Dong Seog Kim

Process of Pb2+ accumulation in Saccharomyces cerevisiae

Most of the Pb2+ taken up by Saccharomyces cerevisae was deposited in the inner part of the cells after 2 h. In the Pb2 accumulation experiments, the time to reach an equilibrium state was significantly shortened from 96 h to 24 h as the cell dry weight increased from 0.56 g/l to 5.18 g/l. The penetration time of Pb2+ to reach on the interacellular region (2 h) was quite different from that on the extracellular region (3 min). In the case of S. cerevisiae, the first step which a Pb2+ binds to cell wall within 3[f]5 min is metabolism-independent and the second step within 24 h is metabolism-dependent followed by the third step which is metabolism-dependent or -independent after 24 h.

Comparison of different sorbents (inorganic and biological) for the removal of Pb2+ from aqueous solutions

In an attempt to evaluate the suitability of activated sludge for Pb 2+ removal, a comparative study was carried out using several chemical adsorbents and three types of biomass. The order of Pb 2 removal capacities for chemical adsorbents was found to be: ion exchange resin > zeolite > granular activated carbon (GAC) > powdered activated carbon (PAC), while for biomass the order was Aureobasidium pullulans > Saccharomyces cerevisiae > activated sludge. Although Pb 2+ removal capacity (mg Pb 2+ g -1 ) of the activated sludge (30.9) was lower than those of the 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 (26.0), PAC (2.1), and zeolite (30.2). The initial Pb 2 removal rates for the chemical adsorbents were in the order of PAC > GAC > zeolite > ion exchange resin, while for the biomass samples it was A.pullulans > activated sludge > S.cerevisiae. The initial Pb 2+ removal rate of activated sludge was higher than those of GAC, zeolite, ion exchange resin and S.cerevisiae cells. Therefore, it was concluded that activated sludge that has been used in a municipal wastewater facility can be effectively used in heavy metal removal processes, in situ.

Comparison of Pb2 accumulation characteristics between live and dead cells of Saccharomyces cerevisiae and Aureobasidium pullulans

Pb2+ accumulation processes between live and dead cells of Saccharomyces cerevisiae and Aureobasidium pullulans are different. In the case of S. cerevisiae, the Pb2+ accumulation capacity of the live cells was higher than that of the dead cells but they showed reversed initial Pb2+ accumulation rates. On the contrary, A. pullulans used a different process due to the existence of extracellular polymeric substances, which allowed both the capacity and the initial rate of Pb2+ accumulation in the live cells to be higher than those in the dead cells.

Effect of extracellular polymeric substances (EPS) on Pb2+ accumulation by Aureobasidium pullulans

Abstract In Pb2+ accumulation by Aureobasidium pullulans, the time to reach an equilibrium state was not dependent on the initial cell dry weight. The Pb2+ accumulation capacity was increased from 56.9 to 215.6u2009mg Pb2+/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 Pb2+ accumulated only on the surface of the intact cells of A. pullulans due to the existence of EPS, whereas Pb2+ penetrated into the inner cellular parts of the EPS-extracted cells.

Enzymatic production of inulo-oligosaccharides from chicory juice

Batchwise production of inulo-oligosaccharide from chicory juice was carried out by an endoinulinase from Pseudo-monas sp. The maximum yield of oligosaccharides (OS) was about 80% in total sugar basis with substrate at 30–100 g/l. Compared with pure inulin of the same origin as a substrate, the same OS yield was obtained but it showed quite a different product distribution in degree of polymerization (DP) and sugar composition, where DP2, DP3 and DP4 were major components.

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.

Effect of pH on Pb2+ accumulation in Saccharomyces cerevisiae and Aureobasidium pullulans

Abstract The optimum pH conditions of Pb2+ accumulation in Saccharomyces cerevisiae and Aureobasidium pullulans were 4∼5 and 6∼7, respectively. The initial Pb2+ accumulation rates according to the increase of initial Pb2+ concentration and pH were increased both in S. cerevisie and A. pullulans. And the initial Pb2+ accumulation rate of A. pullulans was much higher than that of S. cerevisiae because of the difference of Pb2+ accumulation mechanism. The Pb2+ accumulation isotherm of S. cerevisae obeyed a fully competitive inhibition, whereas that of A. pullulans showed a mixed inhibition of competition and non-competition associated with the proton (H+) as an accumulation inhibitor.

Wastewater Treatment in a Packed-Bed Reactor with Immobilized Cells onto a New Ceramic Carrier

A new porous ceramic carrier based on casting sand, sawdust and zeolite was used to immobilize microorganisms for continuous wastewater treatment in a packed-bed bioreactor. Scanning electron microscopy showed that the ceramic carrier has a high porosity with diameters of around 5~300µm. Immobilization capacity of the carrier was 62 mg/ g dry carrier, in terms of mixed liquor volatile suspended solids. When synthetic wastewater (chemical oxygen demand 250 mg/l) as a model feed solution and 30 mg kaolin/l as a suspended solid (SS) were used, the removal efficiency as measured by the total organic carbon and SS were 91% and 71%, respectively, at a hydraulic retention time of 3 h.

Effect of extracellular polymeric substances (EPS) on the attachment of activated sludge

Abstract Extracellular polymeric substances (EPS) were removed by mechanical (high-speed centrifugation) and chemical (EDTA treatment) methods. The number of attached microorganisms decreased from 33.0u2009×u2009107 CFU/cm2 to 17.5u2009×u2009107 CFU/cm2 and 12.5u2009×u2009107 CFU/cm2, respectively. When the activated sludge was treated with polysaccharide-oxidizing agent (sodium meta periodate) and protease (pronase E), the number of attached microorganisms decreased to 41% and 43.5%, respectively. Transmission electron microphotographs showed that polysaccharide-oxidizing agent and protease treatment caused the removal of filamentous extracellular structures.