scholarly journals Chemical Forms of Selenium in the Metal-Resistant Bacterium Ralstonia metallidurans CH34 Exposed to Selenite and Selenate

2005 ◽  
Vol 71 (5) ◽  
pp. 2331-2337 ◽  
Author(s):  
Géraldine Sarret ◽  
Laure Avoscan ◽  
Marie Carrière ◽  
Richard Collins ◽  
Nicolas Geoffroy ◽  
...  
Keyword(s):  
Transformation Product ◽  
Lag Phase ◽  
Elemental Selenium ◽  
Experimental Conditions ◽  
Phase Duration ◽  
Contact Exposure ◽  
Ralstonia Metallidurans ◽  
A Minor ◽  
X Ray Absorption ◽  
Kinetics Of

ABSTRACT Ralstonia metallidurans CH34, a soil bacterium resistant to a variety of metals, is known to reduce selenite to intracellular granules of elemental selenium (Se0). We have studied the kinetics of selenite (SeIV) and selenate (SeVI) accumulation and used X-ray absorption spectroscopy to identify the accumulated form of selenate, as well as possible chemical intermediates during the transformation of these two oxyanions. When introduced during the lag phase, the presence of selenite increased the duration of this phase, as previously observed. Selenite introduction was followed by a period of slow uptake, during which the bacteria contained Se0 and alkyl selenide in equivalent proportions. This suggests that two reactions with similar kinetics take place: an assimilatory pathway leading to alkyl selenide and a slow detoxification pathway leading to Se0. Subsequently, selenite uptake strongly increased (up to 340 mg Se per g of proteins) and Se0 was the predominant transformation product, suggesting an activation of selenite transport and reduction systems after several hours of contact. Exposure to selenate did not induce an increase in the lag phase duration, and the bacteria accumulated approximately 25-fold less Se than when exposed to selenite. SeIV was detected as a transient species in the first 12 h after selenate introduction, Se0 also occurred as a minor species, and the major accumulated form was alkyl selenide. Thus, in the present experimental conditions, selenate mostly follows an assimilatory pathway and the reduction pathway is not activated upon selenate exposure. These results show that R. metallidurans CH34 may be suitable for the remediation of selenite-, but not selenate-, contaminated environments.

scholarly journals Mobilization of Selenite by Ralstonia metallidurans CH34

2001 ◽  
Vol 67 (2) ◽  
pp. 769-773 ◽  
Author(s):  
Murielle Roux ◽  
Géraldine Sarret ◽  
Isabelle Pignot-Paintrand ◽  
Marc Fontecave ◽  
Jacques Coves
Keyword(s):  
Alcaligenes Eutrophus ◽  
Culture Conditions ◽  
Lag Phase ◽  
Elemental Selenium ◽  
Kinetics Analysis ◽  
X Ray ◽  
Polluted Sites ◽  
Ralstonia Metallidurans ◽  
X Ray Absorption ◽  
Bioremediation Processes

ABSTRACT Ralstonia metallidurans CH34 (formerlyAlcaligenes eutrophus CH34) is a soil bacterium characteristic of metal-contaminated biotopes, as it is able to grow in the presence of a variety of heavy metals. R. metalliduransCH34 is reported now to resist up to 6 mM selenite and to reduce selenite to elemental red selenium as shown by extended X-ray absorption fine-structure analysis. Growth kinetics analysis suggests an adaptation of the cells to the selenite stress during the lag-phase period. Depending on the culture conditions, the medium can be completely depleted of selenite. Selenium accumulates essentially in the cytoplasm as judged from electron microscopy and energy-dispersive X-ray analysis. Elemental selenium, highly insoluble, represents a nontoxic storage form for the bacterium. The ability of R. metallidurans CH34 to reduce large amounts of selenite may be of interest for bioremediation processes targeting selenite-polluted sites.

scholarly journals Substantiation of the sell-by date of food products

2020 ◽  
Vol 52 (1) ◽  
pp. 59-63
Author(s):  
S.M. Kuzminskiy ◽  
T.V. Adamchuk ◽  
О.М. Holinko ◽  
N.P. Levytska
Keyword(s):  
Food Products ◽  
Storage Conditions ◽  
Lag Phase ◽  
Contamination Level ◽  
Second Phase ◽  
Phase Duration ◽  
Normative Documents ◽  
Culture Development ◽  
Storage Distribution ◽  
Kinetics Of

