Cytoplasmic membrane fraction that promotes septation in an Escherichia coli lon mutant

Magnetophoretic and spectral characterization of oxyhemoglobin and deoxyhemoglobin: Chemical versus enzymatic processes

A new method for hemoglobin (Hb) deoxygenation, in suspension or within red blood cells (RBCs) is described using the commercial enzyme product, EC-Oxyrase®. The enzymatic deoxygenation method has several advantages over established deoxygenation methodologies, such as avoiding side reactions that produce methemoglobin (metHb), thus eliminating the need for an inert deoxygenation gas and airtight vessel, and facilitates easy re-oxygenation of Hb/RBCs by washing with a buffer that contains dissolved oxygen (DO). The UV-visible spectra of deoxyHb and metHb purified from human RBCs using three different preparation methods (sodium dithionite [to produce deoxyHb], sodium nitrite [to produce metHb], and EC-Oxyrase® [to produce deoxyHb]) show the high purity of deoxyHb prepared using EC-Oxyrase® (with little to no metHb or hemichrome production from side reactions). The oxyHb deoxygenation time course of EC-Oxyrase® follows first order reaction kinetics. The paramagnetic characteristics of intracellular Hb in RBCs were compared using Cell Tracking Velocimetry (CTV) for healthy and sickle cell disease (SCD) donors and oxygen equilibrium curves show that the function of healthy RBCs is unchanged after EC-Oxyrase® treatment. The results confirm that this enzymatic approach to deoxygenation produces pure deoxyHb, can be re-oxygenated easily, prepared aerobically and has similar paramagnetic mobility to existing methods of producing deoxyHb and metHb.

Exploring the role of E.coli derived enzyme, Oxyrase, as an oxygen scavenger to improve the cryotolerance of spermatozoa of Sahiwal bull

The current study intended to optimize the concentration of Oxyrase in the semen dilutor and to evaluate its effect on freezability of spermatozoa of Sahiwal bulls. Supplementation of Oxyrase at 0.125 IU/mL concentration significantly reduced dissolved oxygen (DO) in the dilutor to 4 ppm in 16-18 min at 35 °C. For supplementation studies, a total of 24 ejaculates were categorized into poor and good ejaculates categories (n = 12 each) based on their initial progressive motility. Each ejaculate was further divided into two aliquotes. The first aliquote was diluted with tris-egg yolk extender without Oxyrase (control group) whereas, in the treatment group, Oxyrase was supplemented at the concentration of 0.125 IU/mL of extender. The parameters evaluated include cholesterol and plasma membrane phospholipids (PMP) at fresh, while IPM, acrosomal and plasma membrane integrity, cholesterol, PMP and oxidative stress parameters like lipid peroxidation (LPO), total antioxidant capacity (TAC) and reactive oxygen species (ROS) were evaluated at pre-freeze and post-thaw stages. The IPM and acrosomal intactness were higher (p < 0.05) in treatment group at post-thaw stage in good ejaculates. Oxyrase supplementation resulted in lower (p < 0.05) cholesterol leakage in both categories and lower (p < 0.05) LPO in good ejaculates at post-thaw stage. No statistical difference in ROS was observed between control and treatment groups at all stages whereas, level of TAC was higher (p < 0.05) in the treatment group compared to control group at post-thaw stage of both categories. Therefore, Oxyrase as an oxygen scavenging agent could preserve the post-thaw quality of Sahiwal bull spermatozoa.

Effect of combination of Oxyrase and sodium thioglycolate on growth of Clostridium perfringens from spores under aerobic incubation

Clostridium perfringens is a strictly anaerobic pathogen that requires absence of oxygen for its growth in laboratory experiments, which is usually attained by using an anaerobic chamber or anaerobic jars. However, it has been demonstrated that C. perfringens may survive for short periods of times due to its adaptive response to O₂. Therefore, the objective of this study was to explore the application of Oxyrase (OX) and sodium thioglycolate (ST) as oxygen scavengers, used alone or in combination, for observation of the growth of C. perfringens under aerobic incubation. The growth of C. perfringens from spores in Schaedler Anaerobe Agar containing different levels and combinations of OX and ST was observed at temperatures between 20 and 50 °C. The kinetic parameters, including lag time, specific growth rate, and maximum cell concentrations in the stationary phase, were determined. The results indicated that ST at concentrations of 0.025 and 0.05% (w/w), although allowing eventual growth of C. perfringens, prolonged its lag times, while OX at 1.5% only allowed growth at a lower growth rate in comparison to anaerobic incubation. OX at 3% enhanced the growth of C. perfringens at temperatures between 30 and 50 °C, while higher levels of OX were needed in the medium to support the growth of C. perfringens during storage at 25 °C (>6% OX) and 20 °C (>9% OX), due to the effect of temperature on enzyme activity. No significant difference was found in the kinetic parameters of C. perfringens incubated aerobically with OX and the control (without OX or ST) in an anaerobic chamber. Therefore, OX at appropriate concentrations may allow the observation of the growth of C. perfringens under aerobic incubation conditions without the need of an anaerobic device.

