Jung Ho Suh

Cation (K+, Mg2+, Ca2+) exchange in Pb2+ accumulation by Saccharomyces cerevisiae

Abstract The relationship between Pb2+ accumulation and cation (K+, Mg2+, Ca2+) release in Saccharomyces cerevisiae was extensively investigated. As Pb2+ accumulation proceeded, the release of cellular metal ions such as K+, Mg2+ and Ca2+ was concomitantly released within 24 h, thereafter Pb2+ penetrated into the inner cellular parts and consequently plasmolysis of the cell was observed by TEM analysis. Pb2+ accumulation process in S. cerevisiae after 24 h was metabolism-independent because of the absence of cell viability. As the cell storage time was prolonged, the released amount of K+ was markedly increased, while the amount of accumulated Pb2+ was nearly constant regardless of cell storage time and the time required to reach an equilibrium state was shortened. The autoclaved cells had less Pb2+ accumulation capacity than the untreated cells, and the amounts of released K+ and Mg2+ were very low due to the denaturation of cell surface and cell membrane.

A comparative study on Pb2+ accumulation between Saccharomyces cerevisiae and Aureobasidium pullulans by SEM (Scanning Electron Microscopy) and EDX (Energy Dispersive X-Ray) analyses

Scanning electron microscopy and energy dispersive X-ray analyses were carried out in a comparative investigation of Pb(2+) accumulation in Saccharomyces cerevisiae and Aureobasidium pullulans. In S. cerevisiae, the time required to reach an equilibrium state was shortened from 100 h to 1 h as the initial Pb(2+) concentration decreased from 96.5 mg/l to 16.0 mg/l, whereas the time was almost independent of initial Pb(2+) concentration in A. pullulans. Concomitant with the Pb(2+) accumulation, the cell surface of S. cerevisiae became rough and the amounts of potassium, phosphorus and sulfur on the cell surface decreased. However, significant increase of Pb(2+) on the cell surface after Pb(2+) accumulation was not observed due to Pb(2+) penetration into the cell interior. In contrast, the Pb(2+) accumulation had no significant effect on the surface characteristics of A. pullulans and extreme Pb(2+) accumulation was observed on the cell surface because Pb(2+) could not penetrate into the cell interior due to the existence of extracellular polymeric substances.

Inhibition effect of initial Pb2+ concentration on Pb2+ accumulation by Saccharomyces cerevisiae and Aureobasidium pullulans.

Pb2+ accumulation by Saccharomyces cerevisiae and Aureobasidium pullulans was inhibited by the initial Pb2+ concentration. In the case of S. cerevisiae, as initial Pb2+ concentrations increased, the accumulated Pb2+ per unit cell dry weight at equilibrium and the time required to reach an equilibrium state increased at low initial Pb2+ concentration. On the contrary, the accumulated Pb2+ decreased at high initial Pb2+ concentration at all pH values. The inhibition effect of initial Pb2+ concentration was delayed by the decrease of pH. However, the maximal Pb2+ accumulation capacity of S. cerevisiae was almost constant regardless of pH values. In the case of A. pullulans, the time required to reach an equilibrium state was independent of the initial Pb2+ concentration. The maximal Pb2+ accumulation capacity of A. pullulans decreased according to the decrease of pH values. However, the initial Pb2+ concentration needed to reach maximal Pb2+ accumulation amount was almost constant.

A study on the sensing characteristics of VOCs for the development of VOCs detector

Volatile organic compounds (VOCs) are one of the popular issues of air pollution in Korea, especially in Ulsan city, where much chemical plants are located. It is necessary to detect the VOCs precisely in order to control the air pollution during the plant operation. In general, to examine the concentration of VOCs, gas chromatography (GC) is used. However, most plant operators are using the easy operating handy VOCs detector, which is imported, because GC is difficult to treat and the installation price is high although it is very useful equipment. Therefore, the development of the VOCs detector becomes one of the urgent issues. In this study, sensing characteristics of selected VOCs for the development of VOCs detector was investigated. Semiconductor sensor and several VOCs such as aliphatic, aromatic, and nonhomogeneous hydrocarbons were used for the experiment. Through the various experiments, sensor used in the experiment has shown high linearity and sensitivity for most VOCs in the range of 1-500 ppm concentration. And correction factors for each VOCs were estimated, which is necessary for the treatment of detector.

Comparison of PB2+ Removal Characteristics Between Biomaterials and Non-biomaterials

The order of Pb2+ removal capacities in chemical adsorbents were found as ion exchange resin > zeolite > granular activated carbon (GAC) > powdered activated carbon (PAC), while in biomass was Aureobasidium pullulans > Saccharomyces cerevisiae > activated sludge. Although Pb2+ removal capacity (mg Pb2+/g) of the activated sludge (30.9) was lower than those of ion exchange resin (167.7) and other pure cultures of A. pullulans (170.4) and S. cerevisiae (95.3), it was higher than those of other chemical adsorbents such as GAC (26.9), PAC (2.1), and zeolite (30.2). The initial Pb2+ removal rates in chemical adsorbents were in the order of PAC > GAC > zeolite > ion exchange resin, while in biomass was A. pullulans > activated sludge > S. cerevisiae. The initial Pb2+ removal rate of activated sludge was higher than those of GAC, zeolite, ion exchange resin and S. cerevisiae cells.