In Pb 2+ accumulation by Aureobasidium pullulans, the time to reach an equilibrium state was not dependent on the initial cell dry weight. The Pb 2+ accumulation capacity was increased from 56.9 to 215.6 mg Pb 2+ /g cell dry weight as the biomass was stored from 1 to 53 days, and correlated with the amount of excreted extracellular polymeric substances (EPS). It was observed that Pb 2+ accumulated only on the surface of the intact cells of A. pullulans due to the existence of EPS, whereas Pb 2+ penetrated into the inner cellular parts of the EPS-extracted cells. IntroductionThe presence of heavy metal ions in municipal wastewater may have detrimental effects on the water puri®cation systems. In the interest of public health protection studies concerning the sources of heavy metal ions, their removal mechanisms in wastewater treatment plants, and the fate of heavy metal ions discharged into surface streams and/or land are deemed necessary. In recent years, the investigation of bioaccumulation/biosorption for the removal of heavy metal ions by microorganisms and their microbial products has been increased [1±3]. Microorganisms bind metal ions via any one (or more) of several known mechanisms, including adsorption, inorganic precipitation, complexation, ion exchange and active transport [4].In particular, Pb 2+ , well recognized for its detrimental effect on the environment where it accumulates throughout the food web, is generated from mining, metal, dyestuff, electric, and petroleum industries, etc. It is well known that Pb 2+ is easily accumulated in microorganisms.For instance, equilibrium metal uptake values using freeze-dried Rhizopus arrhizus increased in the order: Sr 2+ < Mn 2+ < Zn 2+ < Cd 2+ < Cu 2+ < Pb 2+ , and were positively correlated with the covalent index of the metal ions [5]. The work of Leusch et al. [6] indicated that the order of adsorption for metal ions in the biomass particles of Sargassum¯uitans was Pb 2+ > Cd 2+ > Cu 2+ > Ni 2+ > Zn 2+ . It has also been described that fungal biomass is capable of sequestering and accumulating heavy metal ions [7,8]. Fungal pigments are implicated in metal resistance and/or uptake by some fungal cultures. Biosynthesis of metalbinding pigment melanin, produced as a response to copper-induced culture stress, has been studied in a polymorphic fungus Aureobasidium pullulans [9]. Nevertheless, the relationship between the process of heavy metal ion uptake and extracellular polymeric substances (EPS) in fungi has not been fully understood.In the present study, in an attempt to elucidate the detailed process of Pb 2+ accumulation in A. pullulans, the critical effect of EPS was investigated using transmission electron microscope (TEM). Materials and methods Microorganism and growth conditionAureobasidium pullulans KFCC (Korean Foundation of Culture Collection) 110245 was aerobically cultivated with 100 ml medium containing (as g/l) 200, sucrose; 20, yeast extract; 5, K 2 HPO 4 ; 2, MgSO 4 á 7H 2 O; 15, NaNO 3 in a rotary-shaker incubator (150 rpm) at 30°C for 72...
Pb 2+ accumulation in Saccharomyces cerevisiae changed by Hg 2+ and cell conditions. The accumulated Pb 2+ amounts decreased from 0.22 to 0.02 mmol Pb 2+ /g cell dry weight by the existence of Hg 2+ . But the total metals accumulation (0.42 mmol metal ions/g cell dry weight) was not changed. The order of accumulated Pb 2+ amounts (mg Pb 2+ /g cell dry weight) according to the cell conditions at an equilibrium state was shown as the original cell (260) > 5 times autoclaved cell for 15 min (150) > grinded cell after drying (100) > autoclaved cell for 5 min (30). IntroductionAs a result of many industrial and waste disposal operations, our environment is becoming more and more contaminated by heavy metal ions. Traditional technologies for the removal of heavy metals, such as chemical reduction and precipitation or ion exchange, are often ineffective and/or very expensive when used for the removal of heavy metal ions to very low concentrations. Moreover, these methods are speci®c to each metal ion [1]. Biological method offers a potential alternative to existing methods and is de®ned as the accumulation and concentration of pollutants from aqueous solutions by the use of biological materials. Amongst the heavy metal ions, Pb 2+ is hazardous to the various ecosystems and to human health [2]. Pb 2+ has been used as an industrial raw material for storage battery manufacture, printing, pigments, fuels, photographic materials, and matches and explosive manufacturing. Emissions of Pb 2+ into the air, water, and soil from human sources are at least 30 times greater than those from natural sources. Once Pb 2+ enters the blood only about 10% are excreted; the rest is stored in the bones for decades. Young children, infants, and unborn fetuses are especially susceptible to harm from even very low levels of Pb 2+ in their blood [3].Also, Pb 2+ has been known to easily accumulate on microorganisms as follows. Equilibrium metal uptake values using freeze-dried fungi Rhizopus arrhizus increased in the order: Sr 2+ < Mn 2+ < Zn 2+ < Cd 2+ < Cu 2+ < Pb 2+ , and were positively correlated with the covalent index of the metal ions [4]. The order of adsorption for algae Sargassum¯uitans was Pb 2+ > Cd 2+ > Cu 2+ > Ni 2+ > Zn 2+ [5].Although the biological method has many advantages compared to the conventional treatment methods [6], the biological materials have several limitations on the aspects of application compared to the conventional methods. Especially, waste yeast biomass represents a good source of biological method because it is cheap, easily recovered at the end of fermentation and produced in large quantities. However, before use, the factors affecting metal uptake by the biomass must be de®ned. These factors include metal concentration in solution, biomass concentration, solution pH, temperature, the presence of competing ions and the metabolic state of the microorganism. This paper describes the characteristics of Pb 2+ accumulation by Saccharomyces cerevisiae according to the presence of competing ion such as Hg 2+ and t...
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