Review of current methodologies to isolate and identify Campylobacter spp. from foods

This article summarizes the most effective protocols to isolate Campylobacter spp. (mainly Campylobacter jejuni and Campylobacter coli) from food, primarily poultry products, and includes a summary of the current methods recommended by the Food and Drug Administration and the U.S. Department of Agriculture in the USA, and ISO in Europe. The recommended temperature for incubation of the samples throughout the isolation procedure is 42°C. The enrichment of the samples for 48h, which can be performed under aerobic conditions, is recommended to achieve a detectable number of Campylobacter cells. Bolton broth or buffered peptone water supplemented with cefoperazone and amphotericin B is commonly used enrichment broths. The transfer of the enriched samples to plate media using membrane filters helps to obtain pure Campylobacter colonies. Charcoal cefoperazone deoxycholate (CCDA) is the best choice among all plate media. There is no need to add oxygen quenching substances or blood to enrichment broth for the isolation of Campylobacter spp. However, the addition of blood to plate media aids in differential identification of presumptive colonies. Phase contrast microscopy and latex agglutination tests are confirmatory tests for presumptive Campylobacter isolates. The use of multiplex polymerase chain reaction (mPCR) assays is the simplest and most rapid method to identify isolates to the species level. mPCR assays, or other methods assessing DNA sequence variations, will probably become the confirmation procedure of choice in the future. Recent work with retail broiler meat has revealed that the rinsing of meat is more sensitive for the recovery of naturally contaminated retail broiler meat than current reference methods and requires less time for preparation and processing of the samples. This protocol could be coupled with DNA-based methods for a fast screening of positive samples.

Pasteur, oxygen and the anaerobes revisited

As a biochemist, Louis Pasteur focused on fermentation, demonstrating that it was a vital process. In 1860, he discovered anaerobic life and the strict anaerobes, particularly those responsible for butyric fermentation. Then, in spite of his lack of medical background, Pasteur turned to investigating the role of bacteria in human and animal diseases. In 1877, Pasteur and Joubert described for the first time a pathogenic anaerobe, the 'septic vibrio' (now Clostridium septicum). Not only was the bacterium cultivated, but the disease symptoms described and the disease experimentally reproduced. Pasteur also described what are now known as mixed anaerobic infections. A historical review of Pasteur's work is made in the light of our present knowledge of this field.

Stressed salmonella are exposed to reactive oxygen species from two independent sources during recovery in conventional culture media

Previously, Stephens et al. [J. Appl. Microbiol. 83 (1997) 445-455] developed a sensitive technique for studying the resuscitation of low levels of stressed Salmonella. Using this technique the influence on recovery performance of the peptone component of buffered peptone water was investigated. Within 12 different peptone types as much as 3.5 log10 cells/ml difference was observed between the best and worst performing formulations. Poor recovery performance was linked to reactive oxygen species (ROS) generation through auto-oxidation of reducing sugars and photo-sensitisation of sensitive components such as riboflavin. Supplementary recovery agents were explored with only Oxyrase, which has both enzymes to degrade ROS and the ability to rapidly turn a medium anaerobic, having any significant effect. It improved the speed of recovery and increased, by up to 100-fold, the number of stressed cells recovered. Stressed cells were further studied by flow cytometry with cell sorting, based on the staining pattern from a novel fluorochrome combination, into good and poor recovery media. It was identified that within a stressed population the removal of all oxygen protected actively respiring cells the most by forcing them to generate energy from anaerobic metabolism thus avoiding any risk from accidental endogenous ROS generation. The recognition of two independent sources of oxidative stress in the routine use of conventional culture media is discussed in relation to pathogen detection and other areas of food microbiology.

Neighbour restoration: a possible explanation for some "broken" survival curves of UV-irradiated Escherichia coli K12 cells

Survival curves for UV irradiation of five non-filamenting strains of E. coli K12 decrease exponentially at moderate levels of radiation but are broken at high levels of radiation. That is, it appears a change in the slope of survival curves, featuring a tail. As this phenomenon was observed with strains bearing uvrA and recA mutations it must be independent of the products of these genes. Experiments with isolated surviving colonies and synchronized cultures eliminated genetic and phenotypic heterogeneity as reasons for the tails in the survival curves. UV survival increased 10- to 15-fold when UV-irradiated cells were plated either with cells unable to grow in the plating medium or with bacterial cell-free extracts. We suggest that factors related to the high cell densities used to obtain survival curves at high radiation levels (neighbour restoration) could be responsible for the survival increases, generating the tailed survival curves.

