• Journal of Life Science
• /
• v.25 no.11
• /
• pp.1290-1297
• /
• 2015

Studies of the inactivation of a gene encoding pyruvate decarboxylase, pdc, in an ethanol-producing bacterium, Zymomonas mobilis, identified a mutant strain with 50% reduced PDC activity. To evaluate the possibility of a carbon-flux shift from an ethanol pathway toward higher value fermentation products, including pyruvate, succinate, and lactate, fermentation studies were carried out. Despite attempts to silence pdc expression in the wild-type strain ZM4 using cat-inserted pdc and pdc-deleted homologs by electroporation, the strain isolated showed partial gene activation. Fermentation experiments with the PDC mutant strain showed that the reduced expression level of PDC activity resulted in decreased rates of substrate uptake and ethanol production, together with increased pyruvate accumulation of 2.5 g l^-1 , although lactate and succinate concentrations were not significantly enhanced in these modified strains. Despite numerous attempts, no strains were isolated in which complete pdc inactivation occurred. This result indicates that the ethanol fermentation pathway of this bacterium is totally dependent on the activity of the PDC enzyme. To ensure a redox balance of intracellular NAD and NADH levels, other enzymes, such as lactate dehydrogenase for lactate, and enzymes involved in the production of succinic acid, such as pyruvate dehydrogenase (PDH) and malic enzymes, may be needed for their increased end-product production.

• Korean Journal of Microbiology
• /
• v.26 no.3
• /
• pp.215-222
• /
• 1988

The effect of ammonia and glutamine on nitrogenase activity of Rhodopseudomonas sphaeroides was examined. The nitrogenase activity of this strain was inhibited by ammonia and glutamine. When ammonia and glutamine were exhausted, nitrogenase activity promptly resumed at its original rate. Methionine sulfoximine (MSX), irreversible glutamine synthetase (GS) inhibitor, is a structural analogue of glutamate. MSX was used in order to know whether the nitrogenase activity was inhibited by ammonia and glutamine directly or not. The ability of MSX to prevent nitrogenase switch-off by ammonia was found to be dependent upon the phase of culture. When the cells were sampled after 12 hour culture, $500{\mu}M$ MSX would not prevent the nitrogenase switch-off by ammonia. Twenty one percents of GS actibity was inhibited by $500{\mu}M$ of MSX and concentration of released ammonia decreased. But nitrogenase activiy was still inhibited by ammonia. However, nitrogenase switch-off after 20 hours would be prevented by $100{\mu}M$ of MSX. On the other hand, GS activity was ingibited completely by $100{\mu}M$ MSX and concentration of released ammonia somewhat increased. But nitrogenase activity was not inhibited. The data indicated that the inhibition of in vivo nitrogenase actibity of Rp. sphaeroides by ammonia seemed to be mediated by products of ammonia assimilation rather than by ammonia itself.

• Korean journal of food and cookery science
• /
• v.17 no.6
• /
• pp.617-624
• /
• 2001

Gamma irradiation (1-10 kGy) was applied to chicken for the evaluation of their microbiological safety and possible genotoxicity. In 3 kGy-irradiated sample, the growth of psychrophile was inhibited about 1.5 log cycles and no cells were recovered in total microbial counts. All kinds of contaminated microorganism were sterilized by 7 kGy-irradiation. Also, irradiation followed by freeze-storage at the same time was very effective in inhibiting bacterial growth. The genotoxicity of 10 kGy-irradiated chicken was evaluated by Salmonella Typhimurium reversion assay and in vivo micronucleus assay using mouse bone marrow cells. The results were negative in the bacterial reversion assay with S. Typhimurium TA98, TA100, TA1535, and TA1539. Clastogenic effects were not shown in vivo mouse micronucleus assay at 10 kGy-dose tested.

• Food Science and Preservation
• /
• v.22 no.2
• /
• pp.261-266
• /
• 2015

In this study, we investigated the applicability of functional materials by examining various physiological activities with an extract from the Agrimonia pilosa root. The A. pilosa extract showed low cytotoxicity against murine melanoma B16F10 cells. With little or no cytotoxicity at various concentrations, the A. pilosa extract showed high levels of DPPH radical scavenging activity ($ID_{50}$, 20.70 mg/L) and anti-microbial activity against Bacillus subtilis, Escherichia coli, and Candida albicans. In particular, it had a high level of anti-microbial activities against Gram-positive bacteria. These results suggest that the A. pilosa extract can be used as a natural preservative. It also showed inhibition of tyrosinase activity ($ID_{50}$, 90.18 mg/L), as does kojic acid ($ID_{50}$, 89.13 mg/L), and especially, a higher decrease in melanin content ($ID_{50}$, 62.5 mg/L) than the arbutin level ($ID_{50}$, 100.7 mg/L) as a positive control. These findings suggest that the A. pilosa extract inhibits melanin synthesis by suppressing the intracellular tyrosinase expression. These results indicate that the A. pilosa extract may be an effective material for functional cosmetics, such as skin whitening materials.

• Applied Biological Chemistry
• /
• v.50 no.4
• /
• pp.257-261
• /
• 2007

Tolaasin, a peptide toxin produced by Pseudomonas tolaasii, causes a serious disease on the cultivated mushrooms, known as brown blotch disease. Hemolysis using red blood cells was designed to measure the cytotoxicity of tolaasin molecules. Since tolaasin has two amine groups near the C-terminus, its membrane binding will be dependent on the ionic states of the amine groups. When the tolaasin peptide was titrated, its titration curve indicated the presence of titratable amine(s) at pH ranges from 7.0 to 9.6. When the pH-dependence of tolaasin-induced hemolysis was measured at various pHs, hemolysis was more efficient at alkaline pHs. In order to measure the membrane binding activity of tolaasin at different pHs, RBCs were incubated with tolaasin molecules for short time periods and washed out with fresh buffer. Because of the tolaasin binding during the preincubation period, fast hemolyses were observed at pH 8 or higher. These results imply that non-charged or less positively charged states of tolaasin molecules easily bind to membrane and show high hemolytic activity.

• Korean Journal of Microbiology
• /
• v.24 no.2
• /
• pp.133-140
• /
• 1986

Extracts of CO-autotrophically grown cells of Acinetobacter sp. 1 were shown to use thionin, methylene blue, or 2,6-dichlorophenol-indophenol, but not NAD, NADP, FAD, or FMN, as electron acceptors for the oxidation of CO under strictly anaerobic conditions. The CO dehydrogenase (CO-DH) in the thes bacterium was found to be an inducible enzyme. The enzyme activity was determined by an assay based on the CO-dependent reduction of thionin. Maximal reaction rates were found at pH 7.5 and $60^{\circ}C$, and the Arrhenius plot revealed an activation energy of 6.1 kcal/mol(25.5kJ/mol). THe $K_m$ m/ for CO was $154{\mu}M$. Known metalchelating agents tested had no effects on the CO-DH activity. No divalent cations tested affect the enzyme activity significantly escept $Cu^{2+}$ which suppressed the activity completely. The enzyme was inhibited by glucose and succinate. The same extracts catalyzed oxidation of hydrogen gas and formate with thionin as electron acceptor. The CO-DH of Acinetobacter sp. 1 was to have no immunological relationship with that of Pseudomonas carboxydohydrogena.

• Microbiology and Biotechnology Letters
• /
• v.36 no.1
• /
• pp.82-85
• /
• 2008

Hyungbangjihwang-Tang (HT), an Oriental herbal formula, has been known to play a role which helps to recover vigor of human in the Orient. In this study, antibacterial substance (HTI) was purified from the ethyl-acetate extracts of HT by using $SiO_2$ column chromatography and HPLC, and the antibacterial effects of HTI were investigated. By using the CLSI broth micro-dilution assay, the activity of HTI was evaluated against human pathogenic Gram-positive and Gram-negative bacterial strains including the clinical isolates of methicillin-resistant Staphylococcus aureus. The results demonstrated that HTI showed broad spectrum antibacterial activities against all bacterial strains tested. In conclusion, HTI is an interesting new molecule for its potential in anti-infective drug discovery and for future studies on activity-structure relationship through analysis of its chemical structure.

