Salt Stress Tolerance of Methylotrophic Bacteria Methylophilus sp. and Methylobacterium sp. Isolated from Coal Mine Spoils

Two methylotrophic strains of Bina coalmine spoil BNV7b and BRV25 were identified based on physiological traits and 16S rDNA sequence as Methylophilus and Methylobacterium species.' The strains exhibited similar carbon utilization but differed in N utilization and their response to the metabolic inhibitors. Methylophilus sp. was less tolerant to salt stress and it viability declined to one tenth within 4 h of incubation in 2M NaCI due to membrane damage and leakage of the intracellular electrolytes as evident from malondiaaldehyde (MDA) assay. In 200 mM NaCI, they exhibited increased superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) activity while in 500 mM NaCI, enzyme activities declined in Methylophilus sp. and increased in Methylobacterium sp. Among exogenously applied osmoprotectants proline was most efficient; however, polyols (mannitol, sorbitol and glycerol) also supported growth under lethal NaCI concentration.

Isolation and Characterization of Halotolerant Aerobic Bacteria From Oil Reservoir

Beberapa bakteria halotoleran telah berjaya dipencilkan daripada sampel air masin telaga minyak Semangkok di mana ujian biokimia dan morfologi telah dijalankan bagi bakteria ini. Hampir semua bakteria yang dipencilkan tergolong di dalam genus Bacillus. Sebahagian besar daripada pencilan berkeupayaan untuk hidup di dalam medium pertumbuhan yang mengandungi kerosen sebagai sumber karbon utama dan tenaga dan berkeupayaan untuk hidup di dalam medium dengan kepekatan NaCI diantara 10–15%. Ujian ketegangan antara permukaan (IFT) menunjukkan pencilan menghasilkan biosurfaktan. Enam daripada sembilan pencilan menghasilkan eksopolisakarida di dalam medium pertumbuhan yang mungkin penting di dalam MEOR. Kata kunci: Bakteria; pencirian; pengasingan; Surfaktan; Eksopolisakarida Several halotolerant bacteria were isolated from brine samples from Semangkok oil reservoir. Biochemical and morphological characterization of the bacteria were carried out. These bacteria are gram positive spore formers and have been identified as belonging to the genus Bacillus. Most of the isolates could grow in medium containing kerosene as sole carbon source and energy and tolerate NaCI concentration up to 15%. Interfacial tension and surface tension tests showed that the bacteria were capable of producing biosurfactant. Six out of nine were able to produce exopolysaccharide. We believe these isolate could be appointed as future biopolymer producer especially for microbial enhanced oil recovery (MEOR). Keywords: Bacteria; Characterization; Isolation; Surfactant; Exopolysaccharides.

Sectrophotometric Investigation of U(VI) Chloride Complexation in the Naci/NaClO4 system

Post closure radioactive release scenarios from geologic salt formation, such as the WIPP (Waste Isolation Pilot Plant) (USA) include hydrologic transport of radionuclides through a chloride saturated aquifer. Consequently, the understanding of actinide solution chemistry in brines is essential for modeling requiring accurate knowledge of the interaction between AnO22+ and chloride ions. Complexation constants of two U(VI) chloride species UO2Cl+ and UO2Cl20 have been intensively studied for about 40 years using different methods. However, large uncertainties reflect the general difficulty in determining accurate stability constants of weak complexes. In order to model the behavior of U(VI) in brines, we studied the formation of its chloride complexes by UV-Vis spectroscopy as a function of the NaCI concentration at 25 °C. The experiments were performed at constant ionic strength by varying the concentration ratio of NaCI and NaClO4. Deconvolution resulted in single component absorption sepectrum for UO2Cl+ and UO2Cl20. The apparent stability constants of UO2Cl+ and UO2Cl20 are determined at different ionic strengths. The experimental data are used to parameterize using the SIT approach.

Sorption of Uranium(6+) and Neptunium(5+) by Surfactant-Modified:Natural Zeolites

Experiments were conducted to determine the ability of surfactant-modification to enhance the ability of natural zeolites to sorb U(6+) and Np(5+). Natural zeolite material, comprised mainly of clinoptilolite and treated with the cationic surfactant exadecyltrimethylammonium-bromi(le (IDTMA), was reacted with U(6+) and Np(5+) solutions open to the atmosphere and having a range of radionuclide concentration, pH, and NaCI concentration. The results indicate surfactantmodification of the zeolite enhances its ability to sorb U(6+), particularly at pHs greater than six where U(6+) sorption on unmodified zeolite is typically low due to formation of anionic U(6+) aqueous carbonate complexes. In contrast, there is little enhancement of Np(5+) sorption onto surfactant-modified zeolite. The presence of chloride anions in solution makes surfactantmodification less effective. The enhanced sorption of U(6+) is interpreted to be due to anion exchange with counterions on the external portion of a surfactant bilayer or admicelles.

Behavior of Listeria spp. in Smoked Fish Products Affected by Liquid Smoke, NaCI Concentration, and Temperature

The growth, survival, and death of Listeria monocytogenes were studied in a synthetic medium as a function of temperature, NaCI content, and amount of liquid smoke, and the findings were validated in smoked fish products. The smoke preservative compound was simulated by adding liquid smoke, and the concentration was expressed as phenol concentration. The growth of L. monocytogenes was limited at a temperature as low as 4°C or at a phenol concentration as high as 20 ppm. The predicted values were obtained using a mathematical model established in liquid medium in a previous study. They accurately fit values observed in L. monocytogenes challenge tests on smoked fish. After 21 days of storage the deviation between the predicted and experimental values was within 0.5 log for 60% of the data. This model may be useful in predicting Listeria contamination in smoked fish. Moreover, this study emphasizes the importance of phenol concentration to control the growth of Listeria spp. in smoked food products.

Crevice Corrosion - NaCI Concentration Map for Grade-2 Titanium at Elevated Temperature

ABSTRACTThe repassivation potential, ER, for metal/metal-crevice of Commercially Pure Titanium, C.P.Ti, was determined in NaC1 solutions at temperatures up to 250C. The ER has its least noble value near 100C and becomes more noble as the temperature increases. As shown in previous research[1], the shrinkage of the repassivation region should continue with increasing temperatures. However, in conducting this same experiment at temperatures higher than 100C, an examination of the NaCI concentration - temperature - crevice corrosion map verifies that the repassivation region began to expand again when the temperature exceeded 140C. This expansion continued as the temperature continued to increase.