Objective of the Work. The overview of current methodical approaches for experimental substantiation of the sell-by date of food products. Methods and Materials. Data analysis of scientific literature and normative documents on methods of substantiation of the sell-by date of food products. Results and Discussion. Sell-by date is a period since product’s manufacture, during which it maintains its safety and quality (including nutritional value) within reasonably foreseeable conditions of storage, distribution and consumption. In the case of new products (recipes) introduction it is necessary to review the sell-by date, and its extending as the need arises. The main aspects of microbiological substantiation of the sell-by date of food products are considered. The identification of microbial hazard for particular product is the first phase of the work. The second phase of the work is to determine the kinetic parameters of precise microorganism’s accumulation to maximum permitted level within regulated and aggravated conditions of product’s storage. Conclusions. In the process of microbiological substantiation of the sell-by date of food products it should be taken into consideration the presence of leading pathogen and causative microorganisms of microbial spoilage, the initial contamination level, the lag phase duration of germ culture development, variations between strains, the kinetics of microorganisms’ accumulation within the product in real and aggravated storage conditions, the indetermination connected with biological nature of microorganisms and their inhomogeneous allocation within the product, the limitation for shortcut research methods (if applicable). The decision rule should be based on the consumer’s risk concept. Key Words: food products, sell-by date, substantiation, microbiological indicators.

Photochemie von Ribonucleinsäuren

1964 ◽  
Vol 19 (9) ◽  
pp. 815-830 ◽  
Author(s):  
Heinz Schuster
Keyword(s):  
Pyrimidine Ring ◽  
Alkaline Treatment ◽  
Neutral Solution ◽  
Experimental Conditions ◽  
Compound A ◽  
Dark Reaction ◽  
Ribose Phosphate ◽  
Minor Part ◽  
A Minor ◽  
Kinetics Of

Irradiation of uridylic acid (Up) in buffer (at 254 mµ or 280 mµ) yields the hydrated molecule (UpH2O), which on subsequent alkaline treatment decomposes to Up (65%) and a new compound A (35%) with the pyrimidine-ring opened. Irradiation in ice (254 mµ) leads to the formation ofthe uridylic acid dimer (Up/Up), which on re-irradiation reverts to Up (230 mµ, in neutral solution) or compound A, via Up and UpH2O) (254 mµ, in alkaline solution).Similarly the hydrated cytidylic acid (CpH2O) is formed by irradiation of cytidylic acid (Cp) in buffer (254 mµ). In a subsequent dark reaction most of the CpH2O-molecules revert to Cp, a minor part being deaminated to UpH2O. Alkaline treatment of an irradiated Cp-solution yields Cp, Up and compound A, the latter two arising by decomposition of UpH2O. Neither Cp nor Up dimers were found after irradiation of Cp in ice (254 mµ).All the photoproducts of Up and Cp, in which the pyrimidine-ring was still preserved, lost 1 - 3% of their phosphoric acid (Pi) under the experimental conditions.The alkaline decomposition of UpH2O is used as a method for the titration of hydrated uracil residues in irradiated ribonucleic acid (RNA). Following irradiation (254 mµ) the RNA is degraded by alkali completely to mononucleotides and three new photoproducts: compound A, ribose phosphate, and another compound B, which behaves like Up dimer. Form the amount of compound A found, the number of hydrated uracils originally formed can be calculated. Furthermore the kinetics of the formation of the photoproducts are studied.The biological implications of these studies are discussed.

scholarly journals Contraction kinetics of intact and skinned frog muscle fibers and degree of activation. Effects of intracellular Ca2+ on unloaded shortening.