The use of microbial membranes to achieve anaerobiosis

The cytoplasmic membranes of many aerobic and facultative bacteria contain enzymes that catalyze the reduction of dissolved oxygen to water. Preparations of small particles derived from such membranes can be filter sterilized without loss of the oxygen-reducing enzymes. These particle preparations can be used to produce anaerobic conditions in a variety of biological environments. They have been shown to stimulate the growth of many anaerobic bacteria and can also be used to stabilize oxygen-sensitive chemical reagents. The particle preparations are stable for long periods of time. They are functional over a pH range and temperature range frequently encountered in biological systems. Various techniques for using the particles are presented. The advantages and limitations of this new approach to achieving oxygen-free conditions are discussed.

Characterization of an iron sensitive Mud1 mutant in E. coli lacking the ribonucleotide reductase subunit B2

The mutant, generated by a Mud1 insertion, formed long non-viable filaments in the presence of iron and air. Under anaerobic conditions normal growth in the presence of iron was observed. The mutation was mapped by P1 transductions at 48 min on the genetic map of Escherichia coli. By Southern blotting the insertion point was determined to be in nrdB, the structural gene for the ribonucleotide reductase subunit B2. The mutation could be complemented by the cloned nrdB gene. Up to now it was assumed that E. coli possesses only one enzyme for the synthesis of deoxyribonucleotides and only conditional lethal (temperature sensitive) mutants were isolated in nrdB. The insertion of Mud1 in nrdB should lead to a complete loss of the essential B2 subunit. Since the strain was able to grow under anaerobic conditions on minimal medium lacking deoxyribonucleotides and additional pathway for the synthesis of deoxyribonucleotides is postulated.

Mutations in Escherichia coli that effect sensitivity to oxygen

Fifteen oxygen-sensitive (Oxys) mutants of Escherichia coli were isolated after exposure to UV light. The mutants did not form macroscopic colonies when plated aerobically. They did form macroscopic colonies anaerobically. Oxygen, introduced during log phase, inhibited the growth of liquid cultures. The degree of inhibition was used to separate the mutants into three classes. Class I mutants did not grow after exposure to oxygen. Class II mutants were able to grow, but at a reduced rate and to a reduced final titer, when compared with the wild-type parent. Class III mutants formed filaments in response to oxygen. Genetic experiments indicated that the mutations map to six different chromosomal regions. The results of enzymatic assays indicated that 7 of the 10 class I mutants have low levels of catalase, peroxidase, superoxide dismutase, and respiratory enzymes when compared with the wild-type parent. Mutations in five of the seven class I mutants which have the low enzyme activities mapped within the region 8 to 13.5 min. P1 transduction data indicated that mutations in three of these five mutants, Oxys-6, Oxys-14, and Oxys-17, mapped to 8.4 min. The correlation of low enzyme levels and mapping data suggests that a single gene may regulate several enzymes in response to oxygen. The remaining three class I mutants had wild-type levels of catalase, peroxidase, and superoxide dismutase, but decreased respiratory activity. The class II and III mutants had enzyme activities similar to those of the wild-type parent. Our results demonstrate that mutations in at least six genes can be expressed as oxygen sensitivity. Some of these genes may be involved in respiration or cell division or may regulate the expression of several enzymes.

Restoration of viability to an Escherichia coli mutant deficient in the 5'----3' exonuclease of DNA polymerase I

An Escherichia coli polA (Ex) mutant that is usually inviable at restrictive temperatures (43 degrees C) was found to grow normally at 43 degrees C when incubated in the presence of a membrane-containing fraction prepared from E. coli. This membrane fraction causes anaerobic conditions that are necessary but not sufficient for restoration of viability since some component present in the membrane fraction is also required for colony formation at 43 degrees C. The accumulation of small DNA fragments typical of aerobic growth of the polA(Ex) mutant was also seen under anaerobic conditions. The polA(Ex) strain was also much more sensitive than the isogenic wild-type strain to hydrogen peroxide.

Anaerobic incubation enhances the colony formation of a polA recB strain of Escherichia coli K-12

Escherichia coli strain E247 (polA1 recB21) has reduced colony formation (even at the permissive temperature of 30 degrees C) because of a poor suppressor mutation (sup-126). The colony formation was enhanced in the absence of oxygen about 3-fold at 30 degrees C and 10(6)-fold at 43 degrees C, suggesting that a polA recB strain was inviable due to oxygen toxicity. Colony formation was also increased by incubation in an agar medium containing the reducing agent thioglycolate and incubation in the presence of chloroform-killed Saccharomyces cerevisiae pet+ cells, but not pet cells. Since the E247 strain viability was inversely dependent on the oxygen pressure and since the strain was more sensitive to superoxide radical than either the polA or the recB mutant, it seems likely that the polA and recB genes play a role in repairing DNA damage during respiration.