Zinc concentrations effect on S. cerevisiae growth rate and its zinc absorption
The effect of zinc concentrations on the yield of yeast biomass and the biosorption of zinc by yeast cells of S. cerevisiae strain was evaluated. The effects of supplementing the SDB culture medium with ZnSO4 on the yeast growth rate were examined at 24-hour intervals (0, 24, 48, and 72 h) and the results were assayed using spectroscopic methods. The highest growth rate at 24 hours after inoculation in the presence of 25 µg/ml of zinc concentration (OD600 = 2.520 µg/ml), was observed. Actually, the growth rate of S. cerevisiae in culture medium gradually increased correspondingly with the incubation time (0-24 h) and 25 µg/ml of zinc concentration and leveled off at 24 h after inoculation (figure 2). Dry matter content of yeast biomass also illustrated the maximum weight 24 h after inoculation in the presence of 25 µg/ml of zinc concentration (0.206g of dry yeast biomass /200 ml SDB medium), verifying the optical density result of this group. Also, the maximum uptake of zinc by yeast cells was observed using AAS method at 24 h after inoculation; suggesting that, the increment of incubation time after 24 h, did not positively affect biosorption (table 1).
Table 1. Effect of zinc concentrations on the yield of dry yeast biomass and zinc uptake by S. cerevisiae