1985 ◽  
Vol 86 (4) ◽  
pp. 479-500 ◽  
Author(s):  
J Gulati ◽  
A Babu
Keyword(s):  
Experimental Conditions ◽  
Bathing Medium ◽  
Internal Load ◽  
Skinned Fiber ◽  
Fiber Properties ◽  
Partial Activation ◽  
A Minor ◽  
Kinetics Of ◽  
Speed Of Shortening

This study addresses a long-standing controversy on the effects of the degree of activation on cross-bridge kinetics in vivo, by utilizing isolated intact and skinned fiber preparations. Steady force levels ranging from 0.1 to 0.76 P0 were achieved at 0 degrees C with temperature-step stimulation of intact fibers by varying the amount of caffeine in the bathing medium. The speed of unloaded shortening (by slack test) was found to be practically constant, which suggests that intracellular Ca2+ in the intact preparation has relatively little effect on isotonic shortening. Along with the results on tetanically stimulated fibers (force, P0), we observed a minor but significant trend for the speed to decline with lowered force levels. This trend is explained by the presence of a constant internal load equaling approximately 1% P0. The effect of Ca2+ on the shortening behavior of skinned fibers was examined at 0 and 10 degrees C. At 0 degrees C, there was practically no effect of Ca2+ on the shortening response in slack tests. At 10 degrees C, there was also no Ca2+ effect during the first activation cycle, but in subsequent cycles the speed of shortening was reduced during partial activation, which indicates that there were permanent changes in the fiber properties under these experimental conditions. The latter result could be explained if the internal load had increased to approximately 5% P0 in the modified skinned fiber (compared with 1% P0 in intact fiber). These findings show that isotonic contraction of frog fibers is intrinsically unaffected by the variations in intracellular Ca2+ that modulated the force over a nearly complete range. The results provide support for the idea that Ca2+ influences the force development in vivo by on-off switching mechanisms.

scholarly journals KINETICS OF THROMBIN INACTIVATION AS INFLUENCED BY PHYSICAL CONDITIONS, TRYPSIN, AND SERUM

1940 ◽  
Vol 24 (2) ◽  
pp. 169-188 ◽  
Author(s):  
Anthony J. Glazko ◽  
John H. Ferguson
Keyword(s):  
Major Effect ◽  
Order Reaction ◽  
Minor Effect ◽  
Serum Tryptase ◽  
Experimental Conditions ◽  
First Order ◽  
Physical Conditions ◽  
A New Technique ◽  
A Minor ◽  
Kinetics Of

1. A new technique for studying the progressive inactivation of thrombin is described. 2. Thrombin inactivation follows the kinetics of a first order reaction. 3. The rate constant of the inactivation reaction increases with temperature and pH (5.0 → 10.0), and also with the presence of crystalline trypsin, or serum. The rate varies for different thrombin preparations, even under the same experimental conditions. 4. The temperature characteristics of the reaction indicate that thrombin is associated with protein. 5. Thrombin preparations are most stable at pH 4 to 5, even when trypsin or serum is added. 6. The progressive inactivation is believed to be due to two mechanisms: (1) a major effect, thought to be the action of a "serum-tryptase," which is usually present in the thrombin preparations, and (2) a minor effect, probably attributable to denaturation of thrombin-protein. 7. Sources of the thrombinolytic factor (serum-tryptase) and its implications in the general theory and practical problems of blood coagulation and antithrombic action are briefly discussed.

scholarly journals Inhibitory Effects of Arginine on the Aggregation of Bovine Insulin

2012 ◽  
Vol 2012 ◽  
pp. 1-7 ◽  
Author(s):  
Michael M. Varughese ◽  
Jay Newman
Keyword(s):  
Bovine Insulin ◽  
Insulin Concentration ◽  
Lag Phase ◽  
Aggregation Kinetics ◽  
Initial Growth ◽  
Inhibitory Effects ◽  
Phase Duration ◽  
Quench Temperature ◽  
Increasing Temperature ◽  
Kinetics Of

Static and dynamic light scattering were used to investigate the effects of L-arginine, commonly used to inhibit protein aggregation, on the initial aggregation kinetics of solutions of bovine insulin in 20% acetic acid and 0.1 M NaCl as a model system for amyloidosis. Measurements were made as a function of insulin concentration (0.5–2.0 mM), quench temperature (60–85°C), and arginine concentration (10–500 mM). Aggregation kinetics under all conditions had a lag phase, whose duration decreased with increasing temperature and with increasing insulin concentration but which increased by up to a factor of 8 with increasing added arginine. Further, the initial growth rate after the lag phase also slowed by up to a factor of about 20 in the presence of increasing concentrations of arginine. From the temperature dependence of the lag phase duration, we find that the nucleation activation energy doubles from to  kcal/mol in the presence of 500 mM arginine.

