo1 and 6N did not show significant differences in the assayed conditions (p > 0.05, Tukey test). The total antioxidant capacity of 6N with Cr (VI) and Cu (II) was higher than the control while no differences were observed in the mixture of metals. 7 Apo1 did not show significant differences in the tested conditions (p > 0.05, Tukey test). Interaction between chemical elements, the level of oxidative stress and antioxidant defense play an important role in ecotoxicological response of microorganisms in polluted environments and our results provide additional confirmation for metal-mediated activation of the antioxidant enzymes in yeasts.