Jin-Soo Chang

Effects of pH and dissolved oxygen on Cr(VI) removal in Fe(0)/H2O systems.

The effects of pH and dissolved oxygen (DO) on aqueous Cr(VI) removal by micro-scale zero-valent iron (Fe(0)/H(2)O system) were investigated. Batch experiments were conducted at pH 4.0, 5.0 and 6.0 under oxic and anoxic conditions. Column experiments were performed at pH 5.0 and 7.5 under oxic condition. Spectroscopic analyses were applied to explain the mechanism of Cr(VI) removal using X-ray absorption near-edge structure (XANES), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Results showed that the kinetics of Cr(VI) removal were fastest at pH 5 under both oxic and anoxic conditions. As a rule, Cr(VI) removal were faster under oxic conditions than under anoxic conditions. Column experiments showed that Cr(VI) removal was about 1.7-fold higher at pH 5 than at pH 7.5. XANES (X-ray absorption near edge structures) results showed that Fe(0) reduced Cr(VI) to Cr(III) under both oxic and anoxic conditions. X-ray diffraction patterns of the Cr(VI)-Fe(0) reaction products suggested partial formation of chromite (FeCr(2)O(4)) at pH 5 and 6 under oxic conditions. However, nano-sized clusters of Cr(III)/Fe(III) hydroxide/oxyhydroxide were formed on the surface of Fe(0) under anoxic conditions. These results indicate that the presence of oxygen in solution plays an important role in control of the kinetic of Cr(VI) removal and in development of various Cr(VI) reduction products.

Immunogenicity of synthetic HIV-1 V3 loop peptides by MPL adjuvanted pH-sensitive liposomes.

A successful HIV-1 vaccine should be capable of generating humoral and cellular immune responses at the same time. The only response shown to be effective in this regard is virus-neutralization antibodies and virus-specific cytotoxic T-lymphocytes (CTL) directed against the viral antigens. In the present study, it is shown that V3 peptides encapsulated pH-sensitive liposomes elicit the virus neutralization antibodies and virus specific CTL response at the same time in Balb/c mice. None of the immunization protocols elicited an antibody response and CTL response when R15K and T26K was used as immunogen without liposomes. In contrast, antibodies and CTL response were detectable in the mice which were immunized with peptide encapsulated pH-sensitive liposomes. Antibody production was confirmed by virus neutralizing assay. CD4+ T-cells are involved in target cell lysis to some degree but CTL activity is mainly due to the CD8 + T-cells. The consistency of the antibody and CTL response was related to the V3 loop peptides size. The T26K (26mer) peptide induced a stronger antibody and CTL response than R15K (15mer) in vivo. Based on the results of this study, T26K was used as a potentially effective HIV-1 vaccine component and T26K encapsulated pH-sensitive liposomes composed of phosphatidylethanolamine-beta-oleoyl-gamma-palmitoyl (POPE)/cholesterol hemisuccinate (CHOH)/monophosphoryl lipid A (MPL) (7:3:0.1, mole ratio) may be used as a potentially immunomodulating adjuvant system for the development of HIV and other viral vaccines.

Bacterial aox genotype from arsenic contaminated mine to adjacent coastal sediment: evidences for potential biogeochemical arsenic oxidation.

The potential biogeochemical redox activity of arsenic was investigated by examining bacterial arsenic (As) redox genes such as aox, ars, and arr in arsenic-contaminated abandoned mine area and adjacent coastal sediments. Consistent with aerobic sediment and water samples from the mine through coastal areas, bacterial genes involing arsenic(V) (arsenate, AsO(4)(3-)) reduction such as arsC and arrA were identified only in a few samples, wheres bacterial aoxB gene encoding arsenite oxidase which is a central role in arsenic(III) (AsO(2)(-)) oxidation of aox operon. This study suggests that evaluation of arsenite-oxidizing bacteria including aox genotype may lead to a better understanding of molecular geomicrobiology in arsenic biogeochemistry, which can be applied to the bioremediation of arsenic contaminated mines along the coast of Gwangyang Bay. In this study, high concentrations of arsenic were observed in the mines and Gwangyang Bay and it was speculated that As(III)-oxidizing bacteria isolated from those highly arsenic-contaminated areas contributed the biogeochemical cycling of arsenic by transforming arsenic species and resulting in change of mobility, though further in situ biogeochemical and/or microbial ecological investigations are needed for confirming the phenomena in natural environment. Acinetobacter junni and Marinobacter sp. which were isolated in the contaminated area contained the aox genes and were able to oxidize As(III) to As(V), which is a more soluble form in oxic aqueous environments and apt to migrate from the mine to the coast. This might suggest a potential of a significant redox role of aox genes of arsenic-oxidizing bacteria in biogeochemical cycle of arsenic.

