Hyperaccumulation of zinc by zinc-depleted Candida utilis grown in chemostat culture

Abstract

The steady-state levels of zinc in Candida utilis yeast grown in continuous culture under conditions of zinc limitations are <1nmol Zn2+/mg dry weight of cells. Unlike carbon-limited cells, zinc-depleted cells from a zinc-limited chemostat possess the capacity to accumulate and store zinc at levels far in excess of the steady-state level of 4 nmol/mg dry biomass observed in carbon-limited chemostat cultures. Zinc uptake is energy-dependent and apparently undirectional since accumulated 65Zn neither exists from preloaded cells nor exchanges with cold Zn2+. The transport system exhibits a high affinity for Zn2+ (Km =.36micrM) with a Vmaxof 2.2 nmol per minute per milligram dry weight of cells. Growth during the period of the uptake assay is responsible for the apparent plateau level of 35 nmol Zn2+/mg dry weight of cells achieved after 20-30 min in the presence of 65Zn at pH 4.5 and 30 degrees C. Inhibition of growth during the uptake assay by cycloheximide results in a biphasic linear pattern of zinc accumulation where the cellular zinc is about 60 nmol/mg dry weight after 1 h. The enhanced level of accumulated zinc is not inhibtory to growth. Zinc-depleted C. utilis contains elevated amounts of polyphosphate and this anionic evidence does not allow discrimination between possible regulation of zinc homestasis either by inhibitions of zinc efflux through control of the membrane carrier or by control of the synthesis of a cytoplasmic zinc-sequestering macromolecule.

Uptake of Zn2+ by yeast and mycelial growth form of Aureobasidium pullulans grown in chemostat culture

“…The cell density was kept low in the experiments and with the lowest initial external Zn P concentration (0.2 WM) the decrease in the external Zn P was less than 20% during the ¢rst 2 min. A continuous decrease in the rate of Zn P uptake has been demonstrated previously for Candida utilis [7], Neocosmospora vasinfecta [11] and C. albicans [12].…”

“…Yeast cells harvested from zinclimited cultures had a lower half saturation constant (K m ) and a higher maximal rate of transport (V mx ) than yeast cells growing in medium with su¤cient zinc (Table 1). An enhanced ability to accumulate Zn P by cells de¢cient in zinc as compared to cells grown with su¤cient zinc has been shown for C. utilis [8,7] and for Aspergillus parasiticus [14]. Thus, it has been interpreted as a general phenomenon in both yeast and ¢lamentous fungi that the high a¤n-ity zinc uptake system is regulated by the zinc content of the cells [6].…”

Zinc Uptake and Toxicity in the Yeasts Sporobolomyces roseus and Saccharomyces cerevisiae

“…Neocosmospora vasinfecta and Candida albicans could grow in zinc concentrations of up to 0.1 and 0.3 mM, respectively (Paton & Budd, 1972;Ross, 1982), while Candida utilis accumulated high levels of intracellular zinc [up to 122 nmol ZnZ + (mg dry wt)-J without any reduction of growth rate or viability (Failla & Weinberg, 1977;Lawford et al, 1980). Cation uptake by yeasts is typically biphasic, involving rapid, metabolism-independent binding to cell surfaces, followed by a slower phase of metabolism-dependent intracellular uptake (Rothstein et al, 1958;Rothstein, 1959;Passow & Rothstein, 1960;Fuhrmann & Rothstein, 1968;Ponta & Broda, 1970;Norris & Kelly, 1977;Failla et al, 1976;Failla & Weinberg, 1977;Gadd & Mowll, 1983).…”

Accumulation of zinc and cadmium by Cytophaga johnsonae

“…This was proposed to be due to deficiency of energy for the energy-driven metal uptake systems. However, other investigators (Failla & Weinberg 1977, Lawford et al 1980 found that the yeast Candida utilis accumulated high intracellular levels of zinc without any reduction of viability, which may have been due to the presence of detoxification mechanisms such as internal compartmentalization or binding to metal-sequestering macromolecules.…”

“…This was the case for zinc accumulation in yeasts and fungi (Paton & Budd 1972, Failla et al 1976, Failla & Weinberg 1977, Lawford et al 1980, Mowll & Gadd 1983, and in Escherichia colt (Bucheder & Broda 1974). Metals with no known biological function should not readily enter the cell unless specific transport pathways are present (Hughes & Poole 1986).…”