Interactive Effects of Temperature, Initial pH, Sodium Chloride, and Sodium Pyrophosphate on the Growth Kinetics of Clostridium perfringens†

1996 ◽  
Vol 59 (9) ◽  
pp. 963-968 ◽  
Author(s):  
VIJAY K. JUNEJA ◽  
BENNE S. MARMER ◽  
JOHN G. PHILLIPS ◽  
SAMUEL A. PALUMBO
Keyword(s):  
Sodium Chloride ◽  
Growth Kinetics ◽  
Generation Time ◽  
Interactive Effects ◽  
Sodium Pyrophosphate ◽  
Lag Phase ◽  
Phase Duration ◽  
Initial Ph ◽  
Effects Of Temperature ◽  
Kinetics Of

The interactive effects of temperature (12 to 42°C), initial pH (5.5 to 7), sodium chloride (0 to 3%) and sodium pyrophosphate concentrations (0 to 0.3%) on the growth in Trypticase-peptone-glucose-yeast extract broth of a three-strain mixture of Clostridium perfringens vegetative cells were determined. The number of viable C. perfringens cells was determined at appropriate intervals by plating on tryptose-sulfite-cycloserine agar. Growth data were analyzed by the Gompertz equation; the gompertz B and M parameters were then used to calculate lag-phase duration, exponential growth rate, generation time, and maximum population-density values. The data indicated that the growth kinetics of C. perfringens were dependent on the interaction of the four variables, particularly in regard to exponential growth rates and lag-phase durations. Cubic models based on the natural logarithm transformation of lag-phase duration and generation time were evaluated and appeared to adequately fit the data. The data suggest that sodium pyrophosphate can have significant bacteriostatic activity against C. perfringens and may provide processed meats with a degree of protection against this microorganism, particularly if employed in conjunction with a combination of acidic pH, high salt concentrations, and adequate refrigeration.

Growth kinetics ofStaphylococcus aureuson Brie and Camembert cheeses

2014 ◽  
Vol 81 (2) ◽  
pp. 252-256 ◽  
Author(s):  
Heeyoung Lee ◽  
Kyungmi Kim ◽  
Soomin Lee ◽  
Minkyung Han ◽  
Yohan Yoon
Keyword(s):  
Growth Kinetics ◽  
Storage Temperature ◽  
Model Performance ◽  
Lag Phase ◽  
Square Root ◽  
Growth Data ◽  
Phase Duration ◽  
Mannitol Salt Agar ◽  
Staph Aureus ◽  
Kinetics Of

In this study, we developed mathematical models to describe the growth kinetics ofStaphylococcus aureuson natural cheeses. A five-strain mixture ofStaph. aureuswas inoculated onto 15 g of Brie and Camembert cheeses at 4 log CFU/g. The samples were then stored at 4, 10, 15, 25, and 30 °C for 2–60 d, with a different storage time being used for each temperature. Total bacterial andStaph. aureuscells were enumerated on tryptic soy agar and mannitol salt agar, respectively. The Baranyi model was fitted to the growth data ofStaph. aureusto calculate kinetic parameters such as the maximum growth rate in log CFU units (rmax; log CFU/g/h) and the lag phase duration (λ; h). The effects of temperature on the square root ofrmaxand on the natural logarithm of λ were modelled in the second stage (secondary model). Independent experimental data (observed data) were compared with prediction and the respective root mean square error compared with theRMSEof the fit on the original data, as a measure of model performance. The total growth of bacteria was observed at 10, 15, 25, and 30 °C on both cheeses. Thermaxvalues increased with storage temperature (P<0·05), but a significant effect of storage temperature on λ values was only observed between 4 and 15 °C (P<0·05). The square root model and linear equation were found to be appropriate for description of the effect of storage temperature on growth kinetics (R2=0·894–0·983). Our results indicate that the models developed in this study should be useful for describing the growth kinetics ofStaph. aureuson Brie and Camembert cheeses.

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