Biogeochemical cyclic activity of bacterial arsB in arsenic-contaminated mines

Biogeochemical cyclic activity of the ars (arsenic resistance system) operon is arsB influx/efflux encoded by the ecological of Pseudomonas putida. This suggests that studying arsenite-oxidizing bacteria may lead to a better understanding of molecular geomicrobiology, which can be applied to the bioremediation of arsenic-contaminated mines. This is the first report in which multiple arsB-binding mechanisms have been used on indigenous bacteria. In ArsB (strains OS-5; ABB83931; OS-19; ABB04282 and RW-28; ABB88574), there are ten putative enzyme, Histidine (His) 131, His 133, His 137, Arginine (Arg) 135, Arg 137, Arg 161, Trptohan (Trp) 142, Trp 164, Trp 166, and Trp 171, which are each located in different regions of the partial sequence. The adenosine triphosphate (ATP)-binding cassette transports, binding affinities and associating ratable constants show that As-binding is comparatively insensitive to the location of the residues within the moderately stable alpha-helical structure. The alpha-helical structures in ArsB-permease and anion permease arsB have been shown to import/export arsenic in P. putida. We proposed that arsB residues, His 131, His 133, His 137, Arg 135, Arg 137, Arg 161, Trp 142, Trp 164, Trp 166, and Trp 171 are required for arsenic binding and activation of arsA/arsB or arsAB. This arsB influx/efflux pum-ping is important, and the effect in arsenic species change and mobility in mine soil has got a significantly ecological role because it allows arsenic oxidizing/reducing bacteria to control biogeochemical cycle of abandoned mines.

pH-sensitive liposomes as adjuvants for peptide antigens.

Publisher Summary This chapter deals with pH-sensitive liposomes, which are one of the most readily available adjuvants for peptide antigen. Because of low immunogenicity with peptide, a high dose of peptides is required for immunization. As the pH-sensitive liposomes can deliver the encapsulated antigen into the cytosol, the antigen can be processed and presented in the same manner as endogenous antigens and can induce cytotoxic T lymphocyte (CTL) responses more effectively than other adjuvants. Because of the easy preparation process, a minimal difference in adjuvanticity among the preparation methods, and the small amount of peptide antigen necessary to induce CTL response, pH-sensitive liposomes seem to be a good candidate adjuvant for peptide-based CTL vaccines to be used against, for example, hepatitis B and papillomavirus.

DNA sequence homology analysis ofars genes in arsenic-resistant bacteria

Homology ofars (arsenic-resistance system) genes was examined among the indigenous bacteria isolated from the soils and sediments of two abandened Au mines, which are highly contaminated with arsenic. The DNA and amino acid sequence homology of thears determinants were investigated using anars genotype. The isolated showed As(III)-oxidation ability containedarsAB genes encoding the efflux pump as well asarsR andarsD regulator genes. ThearsR andarsD leader gene are required for an arsenic resistance system when the high-homology genes (arsR; pl258 52.09% andarsD;Shewanell sp. 42.33%) are controlled by thears inducer-independent regulatory amino acid sequence. These leader gene were observed under weak acidic conditions in the Myoung-bong (pH; 5.0 to 6.0) and Duck-um (pH; 4.0 to 7.0) mines In addition, the strains with the ability of As (V)-reduction involved thearsC gene homologues, as in the strain CW-16 (Pseudomonas putida). The arsenic-resistance genes in the isolated indigenous bacteria showed varying degrees of amino acid similarity to the homologous genes found in the database (GenBank) such asP. putida KT2440: 39–53% forarsR, 22–42% forarsD, 16–84% forarsA, 26–45% forarsB, 17–44% forarsAB, 37–41% forarsC, and 14–47% forarsH. These findings suggested that the function of the variousars gene in indigenous bacteria existing in weakly oxidative conditions may be the key factor for redox mechanisms and biogeochemical systems in arsenic contaminated soils.

Effect of Dehydration and Rehydration of the pH-Sensitive Liposomes Containing Chimeric gag-V3 Virus Like Particle on Their Long-term Stability

One of the practical limitations with the use of liposomes for delivery of the pharmaceutical substances such as antigens is that liposomes are relatively unstable in storage. In order to extend the stability of liposome in storage without affecting their functional activity, solution-type liposomes were dehydrated to form a structurally intact dry liposomes. Comparative immunological evaluation was carried out for both dry and solution-type liposomes containing gag-V3 chimera, consequently it was found that dry liposomes elicited both humoral and cellular response as efficiently as solution-type liposomes did against the same gag-V3 antigen. Especially, long-term stability of the liposomes was remarkably enhanced by the dehydration made to liposomes without a significant change in its ability to elicit immune responsein vivo. These results indicate that dry pH-sensitive liposome may become an effective delivery and adjuvant system for general vaccine development.