• Korean Journal of Plant Resources
• /
• v.28 no.2
• /
• pp.153-157
• /
• 2015

In this study, we investigated the applicability of functional materials by examining a variety of physiological activities with the extract of Cleyera japonica leaf. Cleyera japonica extract showed a low cytotoxicity against murine melanoma B16F10 cells. In little or no cytotoxicity at concentrations, we showed that the treatment with Cleyera japonica extract resulted in a significant increase in the DPPH radical scavenging activity (IC₅₀, 22.90 ㎎/L), similar to ascorbic acid (IC₅₀, 18.65 ㎎/L) and anti-microbial activities against Bacillus subtilis, Escherichia coli, and Candida albicans. In particular, anti-microbial activities against Gram-positive bacteria was high. These results suggest that Cleyera japonica extract could be used as a natural preservative. Additionally, Cleyera japonica extract showed the inhibition of tyrosinase activity (IC₅₀, 178.90 ㎎/L), similar to kojic acid (IC₅₀, 89.13 ㎎/L) and decreased melanin content (IC₅₀, 101.90 ㎎/L) higher than the control arbutin level (IC₅₀, 100.65 ㎎/L), especially. Therefore, these results indicate that Cleyera japonica extract may be an effective material for functional cosmetics such as skin whitening materials.

• Korean Journal of Food Science and Technology
• /
• v.22 no.4
• /
• pp.492-495
• /
• 1990

In succession to the previous paper(Korean J. Food Sci. and Techn., 21(2), 300, 1989), to investigate effect of salting process on physico-chemical properties of Korean radish cubes processed for kakdugi Ascorbic acid content, ${\alpha}-amylase$ activity, the penetration rate of glucose and red-pepper juice into the radish cubes, and aerobic microbial counts (bacteria, yeast and mold) were investigated during salting (packout ratio : 1:1g/ml) of radish-cube$(2{\times}2{\times}2cm)$ for kakdugi in the 15%(w/v) sodium chloride solution. For 6hr salting, ascorbic acid was reduced from 38.5mg% to 15.7 mg%, ${\alpha}-amylase$ activity was gradually increased until 5hr salting, and then deceased, Amount and rate of penetration of glucose and red-pepper juice(on base of redness) into the salted radish cube were both higher than raw cubes, and microbial counts were decreased, and mostly within one hour of salting.

• Food Science and Preservation
• /
• v.5 no.4
• /
• pp.380-385
• /
• 1998

The sensitivity of various pathogenic bacteria(Aeromonas hydrophila, Escherichia coli O157:H7, Listeria monocytogenes, Staphylococcus aureus 196E, Salmonella typhimurium) to the ethanol extract of pine needle was tested. Tryptic soy broth containing 0-2%(w/v) of the ethanol extract of pine needle was inoculated with 10$^4$-10$\^$6/ CFU/ml of pathogenic bacteria and incubated at 35$^{\circ}C$ for 48 hours. Gram positive bacteria(L. monocytogenes and S. aureus 196E) and 1 Gram negative bacteria(A. hydrophila) were more sensitive than E. coli O157:H7 and S. typhimurium in the ethanol extract of Pine needle. Gram negative bacteria(E. coli O157:H7 and S. typhimurium) were not inhibited at 1% and they were slightly inhibited at 2% ethanol extract of pine needle. S. aureus was the highest sensitivity, followed by A. hydrophila, L. monocytogenes E. coli O157:H7 in that order. S. typhimurium was the most resistant to the ethanol extract of pine needle.