Self-cloning of the Catalase Gene in Environmental Isolates Improves Their Colony-forming Abilities on Agar Media

Hydrogen peroxide (H₂O₂) inhibits microbial growth at a specific concentration. However, we previously isolated two environmental bacterial strains that exhibited sensitivity to a lower H₂O₂ concentration in agar plates. Putative catalase genes, which degrade H₂O₂, were detected in their genomes. We herein elucidated the characteristics of these putative genes and their products using a self-cloning technique. The products of the cloned genes were identified as functional catalases. The up-regulation of their expression increased the colony-forming ability of host cells under H₂O₂ pressure. The present results demonstrated high sensitivity to H₂O₂ even in microbes possessing functional catalase genes.

Primary Ammonium Terephthalate Salts with High Moisture Resistance and Their Use in the Detection of OH Radicals

A novel and practical method is proposed for the detection of gaseous OH radicals using a moisture-resistant organic salt composed of terephthalic acid (TPA) and n-alkylamine. When the alkyl chain length was greater than 8, the organic salt had a crystal structure in which the alkyl chains were arranged parallel to each other and zero-dimensional voids were adjacent to terephthalate (TA). Since the parallelly arranged alkyl chains acted as a hydrophobic block, the organic salts had excellent humidity durability. The highly hydrophobic bis(n-octylammonium) terephthalate (nOA-TA) powder was exposed to gaseous OH radicals generated by a low-pressure mercury lamp and a fluorescence response suggesting the formation of bis(n-octylammonium) hydroxyterephthalate (nOA-HTA) was observed. The presence of the zero-dimensional voids in the nOA-TA crystal caused the formation of nOA-HTA. In addition, a sheet was prepared in which nOA-TA crystals were uniformly immobilized in the pores of a membrane filter, and the spatial distribution of OH radicals was evaluated.

On-line Measurement of Sub-ppb Level Hydrogen Peroxide in Ultrapure Water Production Process

An on-line H2O2 analyzer was developed for application to the ultrapure water production process, using a gasometric method. The analyzer consists of a dissolved oxygen (DO) sensor and analyzer, a catalyst that converts H2O2 to O2, and a computer that stores the DO data. H2O2 concentrations were calculated by measuring the change in DO concentration before and after the catalyst and using the calculation formula presented in this study. In order to accurately analyze a sub-ppb level of H2O2, a DO meter which can correctly measure the DO concentration at the ppb level was applied. An ion exchange resin with Pd, was selected as an appropriate catalyst since it could decompose 99% of H2O2 to O2 at a space velocity of 120/h. The minimum analysis time was 20 min, and the detection limit was observed to be 0.27 ppb. When the DO concentration of the sample was 1.5 ppb or lower, an H2O2 concentration of 1 ppb or lower was successfully measured. Good correlation, with an R2 value of 0.99, was observed between the measured and calculated H2O2 concentrations.

Enzyme-less amperometric sensor manufactured using a Nafion-LaNiO3 nanocomposite for hydrogen peroxide

In the present study, an enzyme-less amperometric sensor based on Nafion (NF) and a LaNiO3 (LNO) nanocomposite was constructed for H2O2 detection. LNO from the perovskite group was mixed with NF as an effective solubilizing and stabilizing agent that was used as a novel modifier for modification of the glassy carbon electrode (GCE). The designed sensor showed a desirable electrocatalytic response toward H2O2 reduction. The calibration curve revealed two linear portions in the concentration ranges of 0.2-50 μM and 50-3240 μM, and the detection limit was 0.035 μM. The accuracy of the interference-free sensor was checked by recovery analysis in serum samples.

Factors controlling the degradation of hydrogen peroxide in river water, and the role of riverbed sand

Diurnal changes of H₂O₂ in river water during mid-summer were investigated. H₂O₂ in river water increased with the increase in intensity of solar radiation in the morning, and reached a maximum at 14:00, although solar radiation reached a maximum around 12:00. In the afternoon, a gradual decrease in H₂O₂ was observed, and H₂O₂ reached a minimum just before sunrise. Degradation rate constants determined using unfiltered river water samples were 0.081-0.161 h^-1, corresponding to a half-life of 4.3-8.5 h. We simulated diurnal changes in H₂O₂ using a simple formation, accumulation, and degradation model for static water using formation and degradation rate constants. The results of the modeling suggested that in situ degradation rate constants in rivers could be faster than those determined for unfiltered river water samples. Experiments using river sand indicated that riverbed sand could play an important role in H₂O₂ decay in rivers. We discussed the decomposition process of H₂O₂ in rivers.

Photoformation of reactive oxygen species and their potential to degrade highly toxic carbaryl and methomyl in river water

Reactive oxygen species (ROS) including singlet oxygen (¹O₂) and hydroxylradicals (OH) photogenerated in natural waters play important roles in indirect photolysis of man-made pollutants. This study was conducted to investigate how the generation of these two ROS influences the degradation of two highly toxic insecticides (methomyl and carbaryl) in river water. To accomplish this, the reaction rate constants of ¹O₂ and OH with carbaryl and methomyl were determined; the degradation rate constants of the tested insecticides in ultrapure water (direct photolysis) and in river water in the presence and absence of ¹O₂ and OH scavengers were also measured. The rate constants for the reaction of OH with carbaryl and methomyl were found to be (14.8 ± 0.64) × 10⁹ and (4.68 ± 0.52) × 10⁹ M^-1 s^-1, respectively. The reaction rate constant of ¹O₂ with carbaryl (2.98 ± 0.10) × 10⁵ M^-1 s^-1, was much higher than that of methomyl (<10⁴ M^-1 s^-1). Indirect photolysis by OH accounted for 63% and 62%, while ¹O₂ accounted for 26% and 30% and direct photolysis accounted for 1.4% and 7% of methomyl and carbaryl degradation, respectively. The high degradation rate in river water demonstrated by both insecticides suggests that indirect photolysis mediated by OH is an important means of their degradation in river water. In addition, kinetic calculations of OH-mediated degradation rate constants of the compounds agrees with their experimentally-determined values thereby confirming the importance of OH towards